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If you have a look over at "speedtalk.com" in the advanced engine tech section,they're saying that an engine has most power potential when the bore is 1.5 times or even 1.6 times the stroke.Any bigger bore/shorter stroke makes the combustion chamber too much like a thin orange peel.At 1.5,that works out to 78mm bore x 52mm stroke for a 497 cc twin.They'll also tell you that short stroke does not mean less low rpm torque,and other things will affect that.I don't believe that piston speed is a fair way to compare engine stress.Piston speed hardly matters,but maximum piston acceleration matters.If you halve the stroke and double the rpm,you'll end up with twice the acceleration which is too much stress.You could increase the rpm by the square root of 2 and have no problem.78 mm bore and 52mm stroke,with power peak at 9000 rpm sounds pretty safe to me.4 valve heads just allow you to use less cam duration and less lift to make much the same power.Less duration pays off with more torque at low and mid-range rpm.
If you have a look over at "speedtalk.com" in the advanced engine tech section,they're saying that an engine has most power potential when the bore is 1.5 times or even 1.6 times the stroke.Any bigger bore/shorter stroke makes the combustion chamber too much like a thin orange peel.
At 1.5,that works out to 78mm bore x 52mm stroke for a 497 cc twin.
They'll also tell you that short stroke does not mean less low rpm torque,and other things will affect that.
I don't believe that piston speed is a fair way to compare engine stress.Piston speed hardly matters,but maximum piston acceleration matters.If you halve the stroke and double the rpm,you'll end up with twice the acceleration which is too much stress.You could increase the rpm by the square root of 2 and have no problem.
78 mm bore and 52mm stroke,with power peak at 9000 rpm sounds pretty safe to me.
4 valve heads just allow you to use less cam duration and less lift to make much the same power.Less duration pays off with more torque at low and mid-range rpm.
