Dual Idler Noisy Timing Gear Drive SetSmall Block Chevy 3503-BoltMaximum Advance/Retard at Camshaft: 5�Maximum Advance/Retard at Crankshaft: 2.5�Includes Thrust Bearing and Offset BushingsSteelNot for Knock Sensor Procomp Electronics gear drives are great for you folks who want better timing. Their dual-idler design has CNC-machined components and they are easy to install. These drives fit under your stock timing cover and come complete with instructions. Minor machining may be required on some applications.