More distributor talk

[Ricko1966]

A lot of guys get on here and want to buy an A m AZ on distributor. I was looking up distributor specs on a 79 Z28 tonight since I had the info in front of me, I thought I'd post it,to show HEI distributors are not all the same. For 1979. On V8s there were 3 different ones depending on engine size and transmission type. Some years there were many more.Yes the one size fits all works,but not optimal it would be like having one size fits all shoes. @bucket and @PrairieDrifter pointed me at msd streetfires in the past. I did some research they are very tuneable to get the curve and vacuum advance your engine needs. And the factory GM distributors are very tuneable especially if you start with one that's close. And quit buying adjustable vacuum advances and neglecting to buy or make an advance limiter. The can adjusts the required vacuum by putting tension on a spring. So when you get it to eliminate 4* of advance or however many, you did it buy making the vacuum advance can harder to move,which will limit the advance but goes about it the wrong way by changing the required vacuum to move the can fully. Tune your can for your engines vacuum needs and make/buy a limiter to limit degrees.

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[bucket]

These differences in ignition settings are far more important on stock applications of the 70's and 80's with EGR valves, thermal vacuum switches, tall gear ratios, etc. Not so much in a non-stock performance application. Would that be a correct statement?

I've always played the mystery HEI game on my own stuff, lol. It's always run good enough for me. Could correct tuning have increased mpg a tick? I wouldn't doubt it. Could it have improved overall power? Most likely, but not enough for the butt dyno to say so.

I'm basically out of good used HEI's now though. Last time I needed one, I combined parts from 3 or 4 mystery distributors (including a V6 version) to make one good one for my station wagon. It will be the Streetfires from here on out, lol.

 

[Ricko1966]

These differences in ignition settings are far more important on stock applications of the 70's and 80's with EGR valves, thermal vacuum switches, tall gear ratios, etc. Not so much in a non-stock performance application. Would that be a correct statement?

I've always played the mystery HEI game on my own stuff, lol. It's always run good enough for me. Could correct tuning have increased mpg a tick? I wouldn't doubt it. Could it have improved overall power? Most likely, but not enough for the butt dyno to say so.

I'm basically out of good used HEI's now though. Last time I needed one, I combined parts from 3 or 4 mystery distributors (including a V6 version) to make one good one for my station wagon. It will be the Streetfires from here on out, lol.

This is someone I've been dealing with on another thread,kind of like when Rob was dealing with the distributor on his C20. Maybe I'm too serious about ignition,but I think too many people leave too much on the table. I think this car still has another mile or 2 of mpg in it if he resets total for MBT.

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[Matt69olds]

Funny this discussion came up! I was recently researching HEI calibration combinations.

There are probably thousands of different advance weight/cam/spring combinations possible for the HEI. I recently found a partial list on a Pontiac and Chevelle forum. The cams help control the shape of the advance curve, the springs and weights control the speed.

After reading and learning about this stuff, I bet it was a lot of fun to be a Big 3 automotive engineer in the carefree days before all the emissions requirements. Could you imagine getting paid to try different engine calibrations to find what provided the best power and economy?? And if you couldn’t find what you needed, being paid to design it?

Now, the emphasis is tailpipe emissions, with a much lesser concern with the power.

Read this:

https://www.stevesnovasite.com/threads/gm-hei-center-plates-weights-mechanical-advance.199772/

And this:

https://www.chevelles.com/threads/gm-hei-centerplate-degree-timing-values.327577/

And this:

https://forums.maxperformanceinc.com/forums/showthread.php?t=860396