What is a typically 'normal' vacuum reading on a boost gauge, at idle?

 

i could be wrong but from what i know should be around 20

 

20 psi vacuum?

 

I log around 17" of vacuum on my laptop.

 

Hmmmmm.... I thought I had a vacuum leak.... Mine's at around 13" w/ a streetport. Vacuum at idle that is.....

 

Would the vacuum read hire with a vacuum leak?

 

Vacuum will read low with a leak. I run a mild street ported TII motor, and I have 17-18in @ 900RPM idle.

 

if i have a leak wich i suspect but cant find any with propane, would the vacum reading increase with rpm?

 

vacuum at idle will depend on certain things such as compression and is it ported.

My large street port turbo engine with 90psi on all faces pulls in 10inhg. on my stock n/a it pulls 17inhg with 85psi on all faces.
Best way to check for vacuum leak would be doing a leak down test, pressurize the entire intake system and listen for leaks.

 

17-19" of mercury is normal for a stock port motor below 1,000rpm.

 

what about at ~1500-2000?

lower i would think.

 

Stock port motors don't idle above 1,000rpm. Vacuum is greater at 1,500rpm than 1,000.

 

thanx!

 

im new to rotarys but if the rotars are in a certain spot wont the pressure release through the exhaust ports?

and o ya its a stock s5 n/a

 

Hmm...

I guess a more specific question would be... With a bit more than mildly tuned car, during deceleration, is it odd to see such numbers as -500 mm Hg?