Is it worth it to skim a flywheel?

[WabTheKing]

Heavier flywheel = more kinetic energy

[Dan]

Some good info but how does a lighter flywheel reduce torque. Surely you would gain torque as you require less torque to rotate the flywheel mass. Or am I missing something, apart from a few brain cells

You don't need torque to rotate the mass as such, only to accelerate its rotation. Conversely, on deceleration, the mass gives back torque that is effectively stored in its rotational inertia.

It's all about inertia. Image an empty supermarket trolly - it takes no effort to push it up to speed, but if it hits something, it'll stop.

Now fill that trolley with bricks. Takes a lot more effort (ie. kinetic energy, torque) to get it moving, but if it hits something (small child recommended) it'll plough straight through it, due the inertia of its moving mass.

A flywheel is the same, but rotational. A lighter flywheel will spin up faster (less opposing inertia), so the engine will rev up quicker. Conversely however, once it's moving, there's less kinetic energy stored in it... so when an opposing decelerative force is encountered, it's got less energy to give back - ergo, less torque assistance.

(I say torque assistance because strictly speaking a flywheel doesn't give you more torque - it can't create torque, conservation of energy dicates that, but it can store a finite amount of energy which is used as torque if the engine encounters increasing resistance - eg. you drop the clutch)

Physics lesson over, it's a tradeoff

[quattrostyle]

I don't know, was thinking out loud, could be I'm missing some braincells, especially after the past few weekends