Finally, an all-out distributor to replace the OEM LT1 Optispark. Machined from an entire block of aluminum down into a precise housing that fits in place of the factory piece. Then they fill it with a new pickup assembly, a trick timing adjustment mechanism and a new MSD Distributor cap. Once installed, you have the ability to adjust the ignition timing-the only distributor that offers timing adjustability! Advanced optical encoder trigger design for accuracy and reliability Easily adjust the timing ip to +/- 5 degrees Improved housing design and extra bolt eliminates leaks Fresh air vented and sealed to keep the elements out Large ball bearing stabilizes timing through 10,000 rpm's Rotor drive design is positively indexed and cannot slip. Item # MSD 8381 93- Early 94 MSD 83811 Late 94-96