How much vacuum do you read at idle?
 

I am only reading 12in/hg is this bad?

Definitly if this is stock ports, sounds like a vac leak or really low compression.

My current Vac is 18-20in/hg at 800-850 rpms.. 69k on the motor.


My other motor with a HUGE street port pulls about 16in/hg at 1.1krpm idle with about 3k miles.

It is a stock ported S4 T2.

Just went for a ride and I am reading 22inHG when decelerating. Is this good? I went and sprayed some ether evrywhere and did not find any vac leaks. Motor has 7k on rebuild with used housings. Last comp test was 87psi on front and rear. The builder told me that 90psi is what 13bt's should be?

I have a series 5 turbo with stock ports, im running -.05 bar of vacumm at idle dunno what that is in in/hg

My stock port S5 TII runs between 15-18. Emissions are removed the TB mod performed so it idles anwhere between 1100 and 750 haha. The throttle plates are always opened a bit to hold the idle

I also have all emmissions removed and tb mod. My idle ranges from 700-800.

i run about -5 bar at idle

who has a conversion rate from bar to inHG?

-5bar would be -148inHG no way in hell do you have -5 bar.

750 rpm idle with a streetport and turbo 12-14" of HG.

You don't test for vacuum leaks with flamable spray...gonna be hard to find it. you should test by pressurizing the intake system with the engine off and listen for a hiss.

mine is at 16hg in 800 rpm idle and when i deaccelaret goes up to almost 30hg, i have a street port turbo engine too, i think in your case is normal

it's always going to show a shit ton of vacuum when decelerating but it doesn't matter. What matters is the vacuum at idle. Lots of things can make differant readings including what other people said, vac leaks, intake leaks etc... however the only way to really tell if you have good or bad compression is to take a compression reading. very easy to do using a normal compression gauge. go to rotarresurrection.com and go to the tech section.

I have already done this.

^ Just so you know, 87 psi compression is really low. 85psi is the lowest acceptable compression per FSM. 95-110 is average, with 110-130psi is really healthly.

I am aware of that ,but I have not used a different comp tester to have an accurate comparison. I know that some will give different readings. 87 on this one could be 107 on another. The car runs good, idles good, and I do not have any kind of hot starting issues. who knows?

umm i think you might have forgotten a decimal point there

i pull something like 12 to 16 depending on the rpms lol

Haha... car would move just by suction from the intake.

Intake would colapse in on itself... the universe would be sucked into the rotary..

My rebuilt and streetported S4 TII motor pulls around 12in. at 800 RPM's and about 16in. at 1100 RPM's.

im about 14inHG at 900 rpms, streetport

i forgot to post my car pulls -14inHG cold and -16inHG when warm at 950rpm streetported.

Today after car was completely warm and sitting in traffic it was pulling 14inHG at 700 rpm. This is not a ported motor though.

i read 13-14in/hg on a stockport na @ 750rpm idle.