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Discussion Starter · #1 ·
I have done quite a bit of research on the subject and came across the post by the GM engineer covering manifold versus ported vacuum. It has helped me understand the subject much better.

But.......

What I want to clarify is if his expectation to have up to 50* of timing a light throttle from the initial, centrifugal and vacuum advance combined can apply similarly to idle advance.

I ask this because my best vacuum reading at idle is with 38* of timing, vacuum advance disconnected and plugged. And I cannot hear any pinging. So when I set my initial at 18* and reconnect my vacuum advance, I see 38* of timing at idle. Does that make sense?

I have an Edelbrock Performer Plus cam and I have attached pics with the specs and recommended timing and it’s not far off from what I have it set to. I’d like to hear your thoughts on the initial and vacuum advance providing 38* of timing at idle.

I am still buttoning things up on this rebuild before I hit the road so no drive time yet.

Thank you in advance, no pun intended.

Rusty
 

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Sounds in the right ballpark. I'd still want to pull plugs on a regular basis...maybe after a couple hundred miles and then every 500 for a while just to verify there no detonation going on.
 

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Discussion Starter · #3 ·
Sounds in the right ballpark. I'd still want to pull plugs on a regular basis...maybe after a couple hundred miles and then every 500 for a while just to verify there no detonation going on.
Thank you.

I have ordered an adjustable vacuum canister to lower the vacuum advance if needed. The one on my distributor is not adjustable and fixed at 20*.

Rusty
 

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For any combination of parts, it's going to want it's own specific amount of timing. Generally to find the right amount without a Dyno is set the timing for the highest vacuum like you did. You've ended up basically with the right total which is going to tell you what the right initial is for distributor.
 

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Discussion Starter · #5 ·
For any combination of parts, it's going to want it's own specific amount of timing. Generally to find the right amount without a Dyno is set the timing for the highest vacuum like you did. You've ended up basically with the right total which is going to tell you what the right initial is for distributor.
Thank you.

Rusty
 

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R U sure your's isn't adjustable? I found most of them actually are, try putting an allen wrench in the vacuum hole and see if it seats. Unscrewing lowers the total timing as a function of Vacuum. In one case I thought it was fixed but when I reamed the end of the tube where it necked down from being cut to get the next size up allen wrench, to my surprise, it worked to change the vacuum point. I was getting a pop in the flowmasters at high vacuum so backed off till it stopped popping. INterestingly, when I replaced the advance canister, it stopped popping so I ran it full without adjusting. Sure helps the gas milage and makes the car "feel" faster as it has better throttle response when you make small throttle movements. Of course, WOT is always the same as no VA...
 

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Discussion Starter · #7 ·
Thank you for the input.

I have a Pertronix Billet distributor with the Ignitor 2 module. I tried every size of Allen wrench to no avail. I called Pertronix and was told it wasn’t adjustable, so I ordered one that is.

Thank you again.

Rusty
 
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