Lockout Kit for GM OE HEI Vac. Advance

The Lockout Kit for GM OE HEI Vac. Advance by MSD Ignition (MSD88364) is a precision tuning component designed for engine builders and performance enthusiasts who run aftermarket ignition systems on classic and vintage General Motors vehicles equipped with original HEI distributors. This lockout kit allows you to disable the factory vacuum advance mechanism, giving you full control over ignition timing curves through your standalone ignition controller or tuning system.

The lockout kit functions by mechanically blocking or defeating the vacuum advance port on the GM HEI distributor, preventing atmospheric pressure fluctuations from advancing or retarding your base timing curve. This is critical when running MSD Ignition systems that calculate precise timing maps based on RPM, throttle position, intake air temperature, and fuel octane—vacuum advance would create unwanted timing variations that conflict with your tuning strategy. The compact design measures 6.1 x 1.5 x 8 inches and weighs only 0.16 lbs, making installation straightforward and non-intrusive on your engine bay layout.

Whether you're building a street machine, restomod, or competition engine, eliminating vacuum advance dependency is essential for achieving repeatable, optimized spark timing across all RPM and load conditions. The lockout kit is specifically designed for GM OE HEI distributors, ensuring compatibility with Chevrolet, GMC, Pontiac, Oldsmobile, and Buick vehicles. With its durable construction, this kit is reliable through thousands of ignition cycles and varying engine conditions.