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Foreword

III placing Valve Timin g for Maximum Output in the hands of Top TlIllers, Ed lskenderiall is passing on a digest of hi s 25 \ cars hard WOll experiellc.c in the Hop Up and En gine Mod ifications hcld.

l\lany of the tips in this hook arc not generall y knowll and oth e r ~ ;ne oft ell m'Cl'looked or not corrcctly Ilmlcrstood . \ Vhcn properly applied th ese tips will sa ve many hours of w~l s t ed \\'ork and money.

Years ago Ed bccalllc convinced that the cam shaft \-v,.I s the backbonc of tllc racing cng in e and t-lwt: greater power wOllld conic fro lll better ca mshaft design and rcfinement. v\:' ith this Olle though t ill mind he clccidcd to concentrate his kn owledge in the manufact l1l'e of fin er CllllShafts, cach ans\\'ering the spcc ihc Il eells of th e en and type of raee entered. For 15 years speciali7a tion in the design :1ll c1 refinernent of the world 's fincst racing cams has been his onc tllollght.

Toda y, the Iskenderian organi7a tion pmsesses the wo rld 's largest fac ilitics for the designing, tcsting and prodllctioll of racing Glln s ,1Iltl valve gear componcnts. A new modern building providing a 400 0 incrcase in working space will help continue this leadership in the ca mshaft field.

Ed works closely with America's Top TUllers-Racing Drivers alld Mecha llics. From assoc iated tests and th e interchange of expcriences v,:ith tllesc mcn eOIlle the practical d

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Pa ge THE FIELD OF CAM DESIGN

WORKING UP TO THE POLYDYNL .. ... .. ...... ... .. _........ ..... ...... .. . 38

TOP TUNERS TIPS

HOW TO DETERMINE TOP DEAD CENTER ACC UR ATELY .. ... . _ .... ... 45

Posi.tive Stop Method

PROCEDURE FOR CHECKING VALVE OVERLAP

WITHOUT DIAL INDICATOR OR DEGREE PLATE ....... ... .. ......... ... 4 7

POSITIVE METHOD FOR FINDING TOP DEAD CENTER ... ..... .. .. _..... 48

KNOW YOUR SPARK LEAD .... .. .... . 49

CHECKING A CAM IN THE ENGINE. 50 Eliminat ing Slac k in Camshaft Drive, Check Opening and Closi ng of Valves, Drawing the Va lve Lift Curve and Graph , Valve Lash and Val've Timing, Maximum Performance Requires a High Speed Camshaft, Select the Correct Rear End Ratio

JUGGLING TAPPET CLEARANCE ......... ..... .... .. .. .. .. .. 53 Effect s of Altering Valve Lash, Increasing Tappet Clearance Short ens The Timing Working Procedure

FEATURE ARTICLES

VALVE TIMING FOR TOP PERFORM A NCE by Don Francisco... .. . SS

CORRECT SPARK LEAD by Ted Frye ..... 63

EN GINEERED SPRING ASSEMBLIES ... 71 Chrys ler, Mopar, Chevrolet, V8, Ford V8, Oldsmobile V8

NEW PRODUCT DEVELOPMENT.. .... 76 Chevrolet Forged Aluminum Offset Connecting Rod, Chevrolet Dual Spring (New Intereference Design) , Ford Special Alloy Va lve Springs , New Anti Pump Up Hyd rauli c Racing Tappets , High Quality Oversize Exhaust Valve (for Chevrolet V8) , Screwin Rocker Arm Studs (Exclusive Jam Nut Des ign), Li ghtweight Aluminum Spring Retainers, Heavy Duty Split Valve Locks

Valve Timing for Maximum Output

THE STOCK CAR CAMSHAFT

The camshaft dcsign of th e American Passenger Car Engine stresses low speed performance and smooth idling. To bring out thesc char acteri stics I:; to 20 '!o of the horsepower is sacrificed. This Oll tpll t can be increased from 20 to as high as 100 % with the usc of our reground racing camshafts tcamed with higher compressIon ratios and multi ea rburetion.

TOP CENTER TOP CENTER

INTAKE CLO SE S EXHAU ST OPEN S BOTT OM CENTER

BOTTOM CENTER

BASIC CAM DESIGN

The ideal calli w01lkl open the intake valve instantly to full lift at approxilllately top dead center, dwell in the full open position until approximately 40 degrees after bottom center and then close instantly. Naturally, such abrupt ac tion wou ld crea te terrific mechanical stress and many other complica tion s. Consequen tl y cams must be contoured to open and close the valves in a more gentle manner.

OVERlAP

It is now und erstood that in actuating the valves we are- limited to certain rates of valve acccleration and deceleration. Since it is neceSS

INTAKE OPENS In the timing diagram one notes that the intake va lve begins opening 20 degrees before top dead center or hefore the piston starts on the suction strokc. This is done to givc the \"alve a head start on the piston a11d we find that at top center the valve will he wcll off its seat, so as to offer little resistance to th e incoming cknge. INTAKE CLOSES Now 110te that thc intake va lve remains opened some 64 degrees aftcr bottom cellter which is long after the piston has changed direction and is coming up on the compress ion stroke. This is bes t explained by the fact that the intake chargc having been in motion builds up killetie e11 ergy and tends to c011tinue to fl ow long after th c piston changes direction, should the intake valve have hecn closed at bottom center here would be a considerable throttling effect on the intake charge. EXHAUST OPENS Looking at the exhaust va lve, it is seell that th e valve begins opening some 64 degrees before bottom centcr or beforc th e power stroke has actually becn completed , This slight loss of useful power is offset by

t~e fact that the hot exhaust gasses leave th e cylinder partially und er their own pressure, thereby rcducing the cffort on the enginc's part to cxpel th e burnt gasses on the upward stroke of the piston, eXH AUST CLOSES Notiec that thc exhallSt va lve remains open for some time after top ccntcr, here again kinetic energy comes into play in that th c hurnt gases continue to fl ow out and seave11ge thc eylillder. It might he added that on some inclined overh cad valve cngilles when definitc diameter and length of exhaust stacks arc uscd a mild super charge is effected by the exhaust gasses. Actually drawing th e intake charge in during the shor t overlap period , THE VALVE OPENING DIAGRAM From the forcgoing it is obvious that it is of no LIse to compare the cam dcs igns with respect only to actual points of valve opening and closing, The important fa ctors are lift and rate of lift and only when a graph is drawn by plotting valve lift with respect to crankshaft rotation can a good study be made. The necessary tools arc a .)00" minimum range dial test indica tor to read valve lift in thousandths of an inch and a timing disk to be attached to the crankshaft. Valve Lift is then checked every 5 degrees of crank rotation and recorded on graph paper giving the valve opening diagram .

Page 4

The Camshaft

TYPES OF CAMS There arc 111 a11\' types of cams, such as face cams, cylinder cams, the familiar autoIll otive tvpe of C IIl1 and manv others which we will not go II1to nov,. It is sa fe to say that during thc development period of th e

Although most top tuners and racing enthusiasts now turn to the more efficient overhead valve engines it cannot be denied that flatheads still account for amazing performances.

The Hathcacl engine may be obsolete and suffering trom porting and combustion-chamber deficiencies, but it has one tremendous advantage over a push-rod overhead valve system, and that is an extremely cOll1pact and sturdy valvc gear. In fact it is similar to an overhead camshaft design but tllrned upside down. There are no flexing pllsh-rods, rockers and roekershafts. Via the cam follower the movement of the cam is transferred directly and in the same measure to the valvc. Another advantage of the flatheau valve design as compared to the push rod OHV motor is that the strain and consequently the wear on the camshaft is very mlleh less, due to the fact that the valve springs exert their tension directly on to the cam instead of working through a rockcr arm ratio (1.4 to 1.8 ) on the OHV cngines. Last, but not least, inaccmacies or wear in cam contour have less effect than with OHV engines where inaccuracies are magnified on account of the rocker ann ratio just rderred to. CAM CONTOURS AND VALVE TIMING Although autol1loti\e ealllS arc made III lllan\" differcllt shapes , they are all derivatives of the silllple cam ShOWll ill thc accompanYll1g illustratioll. Basicallv all callis lIsed in thc car cnglllc for operating the valves cOllSist of a base circle, two fI ;lllk circles

Types of C am Followers -~---------------------------~--

CAM FOLLOWERS (ALSO CALLED LIFTERS OR TAPPETS) The timing characteristics of anv particular cam cannot be asscsscd just by studying the cam contour itself. To accurately dctermine the exact naturc of the valve action resulting from the use of any particular cam we'll have to know what kind of lifter is used with the ca m. 'f he accompan ying illustra tions show two cams wI! icll differ wielclv in contour; one is a convex,Ranked cam with a small nose circle opera'ting with a Rat mushroom follower, alld the othcr is a concavcRanked cam with a large radius nose circle \\.hich is used in com-

ROLLeR FOLLOINE~

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.SKENDERIAN

rul1l1aru ~~ and ENGINEERED KITS

The Hardface Overlay Cam is intended only for competition use and is not recommended for slow speed driving. Now, it is possible to install a hi gh speed competition cam with the famous Isky flat tappet Polydyne Profile performan ce ......... and still be used equally well for either slow speed road use of drag racing. This has proven to be the long awaited answer for those who felt the economic pressure of owning two cars and the inconvenience of hauling their competitive cars to and from the strips. Roller Cam and Tappet Assembly, developed in the Research lab at Iskenderian's took many long months of testing and developing before all the obstacles were successfully solved and perfected. They have proven to be a tremendous boon to racing. Installation of these Roller Tappets is quick and simple since they can be dropped into place in only second s. Special patented self-locking keys eliminate the need of broaching tools, welding, drilling, tapping, etc. These are high quality roller tappets with 100% bearing area .

