2/20…After comparing the SkiDoo 600 dyno test data between Etec and SDI, we are hunting for the missing 5 HP. While part throttle cruising A/F and BSFC are admirably low, BSFC at peak torque and HP RPM is disappointingly normal. The Etec and SDI single pipes have the same part number. So the lower HP throughout the powercurve is probably either retarded timing, lower compression, lower airflow CFM or some combination of the three.
Since I had no airflowmeter during the Etec test I relied on the Innovate wideband to report A/F. I may try to back into airflow numbers utilizing the wideband A/F ratio and mechanically measured fuel flow lb/hr. If airflow seems to be low compared to carbed and SDI models, it may be the lack of any fuel vaporizing in the engine’s crankcase and transfer ports. Vaporizing fuel absorbs heat, and it’s possible that Etec crankcase temps might be elevated, causing airflow to be lower than carbed and SDI.
Or it may be ignition timing. Jim Cooper’s ETEC software doesn’t yet have timing control like he has with other SkiDoo engines. He is lobbying with SkiDoo to obtain the control of timing on the Etec engine. Otherwise we may resort to an offset ket to add a few degrees overall. But that might mean excessive timing at part throttle (how low can those mid .30’s BSFC go?).
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When Ed Sedlmeier was dyno tuning his SkiDoo SnoX racers last week, he had with him a most dandy battery powered “Pro Vision 618” fiberoptic viewer to look at piston domes. Skinny enough to fit thorough plug openings, it’s perfect for viewing tough-to-see pistons in sleds like SkiDoo and Arctic Cat F twins. I found the best deal on the Pro Vision 618 at www.tooltopia.com $170 free shipping, and ordered one today.