EXEDY ZF503 Chromoly Racing Flywheel The flywheels are made from solid one piece billet chromoly steel or chromoly steel forgings Exedy steel billet and forged steel flywheels have passed engineering tests to 15000-18000 rpm The ring gear and teeth are integrated onto the flywheel unlike an aluminum flywheel where the ring gear is pressed onto the flywhell and has the possibility of seperating from the flywheel due to the different expansion coefficients of aluminum versus st They are specifically designed to reduce weight and inertia for better engine response Most incorporate special design features to enhance airflow which improves the cooling of the clutch