Tech Notes: Return of four-cylinder sled?

Breaking out of the 'fashion box'
Today’s snowmobile designs are locked in a box that was created by fashion rather than sound, basic engineering. The first step came when the Karpik brothers created their Blade sled. They turned the engine around so the carbs pointed forward and the pipes came out the rear. With no pipes in the front they could style their sled with a skinny nose which gave it a distinct appearance.

■ Styling gets top priority

The corporate copy-cats quickly jumped on the idea, and almost all the manufacturers demanded that their sleds have skinny noses as a styling trend. The second nail in the “fashion box” was A-arm ski suspension. A-arm suspensions had an advantage in Snocross racing and therefore they became the new hot trend. With skinny noses and A-arm suspensions, you run into a space problem, which means you can only fit a twin engine in the allowable space. As a result, the manufacturers declared that triple engines were dead; they were now only going to build big twins.

The trouble with big twins is that they have limitations with their own internal stresses when strokes get longer and bores get bigger. This not only affects cranks and pistons, but the stronger power pulses have a jackhammer effect, rather than a smooth torque delivery, and this is hard on clutches and belts. All this puts an upward limit on performance. Today’s 850 motors are hitting slightly under 170 HP, and the upward limit even with 900cc is probably 180 HP. In the meantime, Yamaha’s SRX turbo 4-stroke is over 200 HP, and at the “East Coast Battle” this year, they easily put 10 MPH on top end on the 850 2-stroke sleds.

Although the two-stroke manufacturers declared that triples are dead, they may have to do a rethink if they want to reclaim “King of The Lake” honors. How important is a “King of The Lake” reputation? A lot of attention has been focused on Snocross, off-trail crossover, mountain sleds and snow bikes lately, but the fact is that this highly specialized group probably only account for 30 percent of the snowmobiling market place, the other 70 percent ride groomed trails, lakes and rivers. This group doesn’t necessarily want an extra long travel suspension, high riding positions that rolls too much in corners and skinny styling with too small windshields. This is one of the reasons many hold on to their Yamaha SRX, Arctic Thunder Cats, and Ski-Doo Mach Z triple sleds.

If you want to get more and still reliable power, you need more cylinders, shorter strokes and smaller bores. In addition to more power, you also get smoother power delivery that is easier on clutches and belts with three and four-cylinder engines.
Pro drag racing champion Jerry Solem checks out the compact installation of the V-4 1000cc Drag Racing Engine.
Some would argue that more cylinders mean more weight, but if you are up against Yamaha’s 4-stroke turbo you should still end up lighter with a 2-stroke triple 1000cc or even 1200cc. Four-cylinder engines are nothing new; Arctic’s King Cat still competes on the Vintage Oval circuit. Yamaha’s V-Max 4 was a hugely popular sled in spite of its inline design and wide body. I never heard anyone complain about V-Max 4 styling. The biggest problem with the V-Max 4 was its long crankshaft which acted as a gyroscopic stabilizing force in a straight line, but made it harder to handle in tight turns. This made it hugely popular for straight-line drag racing and speed runs, where highly modified 1000cc V-Max 4 race sleds produced close to 300 HP.

■ Less with more
There is another alternative to an inline four that solves both the weight and width problem, and that is a V-4. A V-4 based on outboard technology need only be two inches wider than a twin as the rods sit on the same pin separated by a divider plate with sealing rings. A 90-degree V-4 ends up being lighter than a triple by 30 pounds.

We built such an engine in the early ‘90s and it was a light, compact package with a very smooth power delivery that was easy on clutches and belts. With the short crank and low gyroscopic forces, it was also quick handling in the turns. We raced them in drag sleds as 800cc and 1000cc motors. After a usual development period, the engine ran reliable in both the sleds. In the drag sleds it ran 12 seasons without a problem.

In old-school engineering, we selected the power source that we wanted, then the chassis and suspension were designed around it. As a last step, the stylist came in and wrapped it in a nice package. Styling was never the first consideration back then, so form followed function. That was exactlyπ what Bobby Unser did over 45 years ago when he designed the first IFS suspension that would allow a large “race-winning” engine with plenty of room for triple pipes.

Personally, I don’t feel “skinny noses” have made the sleds look any better, but they have made sleds harder to work on and colder to ride. If a stylist knows what he is doing, he can make anything look good, warm and accessible. Making style first priority is bad engineering.

If a 90-degree V-4 engine would ever get approval in a snowmobile boardroom, we might see a 1200cc version making 250 HP at 8000 RPM. In a light and responsive sled, with appropriate styling and suspension tailor-made for lakes and trails, this would be the ultimate “King of The Lake.” Game over!
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