Clutches and cast iron flywheels have been known to explode. The higher the torque, horsepower and rpm, the higher the risk. A scatter shield helps contain an explosion much better than a steel bell. An aluminum bell does nothing. A Kevlar blanket over a scatter shield is even more protection. A steel flywheel is much stronger than a cast iron one. Don garlits lost 1/2 his foot to an explosion. Don’t loose yours.