2017 Early Production Arctic Cat Thundercat Turbo Once again, our great pal Tom Ferry of Arctic Adventures [SkiDoo and Arctic Cat] in Rosendale NY came through with an early production 2017 Thundercat for DTR evaluation, just like he did with the 2017 SkiDoo Etec 850 that we tested earlier. This 0 mile TCat had been on display in NYC at the NASDAQ opening bell with Arctic Cat CEO Christopher Metz last week. It was then dropped off at Arctic Adventures (close to NYC) to be picked up by Arctic Cat and returned to Thief River Falls. But since Tom Ferry had this sled, and as a great proponent of Arctic Cat performance wanted to see for himself, and hopefully share with the DTR members and the world, the A-B comparo between the Sidewinder and Thundercat. Remember—Cat people saw that last year's Arctic Cat ZR7000 was noticeably down on power compared to the identical (other than the ECU cal) Yamaha Viper, tested back to back here on the same day for last December's AmSnow/ DTR NY Shootout. As the result of that testing, there has been plenty of internet buzz regarding possible turbo ECU tuning variation from one brand to the other. However, both Yamaha and Arctic Cat engineering people are said to insist that 2017 turbo ECU tuning is identical for both brands. If so, after examining this data it’s likely that the Yamaha Sidewinder turbo preproduction demo sled that we tested in March had a more conservative tune for demo rides/ magazine testing. Or, did Arctic Cat marketing people expect Tom to bring the new Thundercat here, and fit it with a “hot” ECU? Conspiracy theorists can only surmise! The only very obvious difference in tune is the Thundercat’s leaner A/F mixture, as indicated by the matching mechanical flowmeter readings (AFRA_B) and Innovate wideband readings (LAMAF1). The air conditions on this day were very similar to the day we tested the Sidwinder. One difference was the gasoline—we had 93.0 R+M/2 octane, 7.2% ethanol fuel in the Tcat compared to 91.0 R+M/2 octane 0% ethanol fuel in the Sidewinder (the ethanol has some O2 in it and additional charge cooling effect, both of which should slightly increase HP). But by far the greatest contributor to the Tcat’s higher HP is the reduced fuel flow (note that the leaner mixture on the Sidewinder above 9000 RPM would have been the result of me beginning to pull out of the throttle as revs climbed at the end of the test). Boost pressure was virtually identical on both sleds.

The ECU seems to vary ignition timing and fuel flow depending upon engine coolant temperature. The current Arctic Cat diagnostic computer system doesn’t support the new engine, and we were using the sled’s stock cooling system so we couldn’t really monitor coolant temps during testing (the gauge pod faced away from the control room window). What we did was begin a test at @150f at 250 RPM/second acceleration rate, then do one or two more repeat tests back to back with the ending temp at around 220f. I’m guessing that the “happiest” coolant temp would be in the 180f vicinity where a combo of high CFM (cooler cylinder head, intake manifold and intercooler) / advanced timing would create the best HP—209 to 211 CHP! But even at 200f+ the engine made 206 or more CHP each hot test! On one test (not shown) we began the test with too-cool coolant and the ECU prevented boost from climbing to 10psi and HP was low. Also note in the following graph how precisely the fuel flow matches the airflow from warm to hot—maintaining very constant A/F ratio, closely matching the changing airflow CFM! The Yamaha calibration engineers are spot-on, maintaining constant A/F ratio as airflow changes with engine temp!

=============================================================== Here’s averaged data from two of the 180f-ish coolant temperature tests, where HP was happiest (209 and 211 CHP). EngSpd STPPwr STPTrq BSFA_B FulA_B AFRA_B LamAF1 BoostP Air_1c RPM CHp Clb-ft lb/hph lbs/hr Ratio Ratio psig CFM

