[Aussie Mike]

I guess in simple terms the flywheel stores power. The heavier the flywheel the more power it will store. The heavy flywheel takes more power to wind up but gives back more power as it winds down.

A heavy flywheel is good for getting the car off the mark. The inertia stored helps plug the gap between where your clutch engages and the engine starts feeding power through it. It takes a bit of finess to smoothly engage the clutch whilst applying the power to get the car moving The heavier flywheel makes the car a lot more forgiving to get going.

The cars our engines came from were a lot heavier and designed to be driven by regular joe public regardless of skill. Our cobras are a lot lighter and hence easier to get moving. Most of us drive for the pleasure of driving rather than getting from A-B so we hone our skill. A lighter flywheel can be used and the car will still be easy to get of the mark.

For a sporting car that is accelerating and decelerating rapidly a heavy flywheel isn't so good. A lighter flywheel is better because it spins up quicker and slows down quicker too. Great for accelerating out of one turn before braking hard for the next turn.

That's my theory anyway and others may differ. The 7KG flywheel is fine for getting off the mark in my car even with the copper ceramic button clutch.

Cheers