ISKY PATENTED AUTOMATIC SelF-LOCKIN G NON-ROTATING ROLLER TAPPETS

Iskenderian roller tappet bodies are lengthened to bring them above their bosses. This permits a successful bridging, or keying of each pair of intake and exhau st tappets. This patented design allows full freedom for reciprocation whil e at the same restricting rotation. This design also provides a secondary advantage of using a shorter and more rigid pushrod. Isky Ro ll ers are made to unusually close tolerances ar.d incorporate the traditional fine Isky workmanship.

ISKY ROllER TAPPET FEATURES

CARBONITRIDEO ALLOY STEEL BODY. For desirable 6062 Rockwell hardness, combined with a tough inner core. Highly polished surface for minimum frictional losses.

Exclusive full length, full bearing struts support roller body against thrust loads.

Precision roller bearing has greater wall thickness, rides on precision needle bearings. All parts of the highest quality 5200 chrome ball race steel.

PRECISION 'TRU'ARC' SNAP RINGS - Retains beefy sha ft. Obsoletes inferior peening and ' riveting methods. Bearing assembly can be replaced in the field.

EXCLUSIVE BIG .350 JOU RNAL. - Rides direclly on needle bearings, eliminating former vulnerable thinwall inner races. Has over 5 times the sheer strength of any

thing else on the market.r THE ISKENDERIAN ULTRA REV KIT With the installation of the Ultra-Rev Ki t it is now poss ible to obtain power gains and effi ciency never before ob tained. Engine range is extended beyond 10,000 rpm without valve float.

Page 10

the fac t that this cam gi\'cs cx trcIlI cl ) rapid opcning ,11)(1 clos ing of tlie \'a lves combined with ,111 extra high 1',lIve lift, Icwlll1gs ,mel we,ll" rcmain within pcnlllssible lilllits.

Th e 404 cam and lifter combina tion h as a n im pressive competition record and it is mainly respoll sihlc for thc b et tha t so lll;lll\ ' Aatheacls still give sll ch an exccllent aecollnt of thcmselvcs both III d r,lg and spccc1 evcnt s.

Racing Valve Springs

\\ Compound racing' " alve sp rings, H ,D . !rla iners, u/ashN s,

li f /('(' /Jll llollS and ho/,'saws f iJ r in s/a! ling same .

VALVE SPRINGS O nc of th c lll () \1 \ it;ll part s ill th c \', llIc i.;l'; l1 of ;1 modUli Iligh spccd CllgIII C is th c I ,!l le spn ll g, \\ 'l' lllli sr he ll III 111 11 ICI th ,lt the C3m, opcr;llL'cl 1;II1'c lll otioll is ,I spcc l;il Olle of \\ 'Ilich ollh th c OpClll11 g p iJel sC IS J positil 'c mOl CIllC ll t , rc lllli g 0 11 th e tClI S]OI I of its vall e ,) prill i~ for t he clo

VALVE FLOAT It1(1 ,IS these cOllclitions arc in til e c lse uf ,I stock enginc, th el can be liIs,lstWIIS Il'ith ,I high spccd eO Jl1petition cnglll c, At I'cn Iligh COIllpression IAios (12: 1 ,lIld higll cr) th c clear,lII ec volullIc (combustion Sp,ICC ) ,Illme the pi s tOil lenels to bee(HJlc I cn sndl, le,ll'illg little leell,1\ for 1,lke IIl00 elll ellts, cspeC' i

is bv ll ~i n g two vah 'e spr ings for eac h \"al\"e, an inu er and ,111 outer spring. These spri ngs each have differell t natural freyneneies, and although they do suffer from surge iuc1 iv iclual1 y (a ll sp ri ngs do) it doesn' t happen Si11l111taneo llsk T h is is clead) shown in the Iskie illustration . An additional a dvantage of uling dual springs is that it provides a safety fa ctor in th e event of spring breakage which otherwise cou ld cause seve re engine d a mage. Some manufacturers

not run before. The most important thing to watch for is to make sure that the spring (s) do not stack solid (i.e. wi th the individual co ils actually touching each other, sometimcs called coil-bound ) when the va lve is full y open ( t8ppet rid ing on nose of the cam ) .

MEASURING VALVE LlFl The v;) lve lift is eas ily ealcubted. On flathead engines or overhead eamsh c()l1lpctitioll rU l1 s. A comparison of spring tension will give us an indication of the amount of "load-set" that has occurred . lh IO;lci -sct \\C IIlCII1 thc slight eleerclsein tension (:It'l t;i\c ll Sp lillg 1c1l,c;th) til ,l! OCClIIS ill evclI spring ;Ifter it has been In operati()11 f(lI ,I (C It;lil1 IIUl1lhcr of hours. Our r;lCing spri ngs however kl\l' hccil trcll"ccl ill ~lIch ,I \\ ';1\ ' so ,IS to keep tlli s lo;]el-sett ing to a ll ahsolu te l1linilllUI1J. Om ~1)J"il1gs ,Ill' ,lccur;ltcly ,11Ot-bbstcel and pre-set ;lIIel prm'ic1 il1g th:li' tilc\ ' ,IrC 1I0t oper;lt l11g under too llnfa\'or

til

ADJUSTABLE CHROME MOLY TUBULAR PUSH ROD

q):{]liH ~1 Male End I Male End

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NON-ADJUSTABLE CHROME MOLY TUBULAR PUSH ROD

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NON-ADJUSTABlE CHROME MOLY TUBULAR PUSH ROD

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The proper method of measuring push rod length in the autoISKENDERIAN industry is to inc lude a theoretical overa ll length. Thi s, however, is difficult for the average individual s'ince special fixtures areMETHOD required. In the interests of accuracy, and avo idance of con fusion we have adapted the above method of measurement. This eliminates the difficulties that arise when making measureOF MEASURING ments in the field or when installing specia l length push rods specifically ordered by our customers. The above illustrations PUSH RODS should be self-explanatory.

CHECKING FOR I 'F ~.J to 1/ 8" Q(L:>i ~ () Allow 1/ 16" INTERFERENCESafe ty Margin

BETWEEN

SPRING RETAINER

AND

I VALVE GUIDE n 8e sure to check the clearance between the valve guide ends and the spring retainer with valve in open position (see illustration ). WARNING : Some engine builders, when porting cylinder heads, will knock the replaceable guides slightly up from their stock position, so as to have free access with the grind stone . Naturally th is will cause them to interfere with bottom of the spring retainer when the valve is fully opened. Also when installing a high lift cam this may cause retainer to interfere with guide, as most cylinder heads only allow sufficient clearance tor stock low lift cam. To correct this poss ible interference, va lve guide must be machined down to allow at least i / 16" to 1/ 8" safety margin at full valve lift.

Page 18

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CORRECT METHOD FOR ACCURATELY MEASURING VALVE SPRING LENGTH

Check for 'fitted dimension '. This means when valve is seated. For satisfactory performance it is mo~t important that they be installed precise ly. This is especially important in over head valve engines. Illustrated is one of our spr ing combinat ions, consisting of an Outer Spring, and an Inner Spring, and a step Spring Retainer. An accurate spr ing testing fi xture is necessary for these tests. If none is available have the springs tested at a local garage or parts house. To confirm the spring tension of the Outer Valve Spr ing, with the valve sea ted (c losed), measure the overa ll length of the spring when it is installed from the spring base 'A' to where it contacts the spring retainer '8'. Remember measu re the spring porper only, and do not include the thickness of the retainer or sp ring shims.

To check the tension of the Inner Spr ing with valve seated you will have to take into account that ,it sits on the step portion of the retainer, and you will have to allow for this. Most Iskenderi an cams produce a li f t of .440" to .520" at the valve. The most important thing to watch for is that the springs do not stack solid or coi l-bind when the valve is fully open . Know your total valve lift ... Then sta rting at the fitted dimension, with both the Inner and Outer Spring and Retainer assembled in a checking Spring Tester, simulate the va lve opening and compress assembly to full lift. Make sure springs have at least a .060" safety travel margin beyond the full valve lift , .440" or .520" plus .060".

Page 19

Chrysler hemispherical eylinderh ead s. Our special Chrysle r valve spring kit has heen instrumental in ob taining an extra 1000 rpm , and Chrysler engines thus converted run satisfactoril y at over 7500 rpm. Wc can supply the special hole saws necessary for installing these va lve springs (e ither on 8 loa ll basis or solcl outrigh t ).

ADJUSTING SPRING TENSION WITH WASHER S I n some in stances th c spring tension e8n be conveniently in creased by plaClllg washers Oil the spring base. This is especiall y important in those cases where the valves have bcen sunk into th e eylinderhead to prevcnt in terference between the v8 lve head ;md pis ton crown (especiall y 0 11 Chcvrolet \,R and Buick V8). \\'e can suppl y a vJrietl of these shim washers for pr,letieally cvery

engi nc. But here again II 'C ~Icl v i se to proceed with ca ution. Too much shimming should be avoided at all cost . Cheek th e spring tcnsion aecorclin g to th e methods di ,ell ssecl ,lJlel avo icl conditi ons of th e spr ing coils st;]cking solid (co il lli nel ) .

Cylinderhead Design

THE CYLINDER HEAD It has been sa id th8t the cylillC1crhcad is the 111 0s t illl jlortzlllt p8rt of a competition engin e. While this is a very hrwel ota tclll cnt, it cl oes eontlin a geml of truth . O nly by using an effi eicnt el linclcrllead wi th effieicnt porting C

\Vh cn we go back through fi le '..cars ,1l1tl stud y the clesign features of th c most s ll cce, ~,flll rac ing (';lrs \\ 'c' ll di scO\'er that the majority of these \\ere pO\\crcd 1\ itl! engines des igned ;)long simibr lill es.

