turbo technology

One reason I believe turbo lag is less of an issue on a snowmobile is because of the belt transmission, which quickly reaches top rpm and holds it. A gearbox car has to go up through the gears and constantly varies the rpm, which puts larger demands on the turbo as the exhaust pulses vary.

With 110 hp and 92 ft. pounds of torque at 5,700 rpm, the midrange pull is excellent. Performance was on par with a good 600, which is a world of difference from the early four strokes that were not on par with anything.

Riding this new sled was a delight. The power delivery was turbine-smooth and the machine was very quiet. The turbo powered four stroke mill really impressed in the touring machine application. The broad torque band and the smooth and quiet power delivery gave you a"Cadillac" feeling that led to big grins.

So is 110 hp the limit from Arctic's 650-turbo mill? It is actually just a very conservative start. Pushing some numbers on my calculator, I came up with some possibilities. Since the engine is built with short stroke, four valves per cylinder and double overhead camshafts, upping the revs from 7,250 rpm to 9,000 rpm should be no problem. This change alone could produce 135 hp, smack in the middle of the 700-800cc two strokes. Changing the bore and stroke to 72 x 65 MM would make it 800cc, and still revving at 9,000 rpm could produce 165 hp.

We still haven't fiddled with the boost. Jack the boost up from 21 to 30 psi and you could have over 200 hp under the hood from an 800cc engine revving at 9,000 rpm. Of course, it is not quite as simple as that. New parts would be needed. But, I am using these examples to show the potential of turbo applications in four stroke engines. The turbo four strokes seemed well suited to work with the snowmobile belt drive transmission. A belt drive variable ratio transmission actually seems more forgiving of the turbo and gets the boost up quicker. With the question of turbo lag practically a non-issue, turbos should have a future in the top end of the marketplace, particularly in touring sleds.

Arctic's first effort is impressive, with plenty of room to grow the power. Al Shimpa, Arctic's expert setup man, claimed that an Arctic turbo prototype blew away an F7 one cold evening when the intercooler worked really well. Now let's see how long it takes before the rumor mill starts about the one guy who saw a factory prototype turbo four stroke blow away a 1,000cc Thundercat. Don't laugh, it could well happen.

This story ran in the October 2003 issue of American Snowmobiler magazine