had a quick question what is a good number for the vacuum to read at idle mine sits at 17 to 18. autometer carbon fiber gauge.

 

it's fine as long as it sits anywhere between 18 and 22

 

mine between 16-19 never seen it in the 20s. mitsu rebuilt motor used same block. wondering if its done right

 

The reading will also vary depending on whether you have cams installed.

 

dont think so just bought car doesnt sound like it has cams

 

Here's some vacuum gauge diagnoses tips courtesy of chilton:

• gauge reading steady 17-22 in Hg indicates normal engine in good condition.
• gauge reading low (15-20 in Hg) but steady indicates late ignition or valve timing, low compression, stuck throttle valve, leaking carburetor or manifold gasket.
• gauge reading steady but dropping regularly indicates burnt valve or improper valve clearance.
• gauge reading dropping gradually at idle indicates choked muffler or obstruction in exhaust.
• gauge reading fluctuating between 15 and 20 in Hg at idle indicates stuck valve or ignition miss.
• gauge reading drifting indicates improper carburetor adjustment or minor intake leak at carburetor or manifold.
• gauge reading fluctuating as engine speed increases indicates weak valve springs, worn valve stem guides.
• gauge reading vibrating excessively at idle but steady as engine speeds up indicates worn valve guides.
• gauge reading vibrating excessively at all speeds indicates leaky cylinder head gasket.

 

good info

 

at idle mine is between 14 and 16... if im cruising in 3rd gear and let off the throttle, it'll sit exactly at 20

 

mine also /\

 

i probably have low compression from beatin the f*ck out of it

 

My gauge is reading 39 cm/HG. I did a conversion 39 / 2.54 =15.35. Does this look right to ya'll? I am going to do a boost leak test in a little bit. Any suggestions about what to do after that?

 

mine is @ 50cm/HG during idle so it's looks pretty good.

yours might be a tad low.

 

mines at 14-15 at idle and i have 264/272 cams been like that since the day we put them in

 

Cams and lower compression motors, like ours wont have the same idle vacuum.

The vacuum gauge tests i know are for non turbo cars so you'll have to take all the info with some caution. Of course the turbo is going to effect your readings just be smart about which points look off to you.