Vacuum Test Low?

a cam will affect the vacuum. i have not had a car with a gauge (or that i checked) that had a cam to know if the vac should jump around like that at idle.

on stock fox 5.0's, 15-20" is good. but as said, the cam will knock that down. as i recall, folks with alphabet cams run about 10-12", but i could be wrong.

when you floor the pedal, the vac will drop to almost 0 - that is normal.

good luck with the possible purchase. i hope to pick one up soon (one reason i haunt you guys in here).

My vacuum at idle is around 12-14" and drops to zero even at half- or maybe quarter-throttle. I have a vacuum guage mounted right on my dash because I had severe idle problems when I first put the motor together. As long as it idles I'd say you're fine. And yes, the cam will definitely effect the vacuum.