2017 Arctic Cat Thundercat turbo, tested with Precision EFI stage tuning and Speedwerx turbo mufflers

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Jordan Cannon
6 years ago
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1 2017 Arctic Cat Thundercat turbo, tested with Precision EFI stage tuning and Speedwerx turbo mufflers Billy Howard of Howard's Inc Kubota, SkiDoo and Arctic Cat (and Speedwerx distributor) in Coudersport PA brought this low mile stock 2017 Arctic Cat Thundercat turbo to DTR to test Speedwerx mufflers and the anxiously awaited Precision EFI pump gas ECU reflashes. Speedwerx would like to provide this technology to its distributors, dealers and customers, and are working on a marketing plan with Precision EFI. Sebastien Guay, owner of Precision EFI, spent his early years first doing the Advanced Certification program at EFI University in San Diego, then spent several years in New Zealand working with, and finalizing the development of the VI-Pec standalone EFI system (the preferred standalone used by Hypersports, BMC, D&D, Speedwerx on their X-Games winning supercharged 800 Cat twostroke, and many others). In 2009, Sebastien came back to Canada with fully developed VI-Pecs to market and opened Precision EFI at the Autodrome Saint Eustache racing facility in Quebec, north of Montreal. The facility is set up with a complete fabrication shop, all wheel drive chassis dyno and a fully instrumented engine dyno for building and tuning high end EFI race cars that are run at the Autodrome. They also have a snowmobile chassis fixture for instrumented crankshaft dyno testing like we use at DTR that they use for snowmobile VI-Pec and factory ECU tuning. Today, an important part of Precision EFI's business is marketing/ tuning VI-Pec standalone ECUs in North America and cracking and retuning automotive and powersports ECUs. These three reflashes were developed first on Precision EFI's fully instrumented engine dyno, then field tested last winter in Canada on Thundercat/ Sidewinder beta test trail sleds. Factory detonation protection is surely adequate for normally aspirated operation, but marginal for boosted operation on pump gas, hence the need for extensive field testing prior to release. Precision EFI has reconfigured the digital dash display to include a knock light that will warn the rider of any possible detonation when operating on occasionally inevitable low octane fuel or in abusive, harsh conditions. They also have developed an electronic box to be used by distributors/ dealers for installing these totally encrypted reflashes over the internet on a pay per license arrangement. Billy had with him two Speedwerx stainless quiet mufflers one 2.25" ID and the other a higher flowing and just slightly louder but easily trailable 2.5" ID. We tested the fuel in the tank with our Zeltex 101C octane/ ethanol % tester, and it was 92.2 R+M/2 octane with 3.3% ethanol. At the beginning of the test session, the air was hot and humid. The Thundercat EFI will adjust fuel flow to compensate for changes in temperature and barometric pressure, but can't measure humidity with its speed density system. So the water in the air displaces O2 with no change in fuel flow, resulting in slightly richer mixture and reduced HP. Note that the stock fuel curve leans out mixture as revs climb beyond peak HP RPM. Based up on their own winter air dyno testing, Sebastien had expected HP to be closer to 280, and plans to return after optimal cold weather has arrived in WNY. The DTR refrigerated

2 intake air system can provide 1000 cubic feet of dry winter air in August, but our experience using that system on our first preproduction Sidewinder showed the stock intake air thermocouple is too slow to react to the sudden 60F drop in intake air temperature during the 10 second transient dyno test causing leaner-than normal A/F ratio. We had the same experience with the plastic coated SkiDoo Etec intake air temperature sensors, and now use one with plastic carefully removed exposing the metal element when testing with winter air in summertime. With that, the BUDS shows intake air temperature drops as quickly as our rapid response custom SuperFlow intake air temp sensor. Stock baseline in 75.8% humidity,.75 in hg vapor pressure air EngSpd STPPwr STPTrq BSFA_B FulA_B LamAF1 ElpsTm BoostP FulPrA RPM CHp Clb-ft lb/hph lbs/hr Ratio Secnds psig psig Leaving the stock ECU in place, we installed the Speedwerx 2.25" muffler. The reduced backpressure allowed a bit more boost pressure that the ECU compensated for-- delivering additional fuel flow. Also, note the Elapsed Time of the first two tests which is virtually identical--critical in ensuring perfect repeatability during transient testing with

