vacuum or mechanical advance

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Depends on how your using the car. Is it street/strip or a 100% race only?

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You always have mech advance unless you LOCKOUT the dist. , Vac advance is for fuel economy under PART THROTTLE cruising conditions .

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vac advance is for high vac conditions when a little more advance is beneficial

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You always have mech advance unless you LOCKOUT the dist. , Vac advance is for fuel economy under PART THROTTLE cruising conditions .

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100% correct

A motor like that will need a custom curve on the mechanical to match the build. Cam, tire size, stall speed, weight, etc.. all play a part in the desired mechanical advance curve.

Vacuum advance is a feature for economy. Under hard throttle, performance should be unchanged, even on a mild build.

I curve deistributors on my sunn machine, and quite often will delete the vacuum. Usually on applications where the motor is radical enough the the mileage is not affected by not having it. Usually on these same apps, the initial value is so high, that adding vacuum at lower speeds gives it too much advance. Can creat a light throttle surge condition. Vacuum can also be a negative thing on a 4 gear car, as it comes up on the shifts, adding the possibility of theadvance plate sticking with too much advance etc..

Equally, on a milder build there is no reason not to run vacuum advance.

It only becomes a gray area in the middle

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thanks for all the info guy's.I wanted to know which distributor to get and now I know.I bought the car from a car finder, not the builder who raced it in the 80's. The car had a crossover ignition with a computer and the guy did not know how to program it so he put a points dist so I could hear it run before I purchased it.I know its a radical build, i found time slips under the carpet running low 8's.I want to go with electronic ign.

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thanks for all the info guy's.I wanted to know which distributor to get and now I know.I bought the car from a car finder, not the builder who raced it in the 80's. The car had a crossover ignition with a computer and the guy did not know how to program it so he put a points dist so I could hear it run before I purchased it.I know its a radical build, i found time slips under the carpet running low 8's.I want to go with electronic ign.

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Definately no vacuum advance on a car like that.

I doubt many 8 second cars run advance at all. More likely be a lockdown unit with a timing retard to start it.

If it has advance at all, it will be a really short curve.

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