Vacuum Advance - Pontiac GTO Forum
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post #1 of 4 (permalink) Old 08-08-2013, 10:14 PM Thread Starter
 
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Vacuum Advance

Again, the question, ported or manifold vacuum for the distributor? I had been convienced that manifold vacuum was the best choice for the vacuum advance for my engine. Many say here that our motors will run cooler and more fuel efficient with the vacuum advance engaged at idle, resulting in about 27 degrees of initial timing when combined with my 15 degrees of base timing. I just bought a new Holley Street Avenger carb for my car and installation instructions say to use ported vacuum. The last Edelbrock carb I bought, same thing, use ported vacuum. Guy at the speed shop where I bought the carb also says, ported vacuum. I called the Holley tech line to ask them about this. They insisted that I follow the instructions and use ported vacuum. I know when manifold vacuum is connected my idle increases to about 1500 rpm's which requires adjustment of the curb idle screw to get the idle down to about 800 where it idles best. Tech told me this changes the position of the throttle plates in relation to the transfer slots and that's not a good thing, not as the carb was designed to function. So for the time being I have the vacuum advance connected to ported vacuum and it runs great. I won't have a chance to test between ported and manifold till this weekend, but was wondering what some of you other guys think about this. I've only got to drive the car just a few miles since the change, I did notice the motor running maybe 3 degrees warmer with the ported vacuum.
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post #2 of 4 (permalink) Old 08-10-2013, 09:59 PM
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I think the whole question is one that's over-thought and over-debated. Run whichever source your engine seems to "like" better and be done with it.

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post #3 of 4 (permalink) Old 08-11-2013, 10:07 AM Thread Starter
 
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My thoughts too. I know with the Edelbrock carb it ran much stronger with the manifold vacuuum, but the motor kind of "lugged" starting, especially when hot. I've got a new powermaster high torque starter ordered, should take care of the problem and also the heat soak issue.
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post #4 of 4 (permalink) Old 08-11-2013, 05:18 PM
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Ported vacuum may indeed work better with your carb set up. But it won't be as fuel efficient and run as cool as a Q-jet hooked up to manifold vacuum. Q-jets on stock intakes are pretty hard to beat for these cars.
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  Pontiac GTO Forum > The 1964-1974 Pontiac Tempest, Lemans & GTO > 1964-1974 Tempest, Lemans & GTO General Discussion

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