[Christ]

Well, I can understand that part, but as far as the shape adjustment, I actually meant the shape/size of the flywheel that occupies the inside of the casing... The casing having already been chosen for a specific area to fill inside the car.

So say you have a cylinder already, with a rough dimension of 20" long, 10" diameter (circle). Assuming 2 flywheels, counter-rotational, one would think that 2 8" wide discs would be the best occupation of space, correct?

(That sizing leaves around .7" on the outside edges of the discs, and .7" between them, to account for any "wobbling" caused by bumps/jumps in the car.)

I'm not entirely sure this is something I could actually build at home. I might give it a shot though, even if I can't build a working example, I might at least model it.