Adjustable vacuum advance unit for GM HEI distributors, designed to fine-tune ignition timing for improved drivability and performance. Suitable for GM HEI models up to 1996 as well as Ford, AMC, and Chrysler distributors built in the HEI style.

• Provides 13° of total vacuum advance
• Adjustable design allows precise tuning for optimum performance
• Fits GM HEI distributors through 1996 (non-computer controlled)
• Also fits Ford, AMC, and Chrysler HEI-style distributors
• Not compatible with computer-controlled HEI units
• Sold individually

Setting Instructions: Rotate the adjustment screw counter-clockwise to reduce vacuum advance. Do not exceed 5 full turns to avoid screw disengagement.