Thread: mechanical vs. vacuum advance

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O.K. I ordered my long block today. Now I'm looking at my parts piles and wondering if I should use the Mallory mechanical advance dist. I got off Ebay. It is a comp 9000 unilite distributer, and I have the matching coil set up with the internal balast resister. I remember last year a few of you commenting on vacuum vs. mechanical. How big of a deal is it to use a mechanical distributor?(this is going on a 460 ford engine for street use only)

Generally, vacuum on the street, mechanical on the strip. However, I have run mechanical on the street without overheating or other problems. My '68 GTO with a very radical re-build ran a Unilite, as did my big-block A-bone. I had both worked over with a wizard on a distributor machine, though.

I'm running an HEI on my '34 ford w ZZ-430 clone.

I'd say if you have a mechanical, give it a try. Just make sure you have the right curve built in.

Jack that is what I remember hearing. May over heat. What are some good options for vacuum advance distributors? I can always sell the mechanical advance one!

What do you guys think about this Mallory 85 series HEI distributor with vacuum advance?
http://store.summitracing.com/partde...5&autoview=sku

A vacuum advance dist . will get better mileage and will run better in stop and go driving . the mechanical will get better times on the drag strip . i have tried using the vacuum then unplugging it and making a pass with the vacuum locked out the car is a .05 quicker with out vac -ad .

Would this also hold true for a blown motor?

Distributors with vacuum advance in modern engines commonly used in hot rods always have mechanical advance.


If you have the same mechanical advance curve in a distributor that also has vacuum advance then how does a racing oriented strictly mechanical advance distributor turn better times?


Mechanical advance responds to rpm and vacuum advance responds to load.

Since an engine under full power has a vacuum level very close to zero, the vacum advance is backed all the way off and all the engine gets as far as spark advance goes is what's allowed by the mechanical advance system.