6500 160.9 130.0 0.404 61.1 13.16 13.53 8.3 184.9 6600 162.5 129.3 0.406 62.0 13.11 13.40 8.3 187.0 6700 163.7 128.4 0.407 62.7 13.08 13.23 8.3 188.6 6800 165.3 127.6 0.409 63.6 13.01 13.12 8.3 190.2 6900 167.0 127.1 0.414 65.0 12.86 13.07 8.4 192.3 7000 169.2 126.9 0.420 66.8 12.69 13.02 8.6 194.9 7100 172.2 127.4 0.424 68.5 12.58 12.95 8.9 198.4 7200 176.0 128.4 0.423 69.9 12.57 12.87 9.1 202.3 7300 179.6 129.2 0.421 71.0 12.61 12.82 9.3 206.0 7400 183.1 129.9 0.419 72.0 12.69 12.81 9.5 210.3 7500 186.4 130.6 0.417 73.1 12.74 12.81 9.7 214.2 7600 189.6 131.0 0.418 74.4 12.72 12.76 9.8 217.7 7700 192.2 131.1 0.420 75.9 12.64 12.65 9.8 220.7 7800 194.2 130.8 0.427 77.9 12.47 12.55 9.8 223.5 7900 195.8 130.2 0.433 79.6 12.34 12.46 9.8 226.1 8000 197.5 129.6 0.436 80.8 12.29 12.40 9.8 228.5 8100 199.0 129.0 0.439 82.0 12.25 12.39 9.8 231.2

8200 200.8 128.6 0.440 83.0 12.23 12.42 9.8 233.6 8300 202.6 128.2 0.443 84.2 12.24 12.45 9.9 236.9 8400 204.7 128.0 0.442 84.9 12.29 12.48 10.0 240.1 8500 206.8 127.8 0.440 85.4 12.38 12.51 10.0 243.0 8600 208.3 127.2 0.438 85.7 12.46 12.53 10.0 245.5 8700 209.6 126.5 0.438 86.2 12.47 12.53 10.0 247.2 8800 210.1 125.4 0.443 87.4 12.37 12.52 10.0 248.5 8900 209.3 123.5 0.453 88.9 12.22 12.48 10.0 249.7 9000 207.1 120.8 0.464 90.0 12.10 12.38 10.0 250.4 9100 202.9 117.1 0.475 90.4 12.03 12.21 9.9 250.1 9200 199.1 113.6 0.481 89.7 12.08 12.04 9.8 249.3

More data! “EngPwr” is observed (uncorrected) HP. Fuel A is fuel flow from pump to rail, and FuelB is unused fuel returned to the tank. Looks like enough fuel flow to support 300+ HP (uncorrected). And BSAC is pounds of air per HP per hour—in this case a very miserly 5.5lb/hphr= lots of HP available from the tiny turbo in "stock turbo" race form. EngSpd EngPwr EngTrq FuelA FuelB FulPrA AirInT BSAC STPCor RPM Hp lbs-ft lbs/hr lbs/hr psig degF lb/hph Factor

6500 151.3 122.3 174.3 113.2 53.0 67.8 5.31 1.057 6600 152.8 121.6 174.2 112.2 52.9 67.8 5.32 1.057 6700 153.9 120.7 173.8 111.1 52.9 67.8 5.33 1.057 6800 155.3 120.0 173.5 109.9 52.9 67.8 5.33 1.057 6900 156.9 119.4 173.5 108.6 53.0 67.9 5.33 1.057 7000 159.0 119.3 173.5 106.7 53.2 67.9 5.33 1.057 7100 161.8 119.7 173.2 104.7 53.5 67.9 5.33 1.057 7200 165.3 120.6 172.9 102.9 53.7 67.9 5.32 1.057 7300 168.7 121.4 172.6 101.6 53.9 67.9 5.31 1.057 7400 172.0 122.1 172.3 100.2 54.0 67.9 5.31 1.057 7500 175.2 122.7 171.7 98.6 54.2 67.9 5.32 1.057 7600 178.2 123.1 171.4 97.0 54.3 67.9 5.31 1.057 7700 180.6 123.2 171.4 95.5 54.3 67.9 5.31 1.057 7800 182.4 122.8 171.4 93.5 54.2 67.9 5.33 1.057 7900 183.9 122.3 171.1 91.5 54.2 67.9 5.34 1.057 8000 185.4 121.8 171.0 90.1 54.2 67.9 5.36 1.057 8100 186.8 121.1 170.9 88.9 54.2 67.9 5.38 1.057 8200 188.5 120.7 170.8 87.8 54.2 67.9 5.39 1.057 8300 190.2 120.3 170.6 86.4 54.2 67.9 5.42 1.057 8400 192.1 120.1 170.3 85.4 54.3 67.9 5.43 1.057 8500 194.0 119.9 170.1 84.7 54.3 67.9 5.44 1.057 8600 195.5 119.4 170.1 84.4 54.3 67.9 5.46 1.057 8700 196.7 118.7 170.3 84.1 54.4 67.9 5.47 1.057 8800 197.1 117.7 170.8 83.5 54.4 67.9 5.48 1.057 8900 196.3 115.8 171.4 82.5 54.4 67.9 5.53 1.057 9000 194.1 113.3 171.8 81.8 54.4 67.9 5.61 1.057 9100 190.2 109.8 172.0 81.6 54.3 67.9 5.72 1.057

