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I think allot of factors come into play and with big bore kits that are adapted to smaller designed motors and they don't live up to expectations

Many times the balance is thrown off maybe because of to small of a crankcase or to short of a stroke.

Proper ignition timing curves is a excellent point on these big bore kits that utilize a factory curve designed for a smaller bore, like Moser stated total ignition advance can be adjusted to equal max hp on 2 engines but a programmable cdi can find horsepower before or after that point by tweaking the curve to the likes of the motor.

But I will also say that a larger bore may have a harder time with residual gases hanging around hurting the combustion process thus killing hp.

Seams also that most extreme cases of cc to hp output are the small GP style motors and they tend to be more square in the stroke to bore ratio and trying to have a square large cc motor kills the rpm potential because of piston speeds.
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