Technical Vacuum Advance decision

Should I use ported or full time vacuum to distributor vac. advance? What is the difference/

 

There’s a wealth of information on this subject here if you use the search function.

 

What engine, distributor and carburetor.
Yes volumes of info. Use your search function.

 

Either works a long as you set your initial timing with the vacuum advance disconnected.

 

See which vacuum port gives you the smoothest idle. Other than that they are the same.

 

I remove the vacuum advance all together and screw down the breaker plate to the distributors housing. Then add more initial timing.. Usually end up with 20 to 22 initial timing. I have never tuned an engine that didn't respond well to all this mod...

However if your going to run a vacuum advance use a ported vacuum take off. However most Quadrajet carburetors don't have a ported take off for the distributors vacuum advance. I have had a couple Carter AFBs that had them. These came on Pontiac engines with the Roto hydra matic. Its behind that little br*** screw in plug on the lower left side of the carb. Just unscrew it and put a hose port..
Listen for part throttle pinging, if you have it, try crimping the steel tubing that the hose slides over. This will delay the opening some....

 

As said above, there's a ton of info here and elsewhere on this. But boiled down, the primary difference is ported vacuum tends to run hotter and/or load up if extended idling is done (parades, stop-and-go driving). Every engine combo can react differently, as well as whether you're using a manual or automatic trans. Personally, I'll go with full-time vacuum initially, then switch to ported only if I have idle/off-idle issues. I also prefer a manifold connection over the carb as it can make a difference in timing response.

 

If you have an aggressive cam that gives a rough idle and low vacuum, ported vacuum for vacuum advance may help achieve a smoother idle; a more stock cam may be better with manifold vacuum, try it both ways and see which is better for your engine. This is not a situation with 1 best way for every engine and every application.

 

Thank you all for your responses. The Ford FE turned out to like ported vacuum best. Thank you again.

 

This guy knows what he's talking about!

 

I've always heard the exact opposite! The additional timing at idle will tend to smooth out hot cams driven on the street some, raise the manifold vacuum some, and run a little cooler. This won't work with a stock vacuum canister though.

Most times though people asking the question in the first place don't necessarily understand the finer points of ignition timing, or want to get inside the distributor, or any of that, really. Not a dig at our original poster, but it's 2nd post. "What Oil Should I Use"? is next, I betcha.

The basic errors I've seen is people trying to set up their distributor with the vacuum advance connected, they see 50° BTDC in neutral and think that's "too much".