9200 186.5 106.5 172.0 82.4 54.1 68.0 5.81 1.057 Here we compare the basic tuning of the preproduction Yamaha Sidewinder demo sled to our first Arctic Cat Thundercat “bone stocker”. Note the much leaner fuel flow of the Cat—even though it was tested in slightly better air.

=============================================================== The question is, will the final production Cat and Yamaha turbo engines’ A/F ratio be tuned to 12.5/1 (210ish HP) or 11.5/1 (205ish HP)? There’s no need for Sidewinder or Thundercat buyers to wait for more DTR testing—I continually preach the value of having a digital wideband A/F ratio meter on every two or four stroke performance snowmobile, and the new turbo sleds deserve to be monitored! When I constructed this dyno facility 30 years ago, a digital wideband A/F meter (Horiba) cost $4000, and since my credit card was tapped out I couldn’t afford one. We relied, successfully, on the SuperFlow dyno’s mechanical meters. But now, we have multiple Innovate brand wideband A/F ratio meters (one for each cylinder) on the dyno that can now be bought for $150 including O2 sensor, weld-on bung, and digital readout! Not only will this tell you how your new sled is tuned, but it will also tell you, after many miles, if you’ve picked up water/ debris from filling up on the trail! Partially plugged filters can cause fuel pressure to drop—leaning out mixture and causing A/F readings to rise, leaning out dangerously. Remember—excessively lean mixtures can cause damage without detonation that would be picked up by the knock sensors, protecting the engine. If your A/F ratio suddenly leans out to,

say, 16/1 because of low fuel pressure, power will drop some, combustion chamber temps will climb, and if conditions are right, a plug ground strap can begin to turn red without the scouring effects of detonation, and begin to sparkle—igniting the incoming charge well before the proper time--causing combustion chamber pressure to climb to the moon. Preignition is often more damaging than deto, and can be silent to the sled’s knock sensors (and silent to dyno operators listening for knock from the copper tube bolted to the engine). The only indicator of severe preignition is the loss of power, and a two-stroke sled’s headlight “going out”, or a four-stroke sled’s sudden trail of oil smoke from the exhaust and the sweet smell of boiling coolant as it spews from between the block and lifting head, showering the hot manifold and turbo! Spend the $150 and keep an eye on A/F ratio, and for SURE keep an eye on any “retune” ultimately delivered by ECU hackers—trust no one! And if you take delivery of your new Yamaha or Cat turbo sled early this fall, you can examine your stock sled’s tune on the jackstand with your wideband A/F meter. These new widebands have response time nearly as fast as these tiny ball bearing turbos, and a warmup and two or three second WOT whack on the jackstand should tell you what’s happening. The only other variable is, how will the new turbo sleds’ ECU’s be tuned at 0f compared to 70f? Remember, we tried feeding refrigerated air and fuel to the Sidewinder, but the temp sensor seemed too slow to react to the quick 50 degree f drop in intake temp as the dyno’s refrigerated air reaches the engine during dyno acceleration, causing the fuel mixture to lean out. I had that issue with refrigerated intake air while dyno testing SkiDoo Etecs so I bought a stock Etec air temp sensor and ground away some of the plastic coating on it, exposing the metal thermistor, making response time (monitored on BUDS) instant. We have more to learn this fall as these new sleds are delivered to consumers. Thanks again to Tom Ferry for bringing the new Thundercat to DTR. And DTR members—feel free to discuss on the internet forums TCat HP and the info and theories presented here, giving some credit to DTR and the members who support this testing, but please no cutting and pasting of data/ text!

Tom Ferry is obviously pleased with the HP of the new Thundercat.