Basically, there's a limit to how much torque can be gotten from any displacement. Beyond that, you have to seek higher rpms for more hp.
Since stroke length is a mechanical limiter of rpms, shorter stroke is the approach of choice. You don't see any high hp bikes with 90mm strokes, much less 104mm strokes. It is done with shorter strokes and larger bores. Larger bore permits larger valve area, whether 2 or 4 valves per cylinder. This gives the breathing potential needed for higher rpms with the shorter stroke.
I don't know the theoretical torque limit for a 500/535 single, but I estimate it is around 40 ft-lbs. It can be attained with a larger bore and shorter stroke, and that will permit the higher rpms to make higher hp.
In the end, tq x rpm/5252 = hp. There is no getting around that. In a displacement category which will always have a tq ceiling, rpms are the way. This is seen in all engine size racing categories. Shortening stroke is the path to more rpms, and bigger bore/valves is the path to breathing at the higher rpms.
The advantages of 4-valves shows more at high rpms. It has the potential to breathe better at an rpm range which exceeds the ability of the 2-valve valve area. And it needs less lift to do it, and it is typically lighter mass. It could possibly improve the power of BW's racing engine at higher rpms, in theory. But in most street engines, that kind of 8000 rpm level is not considered to be reliable for long term with a 90mm stroke. If a high rpm is wanted for longevity, then the stroke should be a length which gives piston speeds in a more mundane range, so that forces are kept under control for reliability over the long term.
Topic: HMC 612cc crank (Read 12726 times)