[beatr911]

This is very interesting and I beleive very applicable to motorcycle engines. Motorcycles typically have among the highest power densities of any vehicles on the road. Reducing the power density with atkinson or miller cam timing seems at least at first look a natural fit for improving fuel efficiency. Especially true when the motorcycle is overpowered for the demands of the rider (many of us). Using a small engine at nearly 100% capacity is fun but maybe isn't as efficient relative to BSFC as a slightly larger atkinson cycle.

As for fueling, very long intake valve duration creates real problems with carburetors, and this is why. First fuel is metered to the air that is travelling toward the cylinder, then again travelling back toward the airbox as the piston pushes it back out, then a third time traveling toward the cylinder again on the next intake stroke event. Maybe this could be tuned out with the right carb and jets, but EFI is the real answer. It just has more granularity for adjustment at particular engine speeds and loads and has the possibility of accomidating unusual vacuum pulses from wild cams.

For cam timing specification, it would be really interesting to compare a few "atkinson" cams to a similar engine without the "atkinson" cam. Oh, and also compare the engine dyno plots to look for power characteristics.

The NC700 engine is EFI and low speed, does it use this type of cam timing?

Apparently no one wants my old, very high mile Kawasaki Concours that still runs and rides flawlessly. Being the first to "Atkinsonize" this engine might be the reason it's still around. I don't need 108hp anymore. Derating to say 50hp would be plenty.