HEI distributor mech advance.
Thread Starter
Racer
Joined: Aug 2005
Posts: 456
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From: Forty Fort PA
HEI distributor mech advance.
I did some measuring last night on my HEI distributor (in a BB). Since the distance from post to post (2 inches) corresponds to 90 degrees of crank rotation, the amount of rotation in the mechanical advance mechanism appears to be about 45 degrees (I can turn the rotor half way to the next post when it is ligned up with #1). Does this seem correct? How does this work if I want a maximum of 20 degrees mech advance? I checked the GM distributor on my 350 and it appears to be the same. Is there some stop mechanism I am missing or does the HEI have that much advance?
Tech Contributor
Joined: Aug 1999
Posts: 14,380
Likes: 6,391
From: At my Bar drinking and wrenching in Lafayette Colorado
On an HEI, you can force the weights out with your fingers much farther than what they advance when running. The shape of the weights causes them to stop advancing at a point long before the actual hard stop in the distributor due simply to the weights running out of mechanical advantage. Therefore, you can't measure the advance mechanically - you have to run the distributor on a machine or in your engine and use a dial-back timing light to see how much advance you're really getting and at what rpm it pegs out. The length of the curve is determined by the shape of the weights and the shape of the center post cam. Set your timing up for 36 degrees total and see where the initial ends up. If you don't have enough initial at that point, run the vacuum advance off manifiold vacuum to add an additional 16 degrees of advance.
