Competition Clutch Lightweight Steel Flywheels (ST suffix) are recommended for naturally aspirated and/or street driven applications. This flywheel preserves low-end torque and driveability. Well-suited for Gravity, Stage 1 and Stage 2 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. Nissan: 350Z 03 - 06 3.5 L Engine