Thread: vacuum advance?

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hi,
I am currently trying to dial in my 454 and i have a vacuum advance distributer on there. My manifold vacuum is only 5hg so its not even letting the vacuum advance work, so should i just get a lock out kit for it? The only reason im hesistant is because a lot of people talk about how good vacuum advance is.

I also have a problem when i try and restart the truck after it was sitting for only 5 mins, i have to give it a little gas to start, its like its almost running but it just needs a little more gas to get it to.
Is this due to the distributer too?

thanx
david

any suggestions?

The hard starting is not due to the distributor, its probably the result of low vacuum. What are you running for a cam in that engine? A street engine needs more idle vacuum than 5in.

its a 292 dur and 590 exh lift. I dont know the rest of the specs. So your saying that im pretty much screwed unless i replace the cam?

thanx,
david

With 292 duration it should make more vacuum than that. Check for leaks, and reset the valves for starters.
The vacuum advance works at part throttle and gives more fuel economy. If you don't want it, just pull the vacuum line off.

i think its acuall.

thanx for the info.

thanx,
david

like someone said above, the vacuum advance doesn't kick in when you're idling. In fact when timing the motor (initial timing) you should take the vacuum advance off the distributor and plug it.
The vacuum advance gives you a smooth transition between initial timing and full mechanical timing (control by the weights or springs in your distributor). I wouldn't get rid of it, at full throttle it has very little effect on your total timing.

With vacuum advance working properly a BBC should be timed at 8 degrees BTDC @ 800 rpm with 36 total in by 5,000 rpm.

I have run 427, 454 and 502 street engines, all of them cammed up a tad with MSD 6AL and their billet distributor with no vacuum advance. In this case set the initial advance to 12 degrees BTDC and mechanical advance to 36 degrees total by 4500 rpm.

I had a SBC with a 292 cam that was extremely poor on idle vacuum (sat around 5) ...............

Good Luck, Kitz

Big cams idle between 9 and 12" of vacuum depending on duration.

Stock cams idle 18-19" of vacuum.

Looking from here it seems you may be hooking your vacuum gauge to a ported vacuum source.
IE: above the butterflies.

It should be connected to a manifold vacuum source.
IE: below the butterflies.

Be aware that some Holley's have a manifold source up high on the right (passenger in the US) side of the carb.

With your vacuum gauge hooked to ported vacuum and the idle above 650 to 900 rpm you will pull a light vacuum.
The usual for a ported vacuum source is zero vacuum if the engine idles 600-650 rpm.


For a more extensive explanation go here:
http://www.clubhotrod.com/forums/sho...light=Got+Time

thank you guys for the info! When i checked my vacuum it was from manifold and it was idling at around 1150rpms. I also have my vacuum hooked up to the passanger side.

My main question now is, whats the differance bewteen plugging it and acually taking the vacuum advance out?

thanx,
david

No real difference, it just looks cooler without the can hanging off the distributor!