III th c stock (',l[ fielcl ()\'erhead c

V\'e must keep in mind hov\ever that the forcgoing onl~' applies to passengcr car engines. Thcre can be no doubt whatcver that a cylinderhcad with h cm isphcrical combustion-chamber is the ultimate for racing purposcs.

WEDGE SHAPE COMBUSTION CHAMBER The wedge shape combustion chamber is typical of contemporary U.S. design. The combustion chamber shown in the accompanying illustration is completely machined for accurate control of the com-

Completely machined wedge-shape combustion chamber which is typical of contemporary u.s. design practice.

pression ratios in the various cylinders, an additional advantage being tha t ca rbon deposits are less likelv to accumulate than on rO\1gh cast surfaces . Also typical of these combustion chambers is the narrow "quench" area which covers part of the piston head area, the main ohjecti ve being to promote turbulencc and to shorten the effective Aamc travel. Note th at thc grca tcr part of thc combustible mixture is concen trated close to thc spark plug. TIns part of the combllstion chamber has a small ratio of sur facc to voll1llle and this restriction to rapid heat dissipation makes it the hottcst arca of thc combus tion chamber. This insures quick initial burning as soon as the plug fires, but detonation is prevented by the spreading of the combustion flame into the flat quench area which is a relatively cool part of the combustion-chamber on account of its high surface to volume ratio. \Vhether or not the happenings in this typc cylinderhead go

accorcling to theo ry, the fact remains that engines wi th correctl y dcsigned wedge shape combustion chambers are noted for smooth

Page 24

rullnillg and remarkable fuel economy. And although their efficiellcy at ultra high speeds does not quite approach that of their comins equipped with hemispherical cylindcrheads, it cannot be dcnied that members of the form er type have acquitted thcmselves very wel l in competition, especially in drags. The reasOli that engines with wedge shape combustion chambers are so popular in racing is thdt they are in many ways more practical than their more complicated counterparts with in cli ned va lves which only show a power-surplus of some significance near the top of the power curve.

IMPROVING ENGINE BREATHING Of vital importance to the performance of any competi tion engine is its ability to "brea the:' By this we mean the ability of the engine to fill its cylinders with fresh combustible mixture and the effective exhaustion of the burned gases. An often used and more scientific term is "volumetric efficiency:' W e all know that fresh mixture is admitted into the cylinder when th e mtake valve is open and the piston on its way down thus creating a depression in the cylind er. Although we are used to saying that the mixture is "sucked " into the cylinder it is more accurate to say that the gas is " pushed" into the cylinder by the atmospheric pressure. The volumetric effi ciency of an engin e depends on the effec tiveness of its breathing apparatus, i.e., layout of intake manifolding and passages, the carburetor set-up and last but not least the camshaft and valve gear in general.

Better Volumetric Efficiency

VOLUMETRIC EFFICIENCY It should bc clear that if the intake passages are long, narrow and tOltUOllS it would he impossible to achieve effective fillin g of thc cylind er, espcciall v at high specds when the intake va lve is open for only a split second. Should we succeed to fill the cylinder :):j full at a given engine speed we say that the volumetric efficiency of tha t engine at that speed is 75%. This 75'/( denotes the rat io of the volume of the gas drawn into the cylinder (corrected to atmospheric pressure) to the swept volume of the piston (i.e. piston displacement ). No engine with normal aspiration attains a volumetric effi ciency of a full 100% at an y engin e speed, (although cylinder fillin g generally is fairly complete when the engine is pulling at low speeds with widc open throttle), but some engi nes are better in this respect than others.

Page 25

A valuable index as to whether th e performance of an engine is in keeping with the potentialities offered

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joh. In fact, large passages and small valves are a bad combination which my render the engine inflexible at low speeds . Convcrsch ', the combination of very large valves and an unmatched (too ~arrow) porting layout is equally as bad , IVhich coul ci resu lt ill pcrform;mcc in ferior to wh;) t wou ld h;)vc becn obtained with the stock sctup.

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THE ISKENDERIAN CROSS-flOW CAMSHAFT Our new "Cross-Flow" camshafts have been especially designed for engines with hemispherical combustion chambers (Chrysler products and Ardun-Ford cylinderheads). We already stressed the fact that this type cylinderhead is very efficient, allowing the use of very high compression ratios without res tricting the gasflow around the valves. Our Cross-Flow grinds have a special contour which utilizes to the full es t extent the excellent flow characteristics inherent in the lateral valve set-up, in other words permitting the flow area of both valves to be as effective as is practically poss ible. Volumetric efficiency is particularly high in the top rpm range

due to the special scavenging action given by these cams at the valve overlap period (when the valves are open simu ltaneously!.

BLOWERS and FORCED INDUCTION DRIVES EDITOR'S NOTE: A complete discussion on all the ramifications of blower installation would consume many pages. Since technical details would concern only a comparative few of the allout competition minded enthusiasts we will confine our information only to the barest highlights. For those who desire it complete informative literature is available by writing direct 10 the Iskenderian factory.

SUPERCHARGERS: - A Supercharger, to describe its most basic function, is a mec~anical 'iron lung' that compresses the air-fuel mixture from the carburetor, compresses it, and forces it into the intake manifold. Under such pressure it is forced into the cylinder with each opening of the valve. Although there are several types available, by far the most popular to dragsters is the Roots type. This is due mainly to availability and economy. GMC manufacturers this type (6.71) for large deisel engines. They have proven ideal for dragster installation.

BLOWER DRIVES:-The success of a supercharger installation, of course, depends on the assembly that drives it. Like most new equipment innovations there have been a lot of hastily contrived assemblies made available that are lacking in anything close to maximum efficiency, durability and rigidity. Extreme care should be exercised before selecting any assembly that the unit in mind has a proven history of satisfactory service and long life.

Right: An Isky Forced Induction Drive Assembly for the Chevy 283 type engine.

Water

Page 30

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Pump PLlU e.. ~Jl:;~~::1~

The Poppet Valve

VALVE OPERATING CONDITIONS The poppet valve is one of the key links in the breathing system of our engine and it must be treated correctly in order to get top perfonnance . Through the years an enormous amount of research has gone into valve design and valve materials with the result that the modern valve has become extremely tough . And this is just as well because the valves operate under very unfavorable conditions. The exhaust valve especially leads a very rugged life. Operating under extreme heat conditions it usuall y is cherry red and it is truly amazing that it stands up to the punishment for so long without breaking down.

VALVE MATERIALS Exhallst valves arc usually made out of special high alloy and austcnitic stcels which retain thc ir strength at high tempcraturcs much bcttcr than normal ca rbon steel s. Extreme heat reduces the tensile strength which may lead to valve stretch and valve breakage, especially in our reworked engine where seating loads will be higher. It is safe to say that the majority of valve failures are caused by insufficient cooling of the valve. Cooling of thc valvc always has been a dIfficult problem cspcciall y of the cxhaust va lve. The intake valve at least rcccivcs

A well designed racing cam will have sufficiently long clearance ramps to allow valve settings adequa te to prevent the exhaust valves from losing all their clearance. On engines using superchargers or nitrated fuels this situation is much worse. If you regularly have trouble burning exhaust valves it would be

worth while to experiment with wider than nonna l valve clearances.

AUSTENITIC STEELS

Alloy steels with a chrome, nickel and manganese content of more than 30% are usually referred to as austenitic steels. These alloys offer a high res istence t.() ox idation at high temperatures and th eir tensile strength also remain s high at these temperatures. Disadvantages of these alloys are the non-hardenability and the lower heat conductivity. The hottest area of the exhaust va lve is the fill et or radius where

the stem curves into the valve head . With stock engines this area not infrequcn tl y attains a tempera ture of 1200 degrees F, but these tempcratures are far exceeded in hot competition engines. The valve head and valve stem run cooler due to the heat transfer to valve seat and guide. To promote th is heat transfer it is important to keep the areas around the va lve sea t and the va lve guide as cool as poss ible. Some Illanufac turcrs fit their cool ing sys tems with water di st ributing tubes or nozzles to di rec t a stream of cooling wa ter to the critica l hea t areas. Thcse dcvices should not be tampered with and if they have been rCllloved for somc reason , makc sure that they arc re- installed correctl y.

We already mentioned the bct that the intake valves run much cooler ;md the normal hardenable carbon stecls arc sa tisfacto ril y used for th c iMake val ves.

VALVE SEATING FOR RACING

To prevent overheating of the valve, proper seating and the correct guide fit is important. T hc va lvc seat must be wid e cnough to providc sufficient arca for hca t Aow, yet it should not be so wiele as to o ffer excess ive res istall ce to the incoming gascs . Therc arc no hard and fast rul es for racing but the sea t wid th is usuall y held between .060 and .075 in. for the intakcs and .080-. 100 in . for the exhausts depending on the 'type of enginc an d the work it is intcnd ed to do. Do not go too narrow on the exhaust valve seats with an engine that has to deliver full power for long periods at a time. Some engines are fitted with hard seat inse rts. T hese inserts are usually made of chill ed cas t iron or tool stcel and ca n take a terrifi c punishment. However, be sure that they are fitted correctl y, beca use when they come adrift at high speed thcy can crea te Ill uch havoc, espec ially in an overhead va Ive engin e.

Page 32

SEAT GRINDING Valve seats and Ydlve head s should be reground with good equipment. Important is the condition of the valve guide since it positions the pilot of the grinding wheel or cutter. Most L-head competition cn gjlle~ have th eir illtake va lvc SC

the mixture a little on the ri ch side. An alcohol burning engine runs cool which is easy on the valves. Always remember that fuel is cheaper than engine parts. Summarizing: valve reliability can be improved by keeping the

valves and sea ts as cool as is practically poss ibie. Excessive ru st formation in the water jackets and steam pockets caused by stagnant water impede the flow of heat from the metal to the cooling water, causing local hot spots and di stortio n . Another important point is using the correc t type of head gasket, and always make sure that the cooling wa ter holes match those of the block and head . If cooling water nozzles or distributing tubes are used make sure that they are install ed correctly and last but not least : the radiator must be efficient and of the correct type.

