The mechanical advance in an HEI distributor is what determines how quickly timing comes in off idle, and worn weights or tired springs let it drift. This kit supplies new weights, a selection of springs to set the rate of advance, and new bushings, so the curve can be dialed in for the camshaft and compression the engine actually has rather than what it left the factory with.

MSD 8428 Mechanical Advance Weight and Spring Kit Features:

• New advance weights.
• Springs to set the rate of advance.
• New bushings.
• Fits stock style GM HEI and value-line HEI distributors.
• Not intended for billet or Pro-Billet distributors.