S&S of Lacrosse, Wisconsin, sells 8500 large V-Twin engines a year—to producers of specialty motorcycles, the aftermarket and private individuals. Indeed, the phrase, “100-inch S&S engine,” has become a mainstay of this market.
In producing so many engines, and in the large displacements demanded by their market, S&S has identified some limits, some weak points, in the basic engineering of these traditionally designed powerplants. Cooling fin area sufficient for 80 cubic inches becomes marginal at larger displacement. BIG thumps from BIG pistons overwork the assembly joints in traditional five-piece roller crankshafts. Those thumps make trouble for clutches and gearboxes—exactly as they have done in “Big-Bang” GP racing engines.
Combustion chamber arrangements that were state-of-the-art when compression ratios hovered around 6-to-1 now require tall piston domes to achieve today's torque-boosting higher compression. Those tall domes are like big “heating fins”—their extra surface area gathers heat from combustion. The hotter your pistons run, the lower the compression ratio it takes to make the engine detonate. There is no win-win compromise here. Push the compression and risk deto, overheating or worse. Drop the compression and lose torque and power.
Makers whose business is engines for highway use know they must somehow jump the hurdle of 2008 emissions standards. Carburetors are doomed. Electronic fuel-injection is the well-trodden path. Is it nobler in the mind to count on muddling through with bought-in solutions and pick-'em-up-at-the-airport consultants? Or should the company meet the problem head-on with its own in-house solutions, which it can in future control and adapt as required?
S&S has made the great leap, designing its own engine around the best available technologies, and at the same time developing a matching electronic fuel-injection and engine-control system. The new “X-Wedge” engine, to be supplied in displacements from 110 to 139 cubic inches, will be based on a new combustion chamber and valve arrangement and a one-piece forged crankshaft with plain main and rod bearings.
Read the full story in Cycle World's January issue, on newsstands now. See it unveiled in Cincy at the V-Twin Expo or in Daytona, in March, at Bike Week. They are also slated for the '08 BigDog Mastiff models. Hang on as we find out more.