MAXIMUM VALVE EFFICIENCY

The foll owing suggestions IllJY prove helpful in attlining max imum gas Aow past the va lve. As we already s tre s.~ed , the valve seats should be as narrow as possible commensura te with reasonable reliability. Furthermore, the va lve heael should be just ,1 Iittlc larger than th e outer diamctcr of its sca t. III S(lIll C instances it is ad va ntageo ll s to undercut th e va lve heads. ll owcver this cxpedient lllust bc Zl pproached carefull y to prevent wClkening the valve undul y. If oversizc va lves arc fitted it sometimes pays to open out thc combustion chambcr (0 11 ohv engines) around the vJ lve heJd to prevcnt masking or shrouding of the valve. Relieving of th e block is important on Aathead engines. Finall y, a 30 degree va lve sca t is considered to have slightly better gas-Aow characteri stics than a 45 dcgree sea t (especially with L-head engines).

Torque, Horsepower and Dynamometer Testing

TORQUE AND HORSEPOWER It may not be out of placc to ha ve a little discussion on the meaning of the term "torque" a\ld its true relationship to the powcr output of an engin e. It has been our experience that there is a lot of confu sion on th is score. Engine outp ut as we all know is expressed in brake horse power

(bhp ) . It is ca lled "brake" horse power because it is meJsured by "braking" the power output shaft ( the crankshaft usually) oil a device called the dynamometer.

Page 34

Without gO ll1 g into confu sing details, let' s state here and now that torque simply is a force, but always connected with a rotation. Everything that rotates is produced by torque. Technically, torque is expressed in pound-feet (Ib-ft ) which denotes the turning or twisting effort exerted about a center of rotation. If we apply a force of 30 pounds on the end of a wrench two feet long (say to tighten a nut ) th en we are exerting a torque of 30 x 2 = 60 lb-ft. This is the way torque wrenches are calibrated .

In the case of an internal combustion engine, the two factors that determine the horsepower output are torque and rpm. Mathematically this relationship is expressed in the simple formula:

T x rpm r HP =~ (r stands for torque ) .

This formula indicates that the horsepower output of an engine is proportional to both torque and rpm, which after all is only logica l.

DYNAMOMETER TESTING All we do when tes ting an engine for output on a dynamometer is measure its torque by putting a load on thc output shaft . In doing this test, the engine is run at full throttle and the dynamometer load ad justed in such a way to hold the eng inc rpm at the desired figure. (It is important to keep in mind that the engine rpm is governed purely by the dynamometer load and not by the engine throttlel. By measuring this full throttle torque at different speeds, with increments of, say 500 rpm , an cngine torque curve can be drawn up, and with th e help of our horsepower formula it is easy to ca lculate and draw the horsepower curve.

TORQUE AND RPM The foregoing illustrates th at torque or rpm as a single factor do not mean a th ing; it is only the combination of these two fac tors that enables us to properly evaluate the performance characteristics of a given engine. An engine that procl uces a lot of torque at very low speeds (by gea ring clown ) may be just as useless for our purpose as an engine that spins at ast ronomical speeds without hav ing any torque to spare for propulsion . If we study the accompanying power output and torque curves

we' ll notice that the peak of the torque curve does not coincide with the peak of the horsepower curve. It should not be too difficult to understand why this is so. We know that the power output is pro portional to both engllle speed and torque. Now if the rate of increase in rpm overrules the rate of decrease in torque, we are still gaining and power is still going up . T he horsepower peak is reached whcn th e r

I I'

! II

WHAT KIND OF TORQUE CURVE One of the main factors determi ning the n,ltme of the torqlle cune is the camshaft. A 1l1ild camsh8ft wi ll givc plcnh of pulling pO\I"Cf (to rque ) low dO\vn; a radical call1s1uft wili only perform lIear th e top end . it al1 depends on the purpose that our engin e wi l1 be 115('(1 for as

to lI'il,lt the torquc curve should look like. General1 y spelli ng th ollgh, al1 re,111l potent eO!11 petitlon engines should be set up so that the), develop their 11l8ximum pO\ler nC,Ir the top end , not beGluse we especial1\' like it that 11,11 but becdllse it is inevitable. .It is of course ven n icc to set 1I p om engi li e in sll ch ;1 IV

THE FIELD OF CAM DESION ... working up to the POLYDYNE

Basically, the principle of the camshaft is to open and close the valves in the correct sequence. I n the Otto four-cycle this sequence is timed in relation to the crankshaft and thus the piston. What is being done by the camshaft is to "trap" the greatest possible weight of airgas mixture in the cylinder, or to try and approach 100 per cent volumetric efficiency.

Now as everyone knows, nothing starts to move instantaneously, nor stop instantaneously. This propery of matter is known as inertia. If it were not for the inertia of the gasair mixture , all engines would be timed to open intake valves and close exhaust valves at T.D.C ., and open exhaust and close intakes at B.D.C. ; "nd no matter what R.P.M. the engine turned, 100 per cent volumetric efficiency would be attained. Now the average " hot-rodder" knows that this just does not work. He is well aware of "supercharging," ramming and is becoming more acquainted with the camshaft through the educational information furnished him by cam manufacturers interested in progress, and not just making money off the "hotrodder." He has become aware that the exhaust opens before B.D.C. and closes after T.D.C . to take advantage of the inertia of the gas-air mixture, to give greater volumetric efficiency as the R.P.M.'s of the engine increase.

Therefore, he has bought camshafts which gave him the timing he wanted, or if he did not know, he had faith in the integrity of the cam manufacturer, told him his problem, and bought the shaft recommended. Thus, the application determined the names for some camshafts; i.e ., 3/4 race , full race, and track grinds. The average "hot-rodder" soon learned that one manufacturer's 3/4 race cam was better than another's, that there was more to a camshaft than a name. Consequently, the most common question asked by a "hot-rodder" about a camshaft is, "Is it as good as an 'Iskenderian' "? This can be answered only o~e way - "No" - because a camshaft cannot be copied from a model cam with a machine that traces. I n order to make a camshaft correctly, the cam is started as a mathematical expression to which must be added the tolerances allowed for manufacturing. Thus , with such mathematical expressions as a cycloidal cam when used for high spet;d camshafts the mathematical contour must not vary more than .0003" from the true value at the start and at the top. Therefore, if the cam manufacturer makes a shaft within the tolerance on the high side, and the "bootlegger" copies this cam, chances are he wilt add to this tolerance and his final product will have no resemblance to what he tried to copy. Also, he may remove more stock and the results would be the same - an inferior camshaft.

What we have discussed will now be brought more into focus in relation to camshafts. Inertia , which applies to gas flow through the induction system, also applies to the camshaft. One instant the valve is seated, the next instant the valve has started to move . As it moves off the seats it increases its velocity until it reaches its peak; then it slows down to a stop when it is fully open . From here it goes through the reverse process of opening or the process of closing. If in opening, the valve is accelerated too fast it does not follow the command of 1he cam, but leaves the cam and at a

Page 38

Xli

later period rams back into the cam; this is what we call "float." To overcome this the accepted practice has been to increase the valve spring pressure to hold the tappet in contact with the cam at all times. This worked fairly well , but as spring pressures increased it was soon found that camshafts and tappets wore out.

The above describes the two conditions that the cam designer must work to satisfy. The thermodynamic problem of getting the greatest possible charge of the gas-air mixture into the cylinder to do work on the piston, and the equally important kinematic condition of holding the valve train together at the desired R.P .M. range at which the engine is to operate.

The early camshafts used contours which were of two families; the Simple polynomial and the trigonometric. It was soon found that the trigohometric curves were superior to the polynomial curves. They gave smoother action to the valves, were easier to manufacture, gave less vibration, wear, stresses, nOiss, and tool( less torque to turn. The basic equation for this family of curves is L = Can

When L = Lift n = any number C = A constant 6 = the angle in radions

In this family we have the following curves, 1. a straight line n = 1 2. a parabolic or constant acceleration n =2 3. a cubic or constant jerk n = 3

For your information, if you shOUld desire to try any of the above curves the formulas are given below, The curves of the trigonometric family are the simple harmonic, which has a cosine acceleration curve, the cycloidal, which has a sine acceleration curve , the double harmoni c curve which is composed of the difference between two simple harmoniC curves, one being onequarter of the amplitude and twice the frequency of the other, and the elliptical curve. The contour of the elliptical curve depends on the relationship of the major and minor axes . As the horizontal axis becomes larger the velocity at the start and stop become slower. If the horizontal axis is zero the contour is the same as a straight line . At a ratio of 11,8 the elliptical curve approaches a parabolic curve .

L. Straight line = h6 = L B

2. Circula( Arc = H - [H2 -- (Rp e2)r12 L 3. Simple Harmonic = ';' (1 - cos n6 = L

B

2n6,14. Double Harmonic = ~ [(I-COS nBej - 1/4(1 - cos S)J L 5. Cycloidal =.!!. ( n6 - 1/2 sin 2n6) = L

n B B h maximum lift desired B cam angle of rotation to give maximum lift, radions w cam angular velocity, radions/sec. B cam angle rotation for tappet lift H radius of circular arc in inches R radius of pitch circle in inches LP Iitt

Page 39

h external load acting on follower, Ibs. All of these curves, both the polynomial and the trigonometric were used with the addition of cams composed of circular arcs. Also, combinations of SI initial compression spring force with mass m at zer.o position, lb.

curves were used to overcome the inherent bad characteristics of each. N cam speed, RPM

Some success was obtained, but no completely satisfactory cam design was yt; I ift of cam , inches. Th is is not the same as y because of the

accomplished linkage deflection.

