[olddog]

As far as how quickly an engine can rev, it is physics.

FORCE = MASS * ACCELERATION

Rearranged

ACCELERATION = FORCE / MASS

For rotating systems, FORCE is TORQUE and MASS is INERTIA.

ACCELERATION = TORQUE / INERTIA

So if you can increase the torque by the same percentage you increase the inertia, acceleration is the same.

Reduce inertia or increase torque and acceleration increases.

No where in the physics does it say that longer strokes reduce acceleration. However be careful here. In the inertia calculation, the distance from the center of rotation is a factor. So as you move the center of the mass further from the center of rotation (increase the stroke) the inertia increases, even if the mass remains unchanged. In reality, you need more strength as you increase stroke, and you end up increasing inertia rather sharply, as you increase stroke. However if you can switch to light weight high strength materials, for a price, you can actually reduce inertia.

I expect these mountain motors either make huge power or utilize exotic materials that are a bit pricey. I would salivate if someone has the specs on one.