2004-05 GTO Underdrive Pulley SLP's new 25% underdrive balancer for LS1 GTOs incorporates a number of high-quality features you won't find on any other aftermarket unit. Chief among them are a pair of extra-tall belt-retention walls that eliminate the belt-slippage issues endemic to other LS1 balancers (see photo). Other unique design strengths include 100% steel construction (other brands use steel and aluminum), integral timing marks, and built-in puller-mounting threads. Includes a new balancer bolt and detailed installation instructions. NOTE: Requires 2 new belts (Dayco # 760K6 and # 405K4 or equivalent, not included). For GTOs only. FEATURES * Extra-tall belt-retention "walls"?no more thrown belts! * No aftermarket tensioner required * 100% steel construction * Lighter than the stock balancer * Integral timing marks and puller-mounting threads * Keyed for high-rpm or supercharged applications * Does not cause false knock retard or erratic power-curve dips * Includes a new balancer bolt