I y lift of valve, inches. With the advent of the overhead valve engines, more troubles were encountered and it was finally realized that besides being a thermodynamic ~ cam angle of rotation for valve lift, y, degrees and kinematic problem of designing a satisfactory cam, it was also a

Now, when a mass m is subjected to an acceleration such that at anydynamic problem, which required investigations into the masses, accelera ! instant tions, and elasticities of tappets, push-rods, rocker arms, and springs. d2y

Forces = m -2 (1 )

Finally, the "Polydyne" cam arrived which combines the polynomial equa dt

tion with the dynamics of the valve train . This cam recognizes that much The forces acting are

faulty operation of high speed, highly flexible systems can be attributed to Main spring force = ksY External load = - Lthe difference between what the cam commands the valve to do and what

Linkage force = -kf(Y - Yc) Init ial spring force = -SIthe valve actually does. The difference in action between the cam and

the valve is basically due to elasticity in the valve train; i.e., the com Substituting in equation (1) gives

ponents act as springs of various stiffnesses. Thus, it cannot be assumed d2y

-ksy- L-Sl-kf(y-yc) = m that the valve of an automotive valve train has the same movement as the dt2

cam profile. Solving for cam lift,

POLYDYNE CAM yc = L f SI kf r kis md 2.y

In the "Polydyne" cam for the first time we design the cam shape to give -.- f ~ y,L (2) k f dt2the desired valve action . This cam system of cam design recognizes that flexibillity cannot be reduced or eliminated. In equation (2) it is convenient to change the independent variable from

time t to the cam angle B; degrees. Usually the cam profile is given as a Basic Advantages: function of angle ~ in the form :

l. By direct means it can el iminate "float" . y = f(~) inches 2. By direct calculation it provides the only means of controlling the Or the cam lift is a fun ction of the angle. Therefore, to find the velocity

exact position of the valve. and acceleration with respe ct to time, 3. It limits vibrations to minimum amplitudes if run at the design v - dy/ dt = dG/ dt X dy/ dG = w(dy/ dG) inches/ sec.

speed .

and

Primary Detriments:

a = d2Y/ dt2 = d2G/dt2 X d2Y/ c'()2 - w2 (d2Y/do2)inches/ sec. 2 1. It requires a high accuracy in manufacturing to realize the advan

tage of the mathematically computed curve. w = cam angular velocity, radians/sec.

2. The mathematical work is momentous and laborious unless a high Substituting wLdLy/ dS2 for d2Y/ dt2 gives

I speed computer is available to do the mathematical calculat ions.

d2Y/dt2 = (360)2 ( ~)2 X (....L)2 x (ID 2 x d2y/ dG2 rev 61:) sec.

In the following, a typi cal example indicating the method of attack estab

lishing the basic equations for a high-speed cam valve system will be = 360 N2 d2y/ W

followed through . First, let us determine the flexibility relationship of the = 36 N2 y"

tinkage . Any valve train may be divided into the usual dynamic equivalent Substituting in equation (2) yields the cam lift system of four parts.

Yc = I. ,L S 1 l' kf / ks y';' !ll x 36N 2y"

l. Compression Spring - to hold the tappet on the cam.

-kf- kf kt 2. An Equivalent Mass at the end of the valve train . Rewriting,

3_ A Spring representing the combined elasticity of the I'inkage. Yc = ra -I kry / cy" (3) 4. A Cam.

This you will recognize as the equation used in an ad in "Hot Rod" The notations used in the calculations are: magazine. In equation (3) r. = rs / rk == the ramp height, in inches. This

ks spring rate of compression spring, Ibs. / in. is the initial deflection of the valve train to eliminate (1) pteload, and (2) clearance , so that motion of the valve is impending. kf = spring rate of follower linkage Ibs. / in.

m 12g = equivalent mass at the follower end, Ibs.-sec. ji,n.

rs = L tf SI = initial static deflection of train , inches

w equivalent weight at tappet end, Ibs.

Page 41Page 40 \llll

r k = clearance in valve train, inches

kr = Kf ~f ks = equivalent spring rate ratio of the valve train. m x 36N2 .

c = k = dynamic constant, degreesf

Equation (3) may be applied in either of two ways: 1. Having an arbitrary cam profile Yc, the actual motion of the valve

end may be found. This method may be used to investigate exist. ing cam mechanisms.

2. A suitable valve motion versus cam angle may be assumed, and the cam profile may be developed to fulfill that motion at the desired soeed.

Now we \'VIII try to explain some of the terms used in equation (3) in less mathematical terms : r a = ramp height: The ramp is a small "pre.cam" and is of critical importance. Its function in height is to compensate for the deflection of the valve train due to the clearance rk and the static deflection rs ' It is the amount that the cam will deflect the linkage be. fore the valve moves, opposing the preload in the compression spring holding the tappet on the cam. In highspeed overhead valve engines with highly flexible pushrods, the clearance rk is small as compared with the static deflection rs' The ramp height may be found by measurement on the actual engine; if a micrometer indicator is put on the valve and an. other on the tappet and both are set at zero when all mechanical clEar. ances are taken up by a screw or small hydraulic jack; if you continue to jack the tappet up until the indicator on the valve indicates motion you have determined the ramp height due to deflection of the system on the indicator on the tappet : This is rs' Since the external load is often constant and the rigidity of the system is made as large as is permis. sible, the ramp size is primarily a function of the initial spring load.

The second term of equation (3) is the cunstant kr' or the equivalent spring rate ratio, which is related to the stiffnesses of the valve train linkage kf ' and the load spring ks ' Every part in the system acts as a spring of different stiffness. Therefore, the follower linkage spring rate kf in an engine consists of the sum of many individual springs such as: the bending of pushrods and rocker arm shafts, the deflection and twisting of rocker arms, the deflection of bearings, and the deflection of cam and tappet surfaces.

The most convenient and accurate method for determining the overall value of kf is by measurement on the actual engine. This can be done by loading the system and accurately observing the deflection with a micrometer indicator. These values when plotted approximate a straight line. The spring rate kf equals the slope of the plotted line. The compres. sion spring rigidity ks' may easily be found from the spring manufacturer or from engine manufacturers' service manuals.

The last part of equation (3) contains the dynamic constant - c:

c = 36 kfm - N 2 which can be rewritten as

\'V 2 c = .093 if N where w = equivalent weight at follower end , Ibs.

Page 42

In this respect we must consider the effect of the rocker arm ratio on the equivalent weight. This weight w mayor may not be the total weight of the members. The following are suggestions for finding the equivalent weight W: For long thin pushrods that act as springs and actual com pression springs, we do not use their weights directly. Theory has shown that about onethird of their actual weight is effective . This is because flexibility prevents all the mass from being accelerated at the same rate . Thus, the acceleration wave does not affect the other twothirds of the weight.

Almost all v, our present engines use rocker-arms to multiply tne action of the cani. This influences the cam design. A lever with unequal arms has its effective weight inversely related to the square of its lever arm ratio. If we have a rocker arm wittt arms d'l and d2 , the follower veloci ties VI and V2, and a weight w, to be referred to the valve end . The kinetic energy of weight WI is:

V2K E = -1.. ~ . ? g 1

This must equal tne kinetic energy of the equivalent weight on the valve end.

v2K E -.l.. w . - 2 g 2

Equating gives: w WI ( :~ ) 2 WI V2 the equivalent weight where V = rocker arm ratio

Now that we have explained how the " Polydyne" t:4tJatlon IS arrived at, what the terms in the equation mean , and how to obtain them, we will try and expla in how to use it. Equation (3) is the equation for cam lift:

Yc = r a / kry / cy" (3) Differentiating with respect to 0, yields for the cam,

Velocity yc' = kry' / cy'" (4) Acceleration = yc" =" krY / cy I V (5)

The first four derivatives of the follower motion equation. y = f (0) must be continuous functions. This is required . since we desire to maintain con tinuity of the cam profile Yc . velocity Yc. and acr.eleration Yc" . Equation (5) shows that the cam acceleration y", is a function of the fourth deriva tive of the follower motion. ylV. Thus, combinations of basic curves can not be used, since they are discontinuous in these higher derivatives. However, polynomial equations are feasible. These equations may be used to fulfill continuity in any derivative Simply by adding power parts to the fundamental equation.

Cn9fly = Co / C1sZ / C3e3 / Thus. the procedure for design of a "Polydyne" cam is as follows:

1. I,;hoose a poiynomial equation, y = f(~) with proper control at the end points .

2. Establisn the valve system flexibility relationship. using equation (3).

3. Combine (1) and (2). plot displacement. velocity, and acceleration curves of both the cam and the valve end to check the reasonable ness of the choice of the polynomial in (1).

Page 43

Theoretically, if we run the " Polydyne" cam system at the designed speed, the action will have no vibrations . Thus, a cam could be designed for engine speeds of 10, 20, or 30 thousand R.P.M.'s and thf valves woulCl not "float." Actually, small amplitude vibrations (at the natural frequency of the system) are evident in operation. These may be due to the surface inaccuracies, and the application of the external load.

'II If t he 4-5-6-7 po lynomi al were used in its simplest form for a cam design the equation would be:

LI FT = 1-35&4 -f 84&5 - 70ai t- 20(17 VELOCITY = 140tP + 42004 - 42e~ + 140&6 ACCELERATION = 420&,2 -f Ibl:SOeJ - 210e5 + 84005

JERKS = 840&+ 50409'2 - 8400e3 --f 420004

Each of these eq uat ions would have to be solved for each degree that the cam profile moves the valve train . Assuming a cam of 280 0 duration with a ram p of of crank travel. each of the se equations would have to be30 0

solved 85 times. Therefore , you can see why it is next to impossible to design these cam s without the aid of a computer. Al so, in internal com. bustion engines t he expone nt s are much hi ghe r t han t hose of the equations we have in the 45-67 polynomial listed above . Th ey are more likely to be 2738-29-30. Now anyone knows how laborious it is to multiply the same number by itself 30 time s even when it i s le ss t han 10. Just think how laborious it would be if the number were such as 126.

