SLP Performance - 04-06 GTO Harmonic Balancer/Underdrive Pulley w/Bolt 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