GT500 alternators are prone to failure; high revs are the main culprit. These units were designed to spin at a maximum of 16 to 17000 RPM. Since the vast majority of us have modded these cars and raised the rev limiter beyond the factory setting we often see failures. Our BPS 10% underdrive pulley will keep the alternator revs within a more reasonable range while allowing sufficient charging in the lower RPM band. Save yourself an alternator and minimize the chances of failure with this 15 minute pulley swap!