vac advance or no vac advance

[galaxastang]

Hey guys, still getting all the parts together to wake the rebuilt 390 in my Gal. I've been looking at the new Pertronix flame thrower dis. with the ignition III module. Doesn't need a ign box, easy to adjust mechanical advance and has a digital rev limiter, I need your thought getting it with or without vac advance. Mostly street with some strip time, Comp cam 282S, CJ heads, edelbrock streetmaster and 750 holley. With it being mostly a street car, I was thinking with vac advance. THANKS

[jayb]

I think you could go either way.  How big of a concern is mileage?  If you don't care too much about mileage, I'd go with a straight mechanical advance just for simplicity's sake.  If you do care, then that combination ought to work fine with vacuum advance.  Toss up...

[galaxastang]

Weekend warrior car, with a run to the shore here and there(about 60 miles). Not to concerned, how bad do you think will it effect gas mileage? Thanks

[jayb]

I think gas mileage would primarily be affected on highway driving, when you can use another 15-20 degrees of advance.  You might pick up a couple MPG with the vacuum distributor.  Hard to say for sure...

[galaxastang]

What if any problems would I be running into if I ran the vac advance plugged and just used to for cruises to the shore? I seem to remember doing that with a 74 F100 390 I had many moons ago, not sure it would make sense doing that now. 

[machoneman]

Street car = vacuum; race only = no vacuum.

A vacuum advance even on a racer though has zero impact when running at any type of  track. Why give up mileage then?   

[Joe M]

From what I've heard, vacuum advance will help with cooling and will make the car idle cleaner.

[galaxastang]

Vac. advance it is and your right, it won't hurt it at the track. It is more of a street car and giving up any kind of gas mileage would be silly. Thanks guys!

[galaxastang]

Another good point and reason why I'm ordering it with vac advance. Thanks

[mlcraven]

HUGE addition to eventual re-sale 

[fe66comet]

Main issue with vacuum advance is unless you are running everything stock  it will play havoc on your timing. If I change cams or carb, intake I go mechanical to save a lot of runaround to end up changing the distributor anyhow.

[ScotiaFE]

I can't agree with that.
I've run both MSD and Duraspark on the same healthy 428 and never seen any real
or imagined difference in performance.
A bit better milage with the vacuum can on the fast highways.

Edit: There is some debate about ported and unported vacuum. I always use ported vaccum.
        That's the port above the throttle plates on the carb.

Main issue with vacuum advance is unless you are running everything stock  it will play havoc on your timing. If I change cams or carb, intake I go mechanical to save a lot of runaround to end up changing the distributor anyhow.

[fe66comet]

I have always just set my timing to do its thing based on torque curve, always worked well for me. Also on any performance engine I build vacuum at low rpm or idle usually causes havoc. A cam with a larger lift say around 500 becomes an issue, at least from my experience.

[66FAIRLANE]

Well...if people are gunna start posting pictures of Fairlanes doing burnouts.......

[jayb]

I don't see any Fairlane, just a bunch of smoke   Maybe we need a gratuitous burnout thread on this board...