i heard different comments from 18 - 22 hg in to 20 - 22 hg in.

i don't know if mine is normal, sometimes it's 18-19 hg/in then sometimes it's 20hg in. if it was in 18 hg in(when a/c on, it will jump up to 16 hg in once the a/c compressor turns on. is that normal? or is there trouble?

 

A little low, but normal.

21 is ideal IMO, but anything from 18-22 is acceptable. Really, you need a good vacuum gauge to tell an accurate difference from 18-22. If you are using an Autometer boost gauge, forget it.

The vacum changes becuase the idle is bumped up with the AC on. It should drop a bit and yours does. So all is well my friend.

Randy

 

 

Mine usually sits about 18-20 most times. sometimes it drops down to 16-18 other times it's up at 20-21....autometer enough said..

 

mine sits anywhere from 19-20. also depends on your vac. lines and how the unit is installed.

 

yup, i'm using autometer boost gauge. well, i guess i'm on the safe side. thanks guys.

 

The cam gear setting and cams will have a lot to do with your manifold vacume. On a fresh motor , stock cams , at zero you should see 22-23 " HG at normal temperature. but 18 -22 is ok( With stock cams).

 

yeah, i see about 22-23.

 

i get 16-20in depending. I have 8.8:1 compression so would that make a difference or no.

 

compression wont change the vacuum. it depends on how tight the motor was built. also, if the car is rich at idle you will see lower vacuum readings. when we first started my car after building the motor i had 1 inch of vacuum and thought i was screwed. Turns out my map sensor was bad. after that it pulled 20 inches strong.