I just had my first two test drives using manifold vacuum and the idle in D and the vacuum reading and idle rpm's were smoooth.

The idle was lean at first but once I retuned the carb, the in D idle was excellent.

Note: FBO vacuum advance dist.: 32 degrees in N and in D.

..with a large cam and lo manifold vac at idle, a mopar can will not advance properly and will just dither in and out and give an unstable idle.
..a replacement can that starts advancing at 2 or 3" below the idle vacuum is required.
.. this will give more advance at idle,a cooler more complete
burn,and probably no overheating at the stop lights.
..by running ported vacuum you are probably leaving a little on the table.

Where did the Hemi get its vacuume from? All I have is a port at the back of the manifold. Tim

I was having similar issues with unsteady idle that was surging in D and N. Switching over to manifold vacuum at the suggestion of some guys here took care of that. Idle is now smooth and steady, and no more huge drop in rpm from N to D. I just have a stock replacement dizzy with pertronix though. I would like to learn how to adjust the advance curve with someones help in person though. I've seen it described many times on here but I like to be hands on with someone to guide me when doing stuff like this for the first time.

roe

So a few members have tried manifold vacuum advance.

Found an improvement in idle quality, tip in and mileage and the rest of you insist on telling us it will not work according to instructions from 40 years ago.

At light load, partial throttle. Mild engines will happily motor along at 40-50 deg of timing.

If it takes 9" to pull a typical cannister open. Who cares if the vacuum is fluctuating between 12-22. The can will not move.

I tried running my vaccume advance off of manifold vaccume and it kicked my idle up pretty high and everytime i put it in drive the dash would start vibrating and shaking, but i honestly could not tell a diffference in off idle or light throttle cruising power at all, in fact i made a run on manifold vaccume around my block and on ported vaccume and i swear it was running better on ported vaccume, but yes the manfold vaccume did give it better idle qaulity but other then that i think i will stick to ported vaccume.

Where do you get these cans?

The engine i tried the full manifold vaccume on is a 360 magnum it's putting out 319 horse power at 4750 rpm and 424 ft lbs of torque at 4200 rpm , i'm running hedman headers with 2 inch dual exhaust and an h pipe with 24 inch glass packs along with the edelbrock dual plane rpm air gap intake manifold with a 600 cfm manual choke edelbrock carburetor and the mopar electronic vaccume advance distributer and the mopar electronic ignition. Full manifold vaccume kicked th idle up quite a bit made the dash shake while in drive but still drove the same to me at least with ported vacume i can controll my idle better and my dash does not shake real bad. But i do need to re-curve my distributer, i been trying to decide if i want to take my current distributer apart and shorten the slots so i can run a higher initial or if i should just buy a new mopar electronic vacume advance distributer that has the adjustable mechanical advance in it. The distributer i currently have is about ten years old and i like the idea of being able to adjust my mechanical advance with out having to tear the whole distributer down so im leaning more twords buying a new mopar distributer that has the mallory guts in it so i can adjust the mechanical advance with the distributer in the vehicle.

Hooking to manifold vacuum just masks a problem but is a quick fix for people who lack the now how (like the guy at FBO) to get their idle timing to a place where it needs to be after performance changes.

Vacuum advance was designed to pull extra timing on at highway cruise to give better gas mileage. If your using it improperly at idle you are not making proper use of it cruise.

So going to manifold vacuum at idle you will be giving up some of the performance a motor could offer and will also not be getting all the gas mileage available.

To most on hear the all the power a motor can deliver is not a Goal so my question is why the upgrades???

I can see how its easier to switch hoses around than to design your distributor properly.
Plus it gives you a reason to be in the garage without wrecking anything!

So does FBO recommend manifold vacuum with their distributors?

OK Thanks, just received mine from them and forgot to ask.