Question after six pack rebuild - vacuum advance?

[am3rican]

I sent my six pack setup out to get rebuilt. They came back looking fantastic and were tuned and dynoed before they were shipped back.

The shop who did the rebuild and dyno recommended I don't run a vacuum hose from the carbs to the distributor. They even indicated they were tuned without the vacuum advance.

Do any of you run without the advance? I don't want anymore headaches and want to get her running this spring.

My car was meant for the street and not the track: 1968 Plymouth roadrunner with a 69 440 six pack setup and Mild cam.

 

[GetX'd]

I've never had mine professionally done - I may someday. I'm sure it would do some real good. I run mine w/o the vacuum advance because that was the instructions on the electronic ignition from MSD. I used to run it with my old mallory dual point - but it's been so many years that I honestly don't remember too well. Just know I don't now and the car runs fine.

If you don't mind me asking - how much and who did your carbs?

 

[493 Mike]

Using the vacuum advance will increase your MPG. Look up the Mopar Action articles by Rick E. He is a rabid vacuum advance advocate!
Mike

 

[AR67GTX]

I don't under stand their statement about the carbs being set up w/o vacuum advance. OK - so they were run on a dyno and tuned - do they really expect you're going to be able to put them on your engine and run them without checking and tuning the idle circuit??? Was their test mule identical to your engine. What was the elevation of their facility compared to where you live? From your description of intended use I think you should run vacuum advance. It should be full time vacuum advance from a manifold point or carb port sourcing from below the throttle blades. It helps your engine run cooler, improves gas mileage (if that's important) and improves idle characteristics. My 2 cents.

 

[lewtot184]

tuned to not run a vacuum advance? ridiculous! how can you "dyno tune" a carb(s) on a different engine than what they were intended to run on? clowns!

 

[dadeo]

Just to throw it out there, my six pack motor does NOT use the vacuum advance and I'm running the original Prestolite dual point distributor but I did recurve the distributor using centrifugal advance so to me you could go either way.

 

[Superb Bee]

I have had carbs dyno tuned and shipped back to me bolted them on and didn't have to touch a thing, just my 2 cents, maybe be worth less than that to some, lol.

I have also taken a 6 pack off of an engine that ran good, then put it on a different engine 2 years later and it ran good, lol.. NOW could a dyno tuning get me a few extra hp points? probably could have, but it idled well, no hesitation and made power with out me having to pay for dyno time, lol.. I was happy..

 

[rarefish]

The old vacuum advance mystery. Why factory distributors and some aftermarket have them and the "race" high performance distributors did not have them. On the street, they have an advantage of giving better gas mileage under a high vacuum, steady cruising speed condition. At the strip, they are pretty much totally useless. When the light turns green and the throttle goes wide open, there is very little manifold vacuum. You are not building high manifold vacuum running down the 1/4 mile. The vacuum advance never comes in to play. That is why "race" distributors don't have them. A lot of people believed the myth that disconnecting the vacuum hose would somehow increased the performance of their engine.

 

[PurpleBeeper]

I've had my six pack setup for about 30 yrs. and I do not use the vacuum advance. FYI, I've got a street car with a mild cam, Mopar electronic and MSD 6A ignition box. While tuning my car, what I found is that after adding a cam (even my mild one), I did not get very much vacuum at idle/cruise as stock. I'm getting 12"Hg at idle. I tried to run the vacuum advance, but (I'm guessing) the motor didn't have enough vacuum to make the vacuum advance "operate as designed". After trying to tune the motor with & without vacuum advance, I settled on leaving it un-hooked. It seems to be running fine since in 2nd & 3rd gear you can hear the tires trying to break loose, so it seems fine without it.

 

[rarefish]

The vacuum advance is hooked up to the "ported vacuum tap" This is not manifold vacuum which is below the throttle plate. Ported vacuum is above the throttle plate. The vacuum advance should not come in at idle engine speed anyway. It gives you more advance at cruising speeds. On my street driven cars using the MP electronic distributor. I'm running about 15-16 degs at idle, 35-37 deg with the mechanical advance fully in. 50-52 degs total advance with the vacuum line hooked up. The only problem is the MP distributor mechanically is fully in at about 1800 RPM. For the street I rather have that in at about 2300-2400 RPM.