AmSnow.com is now SnoWest.com
Twenty years ago, I conceived and built my fully instrumented public dyno testing facility for snowmobile engines. I used a SuperFlow 901 fully computerized auto engine dynamometer mated to a 4,000-lb. capacity hydraulic lift to securely hold a complete snowmobile chassis.
A rubber dampened drive shaft system renders harmless the destructive crankshaft torsional vibrations in connecting this dyno absorber to the engine crankshaft. In 1987, the best stock engines were around 100 horsepower. The most powerful mod race engines I saw then were 130-140 hp. What a difference 20 years makes!
Crankshop's Larry Audette created one of the first 200-hp drag engines tested here around 1990. It was a twin rotary-valved, welded 3-cylinder Rotax and was the most powerful full mod racing engine ever on my dyno. We toasted a big 200 hp that day with cheap $4 fizzywine that we pretended was champagne and sipped from styrofoam cups.
The presentFast forward to 2007 and we've seen 300 hp come and go already. HTG normally aspirated 1200 triples make just over 300 hp, but monstrous 1400-1700 custom triples from Crankshop, Hooper and others can make upward of 350 hp when maxed out on the dyno with perfect carburetion, ignition timing and a set of pipes.
Enter the modern snowmobile turbocharger. Minimal lag ball bearing turbos capable of pumping up to 500 hp worth of air provide the boost required to create unprecedented power in 4- and 2-stroke sled engines. Yamaha's RX-1 and Apex engines can make 400+ hp when tuned to the max with big turbos using race gas.
The newest gonzo engine we have tuned is a Boondocker turbo F1000 2-stroke, with a D&D 1200 big bore top end and stock single pipe. Sled owner Jason Stoviak and tuner/racer Glenn Hall brought the bizarre D&D intercooled Firecat to tweak and tune on my dyno.
One advantage to dyno tuning is to be able to gradually adjust fuel, timing, and in this case, boost pressure to create that maximum, or desired power. Since Glenn would be competing in the "King of the Trail" drag class with this sled, he felt that 400 plus hp was the target for this lightweight Firecat.
In preliminary, but still good tune, we baseline dyno tested the sled with only 10 psi boost. Dyno boost is measured in inches of mercury (2 inches of mercury = 1 psi). Also, fuel flow is measured by the dyno as flow from pump to the rail minus flow from the bypass valve back to tank (Fuel flow A minus B).
After slowly creeping up, gradually adding fuel/boost using Boondocker's controller, Glenn finally achieved his target hp numbers at only 15 psi boost. The added 25% we saw was due to a combination of 23% more airflow SCFM, plus leaner A/F ratio. 414 hp is such an amazing number considering it's more than double the hp of the incredible Crankshop twin rotary valve triple's hp of the early 1990's.
Once Glenn saw 414 hp at a reasonable 15 psi boost, he thought, rightfully, that 450 hp, or more, is within reach. But at 414, the low-revving twin was making 286 ft.-lbs. of torque twisting my 1.25-in. diameter dyno drive shaft, so we opted to stop there.
A happy endingGlenn and Jason left my shop happy, and I quickly got to work creating a new rubber dampened 1.75-in. diameter driveshaft that should accommodate 500 ft.-lbs. and 750 hp easily. I'm now prepared to deal with whatever supercharged, turboed or other monster-powered sleds Glenn and other performance-hungry snowmobilers bring to me for tuning.
Editor's note: Our official dyno tester Rich Daly at Dynoport (www.dynoport.com, 315-253-9631) graciously turned us on to Jim's project. For more technical dyno info on this and other projects Jim is involved in, you can call Dynotech Research, 585-993-2777, or visit them online at www.dynotechresearch.com. More info on products from D&D can be found at www.ddracing.com, and more on Boondocker products at www.boondockers.com.