Should I be seeing normal vacuum readings when I fire a motor for the first time? Or will the readings start to look normal once the rings have seated?
If all is correct, you should see 14 - 18 inches of vacuum at idle. What brand and part number of rings did you use? Was the engine "Bored-out" and honed? Stock or HotRod cam?
[ QUOTE ] If all is correct, you should see 14 - 18 inches of vacuum at idle. [/ QUOTE ] Not to sound like a*****, but that is one of the most ignorant (misinformed, NOT stupid) replies that could've been made. There are a bunch of variables that would determine your particular engine's vacuum characteristics. There is no "correct" number for vacuum! One of the biggest factors is the cam you're running. A big cam will pull less vacuum than a small cam. the size of the ports in the intake, the size of the ports in the head, the exhaust system, and even the Carb will determine how much vacuum your engine will see. You will not get a "true" vacuum reading until the rings are seated, but it SHOULD be close!
what hot rod to hell said thats why power brakes and such dont work with aftermarket cams, LOW VACUUM Walt, gonna need more info on the motor, hope your not trying to diagnose a problem on that new one
i have a really wild cam in my Rocket Olds that i got from skratch,pulls 12 lb.vac. but i'm using a cannister i got from summit,and my p/b works just fine.
Just fired the motor. 331 SBF hyd roller 282/285 222/226 @ .050" .536"/.536" 108 LSA C.R. 10.3:1 Trick Flow TW heads Weiand Stealth intake Carter 625 AFB 1 5/8"******* Supercomps and 2.5" exhaust Eagle crank and rods. Everything was balanced. I'm using KB hyperutectic (did I spell that right?) pistons and JE moly rings. It was a full on rebuild .030" over. Zero decked and everything double checked. The carb and timing arnt dialed in yet (I know that will effect the readings a lot). Vacuum was below 10 and kinda wondering at idle when we fired it. After a quick spin around the block, it was up to 12ish. Just thought it kinda made sense for it not to be pulling as much vacuum until the rings had a chance to seat?
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