In conclusion it is obvious from the preceding explanation that a great deal of hard detailed work is necessa ry to design the proper cam for some specific need of an engine. It is also self evi dent that it is impossible to copy these profiles accurately unless the original mathematical operations are known. Furthermore the camshaft grind ing equipment must be the very finest and most accurate in order to produce the close tolerances required to make a polydyne camshaft,

The mathemati cal solutions required in optimiZed cam design are so laborious that an elect roni c computor is necessary to achieve an accurate solution. It has been conservatively estimated that an optimized cam design so lution requires about 150,000 to 200,000 arithmetic ca lculations. With a desk ca lculator these would take about 75 man month s.

THE POLYDYNE PROFILES ARE BEING INCORPORATED INTO ALL ISK END ERIAN CAMS.

I" Page 44

HOW TO DETERMINE TDC ACCURATELY (See following page for working procedure) The correct determination of top dead center (TDC ) of th e engine is the starting point of all timing procedures and it is therefore very important tha t w e locate this point with the utmost accuracy. Due to the fact that piston movement is very slight with respect to crank rohl tion at TDC, it is very casy to miss this point hy a few degrees if speelal care is not taken. T wo important itcms that have to be uscd in this proceclure arc J

dial indicator and ,1Il accurate degree pbte (also c lllcd timing disc) . The degrec pla te should be accurately b stelled to th e front of the crank in such a way that it is concentric with the centerlill c of the crank . \\ 'c al so have to have a stationary pointer (a sturd y metal strip or hClv\ wire ) v.:hich must be securely bolted to a conveni ent pbce on the c\'ll1lclcrbl ock. Now l'nOUJ1t th e dial indicator to a evlindcrhead stud in slleh a

wa y that th e indicator stelll point res t ve;tiealh' on th e center of tile piston crown. The dial indicator should bc Ijositioned \() th;lt the indicator hand moves th rough approx im

"t~/

How To Find ...

ABSOLUTE TOP DEAD CENTER It is a common error to miss top dead center (T.D.C,) by a few degrees due to the piston dwell at this point. Inasmuch as this inacc uracy will substant ially affect subsequent timing, the following procedure is suggested to correct this error.

1. Mount degree wheel or degree plate on the front of the rrankshaft. Now bolt a stationary pointer on the cylinder block. (See illustration.) Pointer can be made of metal strip or heavy wire.

"~~

Dial Indicator ,. "

/Degree Plate

2. Mount a dial indicator secure ly to the cylinder block. Now adjust dial so that at maximum piston rise the indicator sweep hand travel s through approx. ,025" of movement. The dial indicator contact point should rest on the center of the piston.

3. Now to turn crankshaft over use a long handle wrench or lever so as to get an ev~n, steady movement- and not a je rk y motion. Somet ime s a round steel bar can be inserted into the crankshaft balancing holes to rotate the crankshaft. The crankshaft should always be rotated in the normal running direction.

4. Holding your thumb down on No. 1 piston (to eliminate all lash) come up slowly to T.D.C, until you reach what you gue ss to be the middle of T.D.C. dwell. Set your stationary pointer at T.D.C. on the degree plate.

5. Now rotate cran~shaft one more revolution and this time on the way up to T,D.C. stop exactly .020" (d ial indicator reading) below the maximum piston travel which is T.D.C. For example, say it reads 10 degrees before T,D,C, Continue slowly on up to T.D.C. over the hump and down the other side, keeping thumb firmly on piston. Watch dial indica tor closely, and when it reads exactly .020" down from T,D,C., stop and note reading on degree plate. If you have a perfectly split overlap it should read 10 degrees after T.D.C. If it doesn't you have not hit T.D.C. exactly and must try again.

Making Corrections :

Split the difference (your error in degrees) by either bending the pointer sl ightly or moving the degree plate radially on the crankshaft. After you have made the adjustment come around with the crankshaft as before, stopping .020" below each side of T.D.C. When you get exactly the same degree readings .020" below each side of T.D.C, you have found absolute top dead center.

Page 46

....

Procedure For CheckingValve Overlap Without Dial Indicator

or Degree Plate Sometimes an occasion arises where it is necessary to make a spot check valve timing and no appropriate equipment is available. The following is a good procedure to follow in such case's,

Note: Although the following procedure pertains to Chevrolet engines it can also be applied in checking nearly any flat-head or OHV engine.

PROCEDURE: 1. Insert the ca mshaft and mesh the timing gears on the stock marks. Bolt the bronze thrust flange to the cy linder block. Do not, as yet, install the gear cover.

2. Usi ng a long wrench or lever turn the eng~ne over in the normal running direction. Use enough leverage so that you get an even, steady movement instead of a jerky motion . Rotate until the intake and exhaust valves on No. 1 cylinder are in the overlap position (both valves opened slightly). Stop exactly on top dead center (T,D,C.) which is marked UC on the fl ywheel. You are now exactly on T.D C" with the intake and exhaust valves opened slightl y.

3. Take screwdriver and box wrench and loosen the rocker arm adjusting screws until the intake and exhaust valves are ju st barely closed. Lock the tappet adjustment sc rew so that the intake and exhaust valves are at exactly zero clearance.

4. Now turn the engine over again exactly one turn at the crankshaft to UC on the flywheel. You are now at T.D.C, on the compression or firing stroke,

5. De termine the amount of gap between valve stems and rocker arms on intake and ex haust valves as this will give you the actual amount of valve opening at T.D.C. at overlap time (less, of course, tappet se tting). To accurately measure this gap use regular feeler gauges of various thicknesses added together. Compute total amount of gap and record on a piece of paper. If the amount of gap on intake and exhaust is exactly the same you have an exactly sp lit overlap. However, if they are within about .005" of being identical this cou ld be considered close enough for a split overlap.

EXAMPLE % CAM Advanced Cam Position: If your intake happens to come out with .050" gap and the exhaust with say .020" gap,

your cam is in an advance position. In this position the cam will produce more low speed

power or torque. However, there will be a subsequent loss of power at high RPM.

Retarded Cam Position: If, on the other hand, the intake came out with .020" gap and the exhaust at .050" your

cam is in a retarded position. In this position there will be some loss in low speed torque

and power and some subsequent gain in high speed power.

Split Overlap : If intake and exhaust gap comes out exactly even or within .005" of each other you have

a sp lit overlap, Generally speaking all racing cams run best in the split overlap position.

While there are exceptions to th is rule it is usually best of all around performance.

Page 47

POSITIVE STOP METHOD OF FINDING Tee

Another convcnient method of finding TOC can be performed as follows : as in the previous method affix the degree plate onto the crankshaft but not necessarily to what we est imated to be T OC. The ncxt thing we' ll take is

Top Tuners Tip~

Thc 8clv;l11 tage of fol1 owing th e procedurc outl incd above is that our 110 lllC-1l1

VALVE LASH AN D VALVE TIMING If the behavior of the engine indicates that th e va lve timing is too long (for a particula r competition event ) it is entirely possible to calm the timing clown a little bit by in creasing the vdlve lash. T his has a twofold effect: in the first place it "shortcns" thc timing (less duration) and secondly, it slightly speeds up the va lvc action (quicker lift ).

HYPOTHETICAL OHV ENGINE WRONG CORRECT

=,~I iZ~~1 I }-==~200 1 ~ Ij?

1001 .~,.. .. ,l... d.~~

-4--~4--t~~t--r

j/ 1 ~ .,4.-~150f---I-/ I . ~~J

L: 0000

3..

izsol l L.~ 4'"

Top Tuners Tips

The exhaust valve would open 75 degrees before BOC and close 35 degrees after TOC, also having a duration of 290 degrees . This setting then would give a "long" timing with a 70 degree valve overlap. The characteristics of this cam with the above setting would be: high torque and bhp in the top range; less torque in the lower speeds, and quiet tappets. This camshaft would be su itable for long, fast and slick tracks where high speed is most importan t. I t could also be used for drags if we remember to keep the engine high up in the speed range.

INCREASING TAPPET CLEARANCE SHORTENS THE TIMING Should we des ire to "shorten" the timing a little, we could open up the valve lash to say .025 in ., which would give the cam in our example a timing of 30, 30 and 70, 70 as shown in the illustration. This ad;ust-

T/!C

' ,,""IKE E){HAi/ST, TDe INTAkE EXHAusrOPENS CLOSES OPENS CLOSES

EXIUWST "XHAUSTOPENS opeNS

. 018 ,-" r "lPPET .O~5 i" TAJ>PFr

soc CLEARANCECLE"" "NCE BDC

ment has shortened the duration of the cam to 280 degrees and the overlap to 60 degrees. Theoretically there is some loss of valve lift (on account of increased valve lash ) but the inAuence of this is so slight that it can be neglected for practical purposes, and it is partly offset by the quicker valve action . The charac teristics of this se tting would be: less torque and bhp in the top range, but more torque in the lower speeds, resulting in a more fle xible engine .

Using wider clearance than specified will also cause the point of the valve float to occur at a lower rpm. Care must be taken that the engine is not run to the point of valve float. There will be some tappet noise. This setting is recommended on a heavy dirt track and on short tracks where good lugging power is required out of tight corners. The increased clearances are harder on the valve gear but will not be harmful providing that it is not overdone.

Summarizing: altering the tappet clearance in the main has a twofold effect: firstly a variation of duration of valve opening and secondly, a variation of the rate of va lve lift. (We already mentioned that the very small variation in actual valve lift can be neglected.)

Page 54

VALVE TIMING for TOP PERFORMANCE Sig Erson, shop foreman at Iskenderian Racing Cams in Inglewood, Calif., denio onstrating the correct way to chec k the valve timing of Chevrolet va engine . Valve timing checks aren't too diff icult to do but they must be made right if they are to be of any value .

