What's acceptable vacuum reading at manifold? I ask because I'm having sluggish brakes after my mods, and I've replaced everything except booster. I believe my chip burner had to make adjustments on my chip for the MAP sensor due to vacuum issues - thus my questioning vacuum.

If I disconnect brake booster vacuum line at manifold, and attach guage, I get 16 at idle - is this enough for the booster?

 

16 is lots.

 

yes 16 is a lot vacuum isn't your problem

 

so, whats a good psi for vaccum?

 

Vacuum isn't measured in psi; it's measured in inches of mercury.

A good number to shoot for is 16". Some stock motors will even produce above 18", but usually those have cams that kill any hope of high HP, because they're optimized for low RPM efficiency at the expense of high RPM flow.

Brakes will usually work fine at least down to 10".

Any time you change anything that affects the idle and part-throttle vacuum, you have to change the chip, for best results. Looking at that vacuum is how the ECM reads the engine's fule requirements; so it throws the fuel (and spark) curve off. Re-programming the chip adjusts what the ECM does at any given vacuum, RPM, temp, etc. point.