I have a 6400 mile Pettit ported engine My vacuum at idle is -13 lbs. constant. However when I am decellerating the negative pressure can go to -19 to -21. I have been reading on other posts that it should be -17 to -20 at idle. I checked and double checked the vacuum lines for any loose ones and all is good.
Is this normal?

 

I have a ported motor as well and get a solid 18-20 at 750 rpm's. However, diff. porting by diff. tuners will produce diff. vacuum readings.

 

I have a streetported motor and I'm getting around 13 or 14 in. at 750 rpm. I was wondering myself if I should be getting more vacuum at idle. I have been having some trouble with the sequential turbo operation, so I thought there might be a problem. But, I was not able to find any vacuum leaks at all.

 

I posted some time ago about low vacuum at idle and never got any real response. Mine is about -14 to -15. So, assuming your vacuum is lower, what does that mean?

 

I have 15 at normal idle 750, and no vacuum leaks. Deceleration can be 25-30. I think its normal.