Hmmm. Interesting.

415cc limit 2 or 4 stroke.......hmmmmm.

78hp? the 300 will hit this and still be rideable. Andy G rode my 300 at about 75hp and said it was boring...fast but boring....some could read that as very easy and tireless to ride.

A 250 will go this figure but it'd be peaky and you'd really have to keep it on the pipe. Miss a gear and those diesels would be off.

A 415cc stroker, especially a twin would be more than a match for those boilers all through the range. You could always fit tiny carbs to kill the top end mojo to 78 ponies. It'd pull off idle like a buffalo on acid!

Hey Fontyyy. That's not fair to say the two stroke's got an 'unfair' advantage because of the way it works. A boiler, if designed correctly, can copy the two stroke way by sucking in extra juice on the inlet thanks to the scavenge effect of the pipe and inertia during valve overlap, and then clever use of tapers in the pipe can plug the charge in the pipe and ram it back in before the valve closes. On top of this, the stroker's got big holes all around the cylinder to deal with, whereas the boiler's all nice and smooth. So who's cheating now?