Just wondering if my vacuum reading is normal...
I recently installed a mini-ram on my 350 l98.
I also have a mild cam and afr heads.
When i check the gauge at idle, it bounces between 6 and 9 in/hg.

Is this too low?

 

Yea ide say thats way low. Now that being said it depends on alot of things like how mild that cam really is and where your tapped into to measure the vacuum. To give you an idea of what you should expect a normal factory motor in good condition will run between 20-25 hg. With a "mild" cam ide estimate around 17 or so. So as you can see at 6-9 hg it amazses me it runs. Now as im sure your thinkin right about now is that you have a baseball sized vacuum leak somewhere but this isnt neccessarily the case. There are many things that can effect vaccum reading other than vacuum leaks includeing what i would check first as its the cause of most low vacuum readings and thats ignition timing. Timeing that is too retarded will cause low vacuum. Othing things include stuff like low engin compression ect but start with the timing and chacking over for vacuum leaks with a propane torch. Youll see if you hose down your intake manifold and vacuum lines with propane and you spray it over a leak youll notice the idle change as its sucking in propane instead of just air.

 

Thanks for the insight. I had not thought about the timing affecting vacuum pressures. I have sprayed B12 all over the engine in an attempt to find leaks and have found none as of yet. I have also replaced many vacuum lines and plugged off others to narrow my search.
I think the low vacuum is affecting my brake boost - my brakes hardly work.
I will continue to check for leaks and tweak my timing a little bit.

 

Oh yea with 6-9 hgs your power brakes wont work hardly at all as they brake booster needs engin vacuum to work.