Flywheel is vital on a piston engine, since it can preserve momentum from one combustion stroke to the next. In early times, engine was not efficient enough, so there has to be gigantic flywheel to keep engine running. Vehicles are currently benefited from heavy flywheels. However in terms of racing, less weight is better.
But if engines in modern times do not need those big heavy flywheels any more, why don’t vehicles come from factories with lightweight flywheels?
In fact, heavier flywheel has its unique advantages. Stop-and-go driving, silky engagement and reduced harshness are all essential for pleasant driving experience. Recently some vehicles come with dual mass flywheels, which are double-piece design with a spring-hub center, similar with clutch disc. This kind of design highly decreases noise, vibration and harshness, which is critical for modern street vehicles.
With respect to racing, winning turns out to be pleasant driving experience and weight becomes the obstacle. In a racing vehicle, noise and vibration from lightweight flywheel is worthy, but how much weight can be reduced?
Lightweight flywheel is approximately 40-60% lighter than OEM, but the figure varies depending upon specific model and whether OEM is single mass or dual mass.
With lightweight flywheel, driver can find the engine revs more quickly. Driver can release horsepower the engine has made and send it to rear wheels, instead of having it dissipate as parasitic losses. Of course, these exist other advantages as well.
It is useful and helpful to reduce clutch wear and improve clutch efficiency. With lightweight flywheel made of aluminum, which has better heat dissipation, the clutch can have a longer life. Compared with one solid steel surface, which can keep heat in clutch area, overheat it and create more wear, the material can dissipate heat through two surfaces. With less rotational mass, it is beneficial for faster and smoother shifting as well, and it is easier to get in and out of the gates and do rev-matching for shifting process.