NOTE: Prior to wr iti ng t his article Don Francisco spen t considerab le time in ou r plant , working in close cooperat ion with members of our staff. Art icle

Hot rodders who know enough abo ut engines to be ahle to take them apart and rea~scmble them correctly know

that valve timing is important to the way an engine will run, Ho\\"ever, anyone who would het tha t ninety-nine perc ent of the fell ows in this group don't know how to acc ura tely check the va ll 'e timing of thcir engines would have an excellent chance of taking horne t he lool.

The purpose of checking \'a lve ti ming is to dctermine whether the camshaft is insta ll ed in its co rrect relationship with the crankshaft. When this relationship is co rrecl. the a rea unde r the lift cUn'e, of the va Ives will be timed correc tly with lhe d isplacem ent curves of the cy linders . /'.. lift curvc for a valve is ma de by plo tting on graph paper the position o f its hcad in thousa ndths of an in ch liit off its sea l pe r deg ree of cranksh:lfl rO(;1lion , A di splacement cune ior a cy linder is plotted in the sa me manne r but it in voh"es movement of the piston in thousa ndths of an inch pe r deg rce o f cranksha ft rotalion, \V hen the vahes are limed correct ly, the lines of the t\\'o curves will coincide at the correct po ints when onc- cun'e is s upe rimposed on the ot her.

Va lve timing vari es for diffe rent cam grinds but a large percentage o f grinds are design ed to pro\ide "splil ovcrl ap. O\"erlap is the number of cranksha ft de grees of rota ti on the intake a nd exhaust vahes for a specifi c cylinder a re open at the same time a t the cnd of exhaust st rokes, O"erlap is split when the intake \'a lve opens thc samc number o f degrees before top dead cente r piston position tha t the exhaus l va lve closes aftc r top dead cenler. When the numher of deg rees the intake "ah"e opens befo re top center is

was reproduced in full in HOT ROD MAGAZINE.

greale r than the number of deg rees a l

which the exhaust ,ahe closes. t he timing

is sa id to be advanced. When the number

of degrees at which the intake va lve opens

is less than the number of degrees at

which the exh8ust valve closes, t he tim

ing of the ellgine is sa id to be retarded,

An cxception to the split timing condi

tion described would be when the "dura

tion' o f the intake a nd exhaust va lves

differ. Duration is the number of deg rees

of crankshaft rotat ion a va lve is open

for each of its cycles. Camsha fts ground

to prov ide uncqual duration a re ca ll ed

" twopatte rn " shafts . Methods of COI11 paring Ihe dural ion of the intake and

exha ust va lves in a n eng ine for va lve

timing purposes and determining the splil

overbp pos ition for a t,,o-pattern cam

sha ft are described later .

One reason valve timing ha s an inl1uence on an enJ;incs performance is its effect on thc ' reve rse pUl11ping action" in the engi ne's cylinders at the beg inning o f comprcss ion st rok es. Because an inta ke valve closes after its p iston has sta rt ed its compress ion st roke. some .o f the iresh iue l an d a ir mixtu re that was ind ucted into the cylinder on the preceding intake stroke is forced out of the cy linder past the open v al ve. The closing time o f lhe intake va lve becomes. there fo re. one o f the factors that determines the quantity of fresh mixture in a cy lindcr when the va lve closes. Increasing the q ua nti ty of m ixt ure raises compres~ion and com bust ion pressures and decreas ing it lo\\'e rs the p res sures. An engine 's torque a nd horsepower outputs a re dependenl on these pressures; they ri se an d fall as the p ressures rise and fall.

Page 55

.....

Above lett: Dial .i nd icator can be used instead of positive StOP for find ing top center piston pOSi ti on. Care must be ex erci sed. Not recommended for amateu r me chanics. Above Right : Tool made from a spa rk plug and screwed Into one of the plug holes can be used as pis ton stop when a head is on the engine.

From the explanation ot the effects of reverse pumping act ion one might conclude that an engine would deli ver its maximum torque and horsepower outputs when it had a camshaft that closed its intake va lves precisely at the end of in take strokes. This is not true. Although such a camshaft would provide good lowspeed perfo rmance, performance at high cranksha ft speeds would be limited by the inabi l ity o f the cylinders to take advantage of the inertia bui lt up in their intake passages during intake st rokes. If the intake va lve clos ing time is delayed, th is ine r tia will cont inue to force fresh mixture into the cyl inders after the pistons have started their C-

lends inlo the cylinder. The flange that extends inlo the cylinder is shortened so that its lower end will be approximately ~ quarter o f an inch below the top surface of the cy linder b lock when the tool is in place .

A device for rotati ng the cranksha ft can be made so t hat it will attach to ei ther the front or rea r end of the shaft but it must be long enough to provide sul"li(ient leve rage so that the shafl can be turned slowly a nd evenly, as littl e as a degree at a time when necess,'t ry. Complete contro l of 'c rankshaft rotation is nelessary for accurate va lve liming chelks hec luse of the sma ll amo unlS o f crank,ha fl and v~h'e movemen t invo lved. Things that can ca use. valve timing to

di ffe r frolll whal it should be are numernu , hu l those t ha l should be checked ~nd (Orrected before a camshaft i, insta ll ed in an eng ine are the st raigh lness of the sha ft itself. the condition of the camshaft bearings in the cy linder block. and the conditions of the sprockets and cha in . o r gears. that wi ll dr ive the shaft.

A benl camshaf t can throw va lve t im ing off bad ly. Reground camsha fts are checked for slraightness and straightened as necessary between the machining and grinding operations they must go through but it is ent irely poss ible for one that left the g rinder's in a st ra ight condition to be bent or sagged by the time it reaches the customer. A sagged sha ft is one in wh ich the journal runout becomes progress ive ly g-re,lter from the end journals to the middle journal. The most common causes of bent or sa~ged conditions are rough handling during shipment and s tresses rema ining in the shafts from the many machining and g rinding operations that lIere done on them .

A sha ft can be checked fo r straightness by supporting it between centers in a lathe or on V-blocks so that it can be rota ted . If V-blocks are used, they should be placed under the s haft's end bea ring journal>. Runout of the sha ft 's intermediate journals. which is the indication of a sagged or bent condition. is then lI1easured with a dial indicalor supported sO tha t its plunge r rests on the journals as the sha ft is rotated .

A sagged shaft is st raightened by exert ing a light pressure on the co rrec t side of the shaft's middle bearing journal with a press or some other de"ice wh ile the shaft is s upported by its end journals. H owever, this job shouldn't be attempted by any-

Page 58

Graph shows the piston di splacement for one cyli nder, lift diagrams for both valve s. Points where the CUNes overlap indicate the valve timing condition for cylinder.

one who isn't famil ia r with the r isk involved. A ca~ t camshaft. of the type used in mos t modern automohile engines. wil l break like a piece of glass if too much pressure is exerted on it duri ng a st raightening process. M en who regrind camshafts know the limitations of the materi'a! used in them and how to straighten them sa fely. Un less you want to take a chance on coming oUl on the short end with a twop iece camshaft you can' t use, re turn a bent cast shaft to the reg rinder for s traigh tening .

Camsha fts mac hined from stee l bill e ts can be straightened without fear of their breaking but experience is required to do the job s uccess full y. It wou ld be safer , and probably cheaper in th e long run , to a lso return a steel s ha ft to the man who ground it for whatever straightening it needed . Camshaft bearings in the cylinder block

a re important to valve timing beca use it is their du ty to ho ld t.he camsha ft in its co rrect relationship with the valve lifters. Al so, they hold t he shaft in its correct pos ition i" relation to the cra nksha ft, whi ch is im porbnt to maintain ing the co rrect tension in the timing chain. Actua l clearances between t he bearings and the shaft 's journals can be determined by miking the inn er diameters of the bearings and the diamete rs of the bea ring journa ls on the s ha ft an d then comparing the diameter of eac h bearing- with its respective journal. C learances g reater than that a llowed by the spec ifi cations in the shop manual for the engine must be reduced by insta lling new bea ring inse rts in the b lock.

Worn s prockets and chains, or gears allow valve timing to become retarded because t hey let the camshaft lag behind

L.eft: While the degree wheel is on the crankshaft, check relation sh ip of the stock timing mark on the crankshaft pulley or damper with the pointer on the cylinder block front cover to determine whether the two indicate top dead center position when the piston in cylinder number one is actually at top cente r. Correcting any misalignment at this time will ensure a more accurate ignition timing se tting. Center: Method of measuring valve lift when tool that replaces the tappet isn't avail able. Indicator is rested on a clamp attached 10 the pu shrod rather than on rocke r arm. Right: Simple setup tor measuring tappet lift with dial indicator. These are' /skenderian roller tappets. A special tool is installed in place of the tappet to eliminate inslalla. tion of the cylinder head, rocke r arm , etc.

the cra nksha ft. This condition is cor lion of the tappets for t he cy linder's rected by insta lling a new sprocket and va lves becl use both o f them will be un th e chain assembly, o r new gears. as the case heels of their ca ms a nd . therefo re . in their may be. Available for some Chevy. Pon lowest position in the cy linder hlock. tiac. and Oldsmobi le engines are double With the piston at approximate: top row roller chain and sprocket assemblies dead center, ins tall the degree wheel. or than can be used in plJce of standard the degreed crank pullcy or tl ywhecl , and "silent link " c'hains and sprockets. R oller its pointer. :\ djust the pointer and the chai ns are made for truck eng ines and they wheel so that the pointer is in lin e with are supposed to be stronge r a nd have a the mark on the wheel that wi ll be used longcr useful life than silent li nk cha ins; for top dead ce nter piston position . 1

