Any motor will always spin up faster compared to another if the rotating mass and therefore inertia is lower.
This is the idea behind lightened forged rods, cranks, pistons and etc in racing engines.
The idea being that the less weight induced inertia in a moving mechanical system the less the pumping losses required to overcome it. This means faster revving and smoother power delivery although by itself it doesnt really give a power increase or increase torque more than the difference in inertial and/or pumping losses (being the amount of the total output required to overcome inherant friction and engine compression).
In the case of an engine 'seizing up' what actually happens is that forever reason increased friction (ie inertia) and pumping losses get to a point where the total output of the engine is less than the energy required to move the piston and therefore the engine will not run. This is the reason why a siezed engine will often respond to a sharp tap on the piston with a drift & hammer and free off because the effective one time power of a clout with a hammer is more than the power of the motor and can exceed the inertial moment.
With any engine, specially ones with power ratings such as these, there is very little difference between motors. It depends more on how the available power is put down as to performance. Have a look on the nacc buzzing archive for the Fantic TI motorcycle - it demonstrates the point perfectly...
Jemma xx
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