The flywheel is bolted directly to the engine (...the crankshaft in fact...) and always spins at the same speed as the engine. The friction material on the clutch disc makes its contact directly with the face of the flywheel when the clutch is engaged. The disc grips the flywheel, and the power is transferred to the transmission.
With flywheels, weight is the name of the game. Most vehicles come stock with heavy cast iron flywheels that can typically get the job done just fine. However, for racing and high performance applications, flywheels made from billet steel or aluminum have less weight and take far less energy to spin up, meaning that the engine can rev up quicker and get into its powerband faster.
Now, just because an aluminum flywheel is meant for racing applications, it doesn’t mean that it is the best fit for your street car, even if you are running around with a bajillion horsepower under the hood.
“Professor” Will Baty from Centerforce tells us, “Since an aluminum flywheel takes far less inertia energy to spin than an OE iron flywheel, you generally have to slip the clutch more to get the vehicle moving, which results in more clutch heat, and wear and tear.”
There three types of metal that flywheels are generally made of, and the type of metal will determine what kind of application the flywheel is meant for.
Actually, the flywheel is a wear item as well, and will eventually need to be replaced. Baty offered us this guidance on flywheel replacement:
“Most vehicle manufacturers suggest that you change the flywheel with every clutch change. Sometimes if the flywheel isn’t severely heat checked, cracked, or warped you can get away with a minimal regrind. Remember, every time the flywheel is resurfaced, the flywheel is reduced in thickness and mass, which reduces its ability to act as a heat sink. Also, the geometry changes and the whole flywheel and clutch assembly is now further away from the throw out bearing and transmission. In some cases the pivot ball will have to be moved forward to compensate for the removal of flywheel material.”
We’re over halfway through with the Centerforce University courses, but lucky for you there’s no mid-term. Study up though, because next class we will tackle how to pick the right street clutch for your application.