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You smart folks out there have helped me before, so I'm asking for more input. I'm rebuilding a 390 for my 67 S-code 4-speed FB, and would like to know if I should go with a v/a distributor, or use the non v/a one that I have (Motorcraft C7AF-12127-E)? I am using an aluminum intake with a C7OF-9510-A 4 bbl Holley, C6AE-J heads, standard bore, C6OZ-6250-B NOS cam (HYD), 3.00:1 rear. I realize that v/a helps on fuel economy at lower rpms, but I've also been told that so-called "performance" engines should not have v/a. I suppose my q here is at what point is an engine considered "performance" enough to go with the non vacuum advance setup? The NOS cam is original equipment for a 390 GT/428 CJ according to my info. Thanks in advance for your advice.
 

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I have never read that vacuum advance harms performance....at WOT, there usually isn't enough vacuum to operate it anyway....I keep it for the fuel economy
 

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From what I know about it most non-vac. advance distributors are for higher reving engines like the Hi-Po where you want the advance to come in later. If it had a vaccumm advance it may come in too soon. I have a Hi-Po distributor on my '66 and it is a little dogged on the bottem end. I spoke to a distributor expert in our club and he said the most important part is the advance curve and what range you want to operate the engine in (low, mid, high.) I decided to keep my Hi-Po distributor, but to recurve it for a lower RPM (I haven't done it yet.)
 

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As long as it is in good operational condition, there's nothing wrong with running a vacuum advance distributor in a performance engine. I did so for many years because that's what I had. I've heard that one can get better fuel mileage with this setup but have not quantified that personally (hard to get good mileage when at WOT *G*)

If you're replacing the distributor with a performance model and the engine/vehicle is mainly going to be used for performance applications, then a centrifugal-only distributor is what I would choose. Simple and effective...

I didn't note noticeable change when migrating from stock distributors to a crank trigger and locked advance in the early 289/302's in the race car but I didn't know that until I experimented...I run a conventional Autotronics billet distributor in the W in there now.

Good luck!
 

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For a car that sees street time, I would run vacuum advance.

If it's a race car that sees only hi-RPM full throttle use, the vacuum advance has no advantage (nor detriment either). For a street car that will see "cruise" conditions, like part throttle and low-mid RPM use, vacuum advance can be a good thing, enhancing economy and part-throttle response.

Like initial timing and centrifugal advance, vacuum advance can/should be "tuned" also.
 

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Centrifugal distributors generally have less advance than a centrifugal/vacuum distributors... On motors with a hi-lift cam, you may not want over 25d advance, so the mechanical distributor would be the better choice (IMO).

A vacuum distributor is better for a stock type motor that can idle at factory timing specs, lower initial timing means easier cranking.
 
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