V-Twin Harley Engine

How A Harley-Davidson Works

With this and your other post it sounds like you are rebuilding a Harley engine, if so, give year and displacement.

Must be fairly new if fuel injected.

study the design of an old airplane radial engine (especially the crank design and you'll see how the placement of the rods in relation to the crank affect crank momentum, the engine design was borrowed from a radial

I'll throw in two bobs worth re "more power with more cylinders".

The answer is all to do with combustion efficiency and mass/inertia/elasticity effects which impact on engine speed.

As a general rule the bigger combustion chambers are more efficient in the sense that there is less area in relation to the fuel charge for heat to escape, though size probably works against getting a good quick complete burn.

The other major effect is that large pistons and large throw crankshafts get heavier faster than they get stronger, so that small always spins faster - and as you know power is the product of torque x revs.

But all "rules" have their limits and too many pistons mean that friction and heat losses become a problem that overtakes the speed advantage. One relative constant that is relatively independent of piston size/number if the limiting piston ring velocity.

These arguments also go to why over-square engines (where the bore is greater than the stroke) are more powerful than under-square ones.