Simply put, I need more of it. Long story short, carb'd 383 street/strip engne, and was a 5 speed. At operating temp at idle/neutral, engine vacuum was between 9-11 in Hg on my autometer vacuum gauge. AS SOON as I put the built 700R4 and Yank 3600 stall conveter in the car, my engine vacuum(at operating temp in D) is only 5-6 in Hg, and my power brake booster doesn't like it. I have tried adjusting the idle mixture screws for the best idle vacuum that I can get(in gear) and it doesn't really change at all. How can I get more vacuum out of the engine? I already have a vacuum reserve cansiter on the car, but with such low vacuum it isn't helping at all. Don't they make some sort of electric deal that hooks up to you brake booster and creates vacuum for the booster, then shuts off and only runs again unless you need the vacuum? I though I saw something like that on one of those shows on Spike's Powerblock once. They used it on one of the musclecars to save on space. You guys know anything? If so, don't be stingy with the info, I can use anything ya got! Thanks again!

 

It could be the converter that made the difference, how tight was your previous converter?

 

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oops. must not have registered when I skimmed over it. Anyway, going from no converter to even a loose converter will add load to the engine at idle. Did it affect the idle speed? Let's not crutch the problem INSTEAD of properly diagnosing it.

 

I don't plan on crutching anything, however, I do realize the certainty of some things that cannot be changed. My camshaft is a COMP hydraulic roller retrofit(part 12-433-8) that comes in at .520/.540 236/242 110 LSA 106 IC with 1.5 roller rockers. I understand that this is a moderate sized camshaft for a 383, but the difference is load like you said. No load with the 5 speed, and a load with a coverter are 2 different things. The lack of vacuum may be as simple of the design/size of the cam in conjunction with the auto, however, I am trying to maximize the vacuum that I can at this time. I am going to be converting over to a Holley and getting rid of the Edelbrock 750 CFM carb here in a little bit and don't want to spend a whole lot of time especially if it can't be resolved without changing cams. But now to answer your question, yes the idle speed was affected. It went from 750-770 RPM at idle(with the 5 speed) to barely hovering at 500-550 RPM with the auto. I have it set to about 780-800 RPM right now, and if I go any higher then the advance weights in the dizzy start to advance, and my engine diesels when I shut it off. Now, the vacuum reading that I get from my autometer gauge is erratic, and I understand that it is due to the lumpy nature of the cam and I understand that. It acted the same way with the 5 speed, but just reading a higher number.
In my internet searches I came across this chart from COMP about that camshaft. Let's see if it loads....

Dyno Results

Camshaft Part # 12-433-8 Grind # XR288HR-10
Duration @ 0.006": 288° / 294° Duration @ 0.050": 236° / 242°
Max Lift w/ 1.5RR: .520" / .540" Lobe Separation: 110°
Lobe ID#'s: 3316 / 3317 Intake Centerline: 106°
Engine Type: Chevrolet 350 Small Block
Bore: 4.040" Stroke: 3.480"
Displacement: 356ci Compression: 9.25:1
Heads: Dart Sportsman II Intake: Edelbrock Victor Jr.
Carburetor: Holley 750 dbl. pmp. Exhaust: 1 3/4" Headers
Max Torque: 385 ft*lbs @ 3700 RPM Max Power: 406 HP @ 6100 RPM
Manifold Vacuum: 9.5" Hg @ 1000 RPM & 12" Hg @ 1200 RPM w/ no load.


Those numbers that they show on the bottom are close to what I had with the 5 speed. I just don't think that I can get back to those numbers again without changing some parts. It all boils down to the fact that I essentially built a race type engine, and put it in a street car, and now I am having a hard time trying to find a happy medium between driveability and full out power.

 

At this point, that electric air pump thing from your initial post might be the cheapest and easiest crutch, but if it was mine, I'd install a set of Rhoads HR lifters. They'll give you your vacuum back, but by 3500 rpm, you'll be getting the same engine output you're getting now, and you'll keep getting it past 6500 rpm. But you may need to recurve your timing, for a few degrees less advance at the low rpm, but what you have now at medium through high rpm. This is where the electric thinh is advantageous, no re-experimenting with your ignition. But the electric thing takes up space, adds weight, and is obvious.