HEI advance curve
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Melting Slicks
Joined: Dec 2009
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From: Thunder Bay
HEI advance curve
Started getting a little part throttle ping last year so I checked out the advance curve on my distributor. (I'm running an MSD Pro-Billet HEI with an MSD-6A box.) I was shocked to find the advance curve wasn't anywhere near where I set it a few years ago. (At my age a few years means anywhere between 3 and 20.) It would appear the springs have gotten weak. When I set it up I set it at 16 deg initial, with 34 deg total all in at 3000 rpm. Vacuum advance was 14 deg. When I checked it today it was still 16 deg of initial but the total was all in around 2500. No wonder I had ping. Anyway I found a set of springs that got me back in the ballpark. So much for preamble. My question is about setting up my vacuum advance. I read on here recently that the vacuum advance should come out at 2 inches below idle vacuum. This is not something I had thought about before so I checked it. What I found was my vacuum advance starts to come in at 5 ins. of vacuum and is all in at 9 ins. My vacuum at idle is 11 ins. I also reduced my vacuum advance to 10 degrees. Does all that sound about right?
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That sounds about right.
Thread Starter
Melting Slicks
Joined: Dec 2009
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From: Thunder Bay
Le Mans Master
Joined: Mar 2004
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From: Little Rock AR
Yes. 11" of idle vacuum and 9" for the canister to be pulled all the way in means it passes the 2" rule. You want it "all in" at idle so the RPMs will be stable.
As for the number of degrees in the can - if is not misfiring at cruise you can run more until it does start to act up, then back off 2 degrees on the can limiter. Then just drive it.
As for the number of degrees in the can - if is not misfiring at cruise you can run more until it does start to act up, then back off 2 degrees on the can limiter. Then just drive it.
Le Mans Master
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From: Hermosa
