Clutch Query

[John Mc]

So a lightened flywheel would improve engine braking if the revs would drop quicker?

No because it has less inertia.

[CAVEMAN]

In theory yes....you would shed revs quicker, but I doubt in the grand scheme of things you are going to notice much of a difference.

[John Mc]

In theory yes....you would shed revs quicker, but I doubt in the grand scheme of things you are going to notice much of a difference.

I thought Mega was asking about engine braking in terms of slowing the car down?

You would only shed revs quicker under no-load conditions.

If you had the inertia of the car attached to the flywheel through the clutch then the lighter flywheel would take less energy out of the vehicles inertia and wouldn't slow the car down as much as a heavier flywheel... or have I misunderstood physics ?

[CAVEMAN]

I think you are backwards!!

The friction of drive train and road resistance is pretty minimal compared with the engine vacuum caused by shutting off the throttle. This is what causes most of the 'breaking' force.

The lighter flywheel has less mass, thus less rotating momentum so it can't keep the engine rotating. A heavier flywheel, or heavier object in general once up to speed has lots of kinectic energy (remember the KERS systems that died a death in F1?) so the more mass it has, the harder it is to slow down.

So a lighter flywheel will slow down a lot quicker than a heavier one, given the engine vacuum resistance is the same for both.

just google or wiki, engine breaking and see what comes up...sure there is a more technical explanation out there somewhere.