-~

III

, hould indiclt e when the pist on is aga inst the tool. .\djustinR th e whee l sion stroke, The intake va lve's tapret will ntow be on the heel o f its cam, where it must be when the dial indicato r is adjusted to nlign its pointer with its l.ern ma rk . After adjusting the indica tor, rota te the cra nkshaft in its normal direction to move the piston to the bottom of the cylinder and then approx imately three-qua rters of the way back up the cy linder. Always rota te the cra nksha ft in its normal direction when va lve timing

i ~ heing checked. This causes the conditions in the camshaft dri ving mecha nism 10 be the same as they arc when the en gine is running. If the t iming were checked hy rotatin~ the cra nkshafl in the direct ion opposi te normal rotation. the sJack in the chain. or clea rance between gears. would allow the relationshi p o f the ca mshaft to change from what it wou ld he when the engine was running. Continue turning the crankshaft slowly

until the lappet is liit ed enouj:!h to register a re"ding of .050-in ch. T hi s amount of t

1 aq

vanced or retarded one full tooth; how ever, the amount of advance or retard effected by one full tooth is so much that it is out of the question unless there is

somelhin~ drasLically wrong with the camsha ft or its dr iving members . To dete rm ine how many degrees one tooth (either camshaft or crankshaft- the result i, the same) changes the timing in a specific ~ ngine, divide the number of teeth in the cranksha ft sprocket or gear into 360 The nlethod of moving a shaft in its

sprocket , or gear. depends on how the driving member i, secured to the shaft lrankshaft sprockels and ~ears are nearly always keyed to their shaft but a camsha ft sprocket or gear can be either keyed or bolted. or both keyed and bolted. A keyed sha ft can be rotated in its driving memher by insta lling an offset key in it or by cutting a new key way in the driving member. At I skenderian 's. offset keys for this purpose arc available for so me makes of engines. A camsha ft that is bo lted to its sprocket III gear ~;J11 be rotated by I'j ling the origina l holes in the sprocket or I(("r obion/( or by drilling a new se t of hOles. II a ne w keyway is to be machined vr new capscrew holes are to be drilled, it. will be necessary to mo ve the new keyway or holes a few teeth from the original ones to eliminate interference between the two. This requires accurate laying-out of the new keyway o r holes to compensate for the number of teeth tbey are moved, plus or minus the amount the liming is to be changed. Something that must be remembered

when any method is u~ed to cha nge v~l ve timing is that one degree of elmshaft rotation is equa l to twO de/(rees of cr:lnkshaft rOla tion . for eve ry 360 degrees the cranksho ft roto tes , the camsha It rotates onl y I So decrees. The reason for this is that the el msh"ft rotates at an i v onehalf crankshaft speed ; it makes only onehd f as many revolut ions as the crankSh:lft. Therefore . to advance or retard the camshaft 8 degrees. for instance, the camshaft must be rotated in its sp rocket only 4 degrees. Another thing that must be remembered i:, that chain-d ri ven camsha ft s rotatc the SClme direc tion as the cranksha ft, and those dri ve n by gears rotate in the direction opposite that of the crankshaft .

It is imperalive t"a/. lite timing be rechecked after a correction ilels been made to guaranlee I"at lite desired results were obtained. If. for some reason or other. it be-

Page 62

...............

comes desirable to check the timing of morc than one cylinder. use the same degree wheel selling used for the fITst cylinder. Changil'/.( the wheel to COrrespond with the top center position for the piston in each cylinder wi ll cause any difference in the. relationship between the crankpins un the crankshaft to each othe r to affect the valve timing. Such a condition Can be corrected only by regrinding the crankpins to place them in thei r correct relationship . Actually, a shaft should be checked for this condition before it is installed in an engine. The cams on a precis ion-ground camsha ft are the specii"led number of degrees apart around the sha (t. Checking diffe rent cams with the same degree wheel setting . using different points on tht: wheel fo r top dead center marks tor the respective cy linde rs. checks thi s COII dition. Any method of checking valve timing

that requires lash clearances isn't recommended because of the rocker arm factor mentioned previous ly and also because lash clea rances a re difficul t to adjust correctly and even ly. Clearances that were too wide Or too close. or that were uneven, would cause the results o f the check to be inaccu rate. Anothe r p ractice that isn " recom

mended is that of changing valve lash clearances from those specified by the cam\ grinder to compensa te for uneven va lve timing . Correct clearances are necessary if the valves and the rest of the valve actuating parts are to have normal life expectanci es. Valves with too lillie clearance may be burned because they cannot remain on their seats as long as they should, Or because they are held open wh en they shoul d be closed. between opening cycle,. The tappets of valves that have too much clea ran ce may be off their ramps before they a re lifter! enough to take all the las h 'lut of the valve linkage and open their valves . Also, the Halves may close before the tat.>pets contact their clos ing ramps. Results of these conditions J re noisy valve action and the possibility of valve ~oat an d broken valve actuating parts.

After an engine has been run , it is necessary to check the timing of its valves from t ime to time to cietermine whether wear in the camshaft's driving members ha s allowed the liming to become retacded . The frequency of such checks will depend on how the engine is used. An allout compet ition engine would require more frequent checks than one used for nonnal driving .

BY TED FRYE

Correct spa rk lead can make the difference between being a winner and a loser; it can be re sponsible for adding more than a hundred horsepower to an engine without making any other changes; it can jump an enthusiast who consistently runs second and third up to Top Elim inator runs at every meet. And the achievement of correct spark lead does not entail the purchase of more equipment; it's merely a matter of correct adjustment of existing components.

Some have invested $1000 in a competiti on engine with everything close except the spark lead and derived only $500 worth of value from the modifications. Any engi ne capable of developing 400 horsepower can be off 5 degrees in t iming and lose over 70 horses. Thi s common occurrence is attributed to the fact tha t the average enthusiast just does not understand spa rk advance curves in the distributor or magneto. This chapter, then, is written for him. We shall endeavor to explain, step by step, the procedure for establishing exact TOC, how to time the engine and furnish a rough estimation for correct spark lead settings for all the current engines used for racing. An exact estimation, within one degree, is almost impossible to forecast for any particular engine, as each engine has its own id iosyn cra cies with variable effects on tim ing. A "rule of thumb," however, will definitely be established so that every engine builder will at least start out within 3 degrees of what may later develop to be the exact spark lead for his engine .

DETERMINING "TDC" ACCURATELY The correct determination of top dead center (TOC) of the engine is the starting

point of all timing procedures; it is therefore very important that we locate this point with the utmost accuracy. Due to the fact that piston movement is very slight with respect to crank rotation at TOC, it is very easy to miss this point by a few degrees if special care is not taken.

......

CORRECT SPARKLEAD

EDITOR'S NOTE:

For a more thorough and com

plete explanation on finding

TDC see Page 46

Degree plate (available from most speed shops) is shown after being adjusted to read zero degrees at stationary pOinter

at TOC.

EDITOR'S NOTE: Ted Frye is employed as a field representative for Iskenderian Cams. A noted engine builder and race r in his owo right he is one of the first members of the Bonnevilie 200 MPH Club. This is a condensation of a feature article that appeared in a natiooal periodical.

Page 63

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KNOWING YOUR SPARK LEAD Previous paragraphs covered the procedure for finding absolute TOC in order to

establish a foundation from which we can work to se t absolute timing on the ignition. The only way to accurate ly determine exact spark timing is on the engine itself .

Spark advance shoul d be checked on the engine under actual running conditions. One of the best tools for doing this is a standard timing light, and the battery-powered type is by far the most efficient.

.Now that we have establi shed absolute TOC on the dampener, or degree whe.el, we have the point from which to begin with the timing light. However, we will need more degree marks on the dampener than the factory furnishes. We will start by ca librating the pulley on the advance side up to 50 degrees.

The simplest way to do thi s is to measure the circumference of the pulley with a steel tape. As an example, let's say the pulley measures 18 in. in circumference. To establish ignition timing marks, we divide the circle into 36 equal parts; each segment will represent 10 degrees and correspond with a liz-in. measurement on the circumference of the pulley. Then , when the pulley is turned or rotated lj2 in. in respect to a stationary pointer, the crankshaft will have been rotated 10 degrees. Now transfer these marks - at least five of them - to the dampener, beginning with TOC and going to the advance side (to the right of TDC when looking at the nose of the crankshaftl. The transfer should be made with light scribe marks first; after rechecking for accuracy, they can be cut in permanently with a three-corner file.

With turning handles attached, the crankshaft has been turned until degree plate shows 40 degrees before TOC_ Distributor or magneto is set so that full advance will show pOints just ope ning at this pOint. Final check will be made with timing light.

Using two hands and long handles, the crankshaft can be accurately turnzd one Dr two degrees at a time while initial settings

are made.

Page 64

The dampener will then be tailored to the engine it will be working on and we have eliminated the possibilities of inaccuracies in keyways and in stamping the TOC mark' on the dampener.

Now we can begin setting the actual spark advance. Different type engines will function more efficiently with different advance settings. Wedge-type engines - Chevrolet, Oldsmobile, etc . - will put out more horsepower on gas or mild fuels with a total advance of 36 degrees. Engines with hemispherical combustion chambers - Chrys ler, DeSoto, Dodge, etc. - will need 40 degrees total advance for gasoline and 45 degrees foe alcohol or nitro-based fuel s. Aga in, this is a rule of thumb not to be construed as a positive setting for each ind.ividual engine that falls into one of the above categories. But it is a good place to begin and will usually be within a couple degrees of what will prove to be the ultimate for each of the named engines.

Many of today's engine builders use the Vertex magneto. With these I feel it is a good idea to have a separate degree plate on the magneto. Such an arrangement will facilitate making adjustments after TOC is established.

Now to se t the distributor or magneto. First the engine must be turned in its normal direction of rotation until # 1 piston is moving upward in the cylinder on the compression stroke. As it nears the top of the bore, watch the marks on the dampener, and continue turnin