babbah

I own a 67 435HP Roadster which has a high overlap cam (8 inches vacuum at idle on a good day) and MSD Ignition box (6A). I had been running a Mallory dual point distributor w/o vacuum advance, I am now replacing the point sytle Mallory Dual point distrib. with a MSD Pro Billet Distributor. I currently have a new MSD 8571 Tach Drive Distrib. without vacuum advance.

I have always had running hot problems with this motor.

In preparation for this summer I have just installed a BE Cool aluminum radiator, HD 16" Spal electric fan and original Chevy CC aluminum heads. Have not driven car as yet.

Am I better off replacing the distributor now with vacuum advance or run it with the non vacuum advance distributor? I bought the MSD 8571 (no vacuum advance) 10 years ago and am just now taking it out of the box! The 8572 MSD is the same as the 8571 but has the vacuum advance. Since my cam causes low vacuum at idle, will the vacuum advance be a benefit for me? The vacuum advance model needs 15 inches of vacuum to pull 10 degrees of vacuum assisted advance in per MSD)

Do I shell out another $400 and get the vacuum advance model now? What is the recommendation concerning vacuum advance distrubutor vs. non vacuum (mechanical only) advance?

Will it run cooler with a vacuum advance distributor on street/highway vs. a non vacuum (mechanical only) advance distributor?

What do you recommend?

If vacuum is the way to go, do I connect it to "ported" of "full vacuum" source? Timing specs would be helpful also for either config, non or vacuum distributor.

67L36Driver

Everything but a full on dedicated race car needs a vacume advance, to improve fuel efficiency and reduce engine temp at part throttle.

427/435 original vac can has 0* @ 8" hg and 15* @ 15.5" hg. You might start there.

Vetterodder

I recommend getting the vacuum advance version and, due to your low idle vacuum, replace it's vac can with a B28 (Napa VC1810). The B28 will deploy at 8" so you'll get it's benefit where you need it most. I think you'll find a big improvement in idle quality and, in most cases, lower temps.

JohnZ

Absolutely! You want the vacuum advance distributor, with a can like the VC-1810 that's fully deployed at 8" Hg. (don't know what kind of can MSD uses, but that's the spec you need), and connect it to full manifold vacuum so it's fully-deployed at idle where you need it the most. "Ported" vacuum is an old pre-converter emissions strategy to make A.I.R. work better, and only causes problems.

67L36Driver

If the Echlin VC-1810 proves to be too aggressive (part throttle spark knock) you can try a VC-1765.
Echlin VC-1765 pin starts to move at 6.5" hg and bottoms out at 14" hg.

w1ctc

With my small block running at 12 inches, the 1810 can connected to manifold vacuum reduced average around town temp from 210-215 to 180-190 at 80 degree air temp.