"Daddy, what's molybdenum?"

Good question, because it's been a while since the name came up in my world. It's a hard, silvery-white metallic element used to toughen alloy steels and soften tungsten alloy. The point of it's use in the flywheel of the engine in the Honda Integra Type R DC5 is to enable the construction of a lighter, faster spinning component exhibiting less inertia and enabling the engine to be more instantaneously responsive.

With weight being a key issue in the bhp/tonne alchemy of high performance cars, molybdenum does it's part in reducing the weight of one of the heaviest indivisual components in an engine.

There's more about the K20A Honda engine that powers the car here.