What is vacuum advance
- Thread starter bad68coupe
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65ShelbyClone
Founding Member
Look at your distributor. If there is a little canister type thing in the side of it with a vacuum line hooked to it, you have vacuum advance. About 90% of the carbureted street cars out there have it.
65ShelbyClone
Founding Member
i am building a new engine, so i don't know which one to go with. whats the difference between the two? is one better than the other?
Strictly for fuel economy. I don't want to hear anything else, except fuel economy.
The idea is it pulls timing advance as vacuum is increased. Want to see where your engine pulls vacuum? Hook up a vacuum gauge and drive the car. If you're anything like me, you'll be lucky to see much vacuum at all while driving, except when popping it in neutral after a hard 3 gear pull.....
Under wide open throttle you will not see any vacuum, and the distributor will advance based upon the mechanical advance mechanism (Weights and springs inside distributor).
If you're building a cruiser, stock style rebuild, or a car you plan to drive for long distances, go with the vacuum advance. If it's a street/strip car, a car with good hp where you need to know the timing at all times, or a car that is just for show... I like a mechanical advance only distributor. One less vacuum line to worry about.
The idea is it pulls timing advance as vacuum is increased. Want to see where your engine pulls vacuum? Hook up a vacuum gauge and drive the car. If you're anything like me, you'll be lucky to see much vacuum at all while driving, except when popping it in neutral after a hard 3 gear pull.....
Under wide open throttle you will not see any vacuum, and the distributor will advance based upon the mechanical advance mechanism (Weights and springs inside distributor).
If you're building a cruiser, stock style rebuild, or a car you plan to drive for long distances, go with the vacuum advance. If it's a street/strip car, a car with good hp where you need to know the timing at all times, or a car that is just for show... I like a mechanical advance only distributor. One less vacuum line to worry about.
65ShelbyClone
Founding Member
You also have to be sure any replacement carburetors like Holleys have a ported vacuum connection. Mine didn't(Ebay special) and I had to trade the metering block with one of my others that had ported vacuum.
It should.
While ported timing and vacuum advance are mainly for economy and emissions, for street driving I think it is better. It not only takes engine speed as a factor, but engine load as well. It's a better system for a street car.
While ported timing and vacuum advance are mainly for economy and emissions, for street driving I think it is better. It not only takes engine speed as a factor, but engine load as well. It's a better system for a street car.
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