[Mike_The_Grad]

Thanks MikeB for adding that important note that I forgot to include about #1 TDC being on compression stroke,versus any other stroke in the cycle.

This is exactly why I love this site,people actually care to see others succeed at what ever it is they are facing with these trucks.

Not to hijack this thread, but the reason I was reading it was because I am facing issues with low vacuum at idle, about 15" Hg. On the gauge, some regular flucations of the needle always within about 2" less than the 15" it "floats" around, and always to the lesser side never more than the 15". I recently rebuilt motor starting with .40 over bore(piston's were already .30 over.), new comp cam XE250H,lifters,pushrods,roller-tip rockers,882 reman. heads,new hi-pressure oil pump, H.E.I. had about 4k miles,new module,rotor,autolite AR132 race plugs,fresh rebuilt by me original quadrajet 4mv,new base&steel gaskets,new vacuum lines (PCV line and valve,Vacuum advance line,th350 modulator rubber ends, and brake booster line with check valve and grommet,new vacuum plugs on unused carb ports, manifold gaskets were just replaced last weekend because front and rear leaks because I didn't put enough silicone the first time.) Manifold is original cast iron with exhaust crossover which is worn away and pitted around the crossover groove.
Trying to pin down low vacuum signal. How would I go about finding out how much vacuum the cam I'm using would generate? I was told this was similar to an "R.V." cam, and relatively mild.