Competition Clutch Ultra Lightweight Steel Flywheels (STU suffix) are recommended for forced induction and/or track and rally racing applications. This flywheel is machined with less material to assist in quicker revving capabilities. Well-suited for Stage 3 and up clutch applications. Made of 4140 forged steel and are a one-piece design. All flywheels are SFI certified. Not all applications have the ST and STU versions available. Flywheel weights vary from 8lbs to 18lbs depending on application. Flywheel: Steel: Ultra Light: 1998-02 Prizm, 03-08 Vibe, 00-05 Celica, 98-08 Corolla, 00-05 MR2 1.8L: 10.00lb Chevrolet: Prizm 98 - 02 1.8 L Engine, Pontiac: Vibe 03 - 08 1.8 L Engine, Toyota: Celica 00 - 05 1.8 L Engine, Toyota: Corolla 98 - 08 1.8 L Engine, Toyota: MR2 Spyder 00 - 05 1.8 L Engine, Toyota: Matrix 03 - 08 1.8 L Engine