Ditto with Centerline. I ran my close to stock sbc on a ported vacuum source for a long time, but I never could figure out why the car was such a slug off idle, it had very little low end power, my combo consists of a crane 210 216 duration cam, flat top pistons, 041 heads, weaind stealth intake, demon carb, headers, HEI with flame thrower coil and module, 3.23 gears and posi.
The car wouldn`t get out of it`s own way off idle, it was the most pathetic unthrottle responsive slug I ever owned, I didn`t understand why with the pieces I chose it had no power, I had read many posts that said vacuum advance was needed at idle and should be on a manifold source, I didn`t believe it, since I didn`t see the need for it at idle, BOBCRMAN suggested I move it to a manifold source, I did and the difference was incredible, off idle it moves and moves fast, throttle response got a 100% better, mileage improved greatly, It finally ran like it should have ran. The need for vacuum advance at idle and off idle is because these mixtures are lean, and lean mixtures burn slower than do rich mixtures, so the added advance is needed. Vacuum advance is especially effective in a low compression application.