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Discussion Starter #1 (Edited)
After fighting over heating problems for a long time I finally thinking about replaced the mechanical advance only distributor with one that also has both vacuum / mechanical advance. I understand the engine temp could drop as much as 20 degrees at least in around town driving with that type of distributor. Now I'm really confused about what of HEI distributor i need. My Nova has a 350 engine, 750 cfm slayer carb. The Comp Magnum cam i have gives me only around 9-12 inch's of vacuum at IDLE. So what vacuum advance unit do i need to run with that low of engine vacuum. Summit has lots of distributors but i don't see and spec. on the vacuum unit on them. I understand their are a lot of different vacuum unit made for different engine vacuum conditions.
 

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Here's a list of the GM vacuum advance canisters and the operating range of each. I would pick one that is all in at the idle vacuum. If you have 9-10"hg vacuum at idle, choose one that is all in at 8"hg.
The HEI cans are listed in the second list starting on page 5.

http://outintheshop.com/faq/Vac Adv Spec.pdf
 

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Mike - 74 Nova Baltimore, MD
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Below is the HEI that I highly recommend. It has GM licensed components (module, centerplate & advance weights, coil), a melonized steel gear, and an adjustable vacuum advance unit... so you can tailor the advance rate for your low vacuum engine.
https://www.summitracing.com/parts/pro-141-682

It's a good idea to purchase an HEI advance curve kit. You will only need the springs from the kit. Do not use the weights & centerplate that come with the curve kit ... they are cheap (keep the centerplate and weights installed that come with the distributor in the above link).
https://www.summitracing.com/parts/pro-66948c/overview/
or...
https://www.summitracing.com/parts/sum-g5212?rrec=true

You will also need to purchase a vacuum advance limiter plate - part #84281. This is also needed and very easy to install.
https://www.summitracing.com/parts/msd-84281

Install 2 of the medium weight springs from the advance kit (this should get your mechanical advance all in by 3000 rpm). Install the MSD vacuum advance limiter plate in the "D" position (this should limit your vacuum advance to about 11°-12°). Set your initial mechanical timing to 15° (vacuum advance disconnected). This initial should give you 36° total mechanical advance. Adjust the vacuum advance canister so that when you connect it to a full time manifold vacuum source, you will see 26°-27° of initial advance (be sure to adjust idle speed before checking your timing).

The above curve works pretty well for most modified engines. You may even notice an improvement in your idle vacuum with the above set-up.
Keep us posted how things work out.
 

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I would go with this adjustable vacuum advance can from Crane.

https://www.summitracing.com/int/parts/crn-99600-1

I have installed a few, and it works well letting you match the vacuum to pull the cannister all in to your engine idle vacuum in gear. Set it up so that the can is pulled in all the way 1.5" lower vacuum than your engine makes in gear. Use a vacuum pump to do it.

The kit also comes with the advance springs you will need.

But, DO NOT install the limited plate the way they say in the instructions! The plate must be installed so that all it does is limit total advance. Not change the starting point. To do this the plate has to be installed on the cannister on the vacuum pot side. PM me your email and I can send you instructions on how to do it.

Or get the MSD stop and use it instead.
 

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Mike Goble is giving good advice, I would add one thing...test the vacuum canister with a hand vacuum pump to ensure it does what it is supposed to. I went through lots of them to find one that was in spec.
 

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Discussion Starter #8
timing

I checked the timing on my Nova. at idle 22* and 34* at about 2500 rpm. No vacuum advance line is plugged off. Also when I built the 350 engine i just installed a Cardone Reman. Factory HIE Dist. from O Railey's. Thinking about getting a Proform 141-682 HIE from Summit setting it up (need to find a shop with Sun Dist Machine) so i will have both vacuum/mechanical advance.
 

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I checked the timing on my Nova. at idle 22* and 34* at about 2500 rpm. No vacuum advance line is plugged off. Also when I built the 350 engine i just installed a Cardone Reman. Factory HIE Dist. from O Railey's. Thinking about getting a Proform 141-682 HIE from Summit setting it up (need to find a shop with Sun Dist Machine) so i will have both vacuum/mechanical advance.
Why not just hook up the vacuum line from your existing HEI to see what it does? You don't need a Sun Machine to get a reasonable advance curve. Yours sounds like it should work, what you want now is a VA can that will get you another 12°, all in at idle vacuum.
 
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