3 any dyno. The SuperFlow 902 water brake absorber with new style PID controller gives us this identical rate of engine/ absorber rotor acceleration. Stock ECU, Speedwerx 2.25 quiet muffler EngSpd STPPwr STPTrq BSFA_B FulA_B LamAF1 ElpsTm BoostP FulPrA RPM CHp Clb-ft lb/hph lbs/hr Ratio Secnds psig psig Reinstalling the stock muffler, Sebastien installed a "Stage 1" reflashed ECU. This gave us an extra 1.5 psi of boost, and a nearly 20hp increase over stock with even safer A/F ratio than stock. Precision EFI stage I tune, stock muffler EngSpd STPPwr STPTrq BSFA_B FulA_B LamAF1 LM1Air BoostP FulPrA RPM CHp Clb-ft lb/hph lbs/hr Ratio SCFM psig psig

4 Next, a larger but still quiet 2.5" ID Speedwerx stainless muffler was installed with an ECU with Precision EFI Stage II tune. This brought boost up to 14psi, and with still safer-than-stock A/F ratio generated well over 250hp. Note that the Precision tuning eliminates the gradual leaning of mixture as revs climb toward the rev limit something critical when running "out of gear" on the lake and having revs climb toward the rev limiter. Remember the factory deto protection may be adequate at stock HP levels but may lack the extreme, rapid reaction (fuel enrichening and timing retard) necessary to protect the engine properly from detonation at 250+ HP. Precision EFI Stage 2 tune, Speedwerx 2.5 quiet muffler EngSpd STPPwr STPTrq BSFA_B FulA_B LamAF1 LM1Air BoostP FulPrA RPM CHp Clb-ft lb/hph lbs/hr Ratio SCFM psig psig

5 Finally, here's the 2.5" Speedwerx muffler with Precision EFI's "Stage III" tune. This adds another two psi of boost and nearly 70hp more than stock on 92.2 octane pump gas! Note the conservative A/F ratio all the way to the rev limiter. And also note the gradual application of boost as revs climb from lower RPM. This boost curve is designed for maximum midrange acceleration at WOT without risking encountering deto that might occur from creating excessive torque (high operating combustion pressure) at low RPM. Remember--detonation is a time-dependant phenomenon so it's wise to keep WOT tuning moderate at low revs, and increase the boost as revs climb. The time-dependant issue explains why we might be able to safely make more HP on pump gas with the high revving, smaller bore triple. Most wise tuners always felt the 250 was the pump gas limit on the Suzuki turbo bigger bore low revving two cylinder (many who have tried to operate the boosted Suzuki twin on pump gas at higher HP levels had to resort in installing heavy head studs to keep quietly detonating engines from lifting the heads and spewing coolant). But the lower torque, higher revving Yamaha triple with less timing advance surely explains its greater pump gas HP output with no signs of detonation. Precision EFI Stage 3 tune, Speedwerx 2.5 quiet muffler EngSpd STPPwr STPTrq BSFA_B FulA_B LamAF1 LM1Air BoostP FulPrA RPM CHp Clb-ft lb/hph lbs/hr Ratio SCFM psig psig

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Sebastien and Stephan from Precision EFI. Note the copper tube bolted to the head that would send unmistakable clicks of detonation into the control room. No clicks were heard. Speedwerx 2.

8 Sebastien and Stephan from Precision EFI. Note the copper tube bolted to the head that would send unmistakable clicks of detonation into the control room. No clicks were heard. Speedwerx 2.5 stainless muffler in stealth mode with factory heat shield in place. Also note the wide band O2 sensor in the stainless tubing of the turbine outlet pipe. This is Billy Howard s asphalt sled with Stage III reflash getting ready for the AmSnow Shootout.

2011 American Snowmobiler/ DTR Adirondack Shootout sleds

2011 American Snowmobiler/ DTR Adirondack Shootout sleds This year, our Shootout media partner American Snowmobiler suggested two classes 120 HP and 150 HP. The 120 class would comprise of the Etec 600,