Just curious what everyones Vac typically reads at idle. I know it is supposed to be around 20Hg of Vac but I have only seen that when its cold.
I often see 17-18 and today was reading as low as 15-16. Is that unusual or indicative of an intake leak? What is considered too low?
Thanks in advance.

 

mine is at 19-20. Never goes below that.

 

Same.

 

Idle with cams was discussed in this thread if this helps
https://my350z.com/forum/forced-induction/139274-guys-with-cams-and-tt-manifold-vacuum.html

 

Mine is at -20 hg/in 95% of the time but sometimes wavers between -18 and -20

When driving and coming to a stop I can see it dip to -24 sometimes..

When I was playing around with BOV spring rates my idle vacuum seemed to fluctuate depending on what spring I used.. when I used a lighter spring, it idled at -18 to -16

When I used a heavier spring, it idled at -22 to -20..

How's you idle?

--mike

 

Same

 

My idle has been fine. However, last night it got a little rough and at the same time the vac was showing around -15hg. Idle later improved back to normal.

This morning vac was -20hg. After a little beating, Vac settled back to around -15hg where it pretty much stayed the rest of the day.

I am wondering if when it heats up I am developing a small leak.

 

...and tonight its reading -14hg to -13hg. Pretty soon I'll be at 0!

Idle was a little rough too.

 

Once that vacuum leak gets bad it will be, lol. You probably have a small leak that gets worse as the temperature rises. Be careful until you diagnose the problem.

 

so a higher number in negative like -14 or -13 that shows signs of a leak ?

 

Positive pressure is boost and negative values in in/hg are vacuum. Normal idle vacuum is -20hg on stock compression. So if it gets to 0 then you have no vacuum (or a big leak).
However, since motors vary, it seems to be acceptable if it is stable and yet less vac than say -20hg. Hope that makes sense.

 

also, is there a way to calibrate a defi boost gauge, my buddy just went turbonetics and his defi gauge is sitting at +1 when the car is off, and shows he's hitting 10 lbs of boost, should only be getting 9 lbs with the turbonetics, plus headers and aftermarket exhaust,

 

Turbonetics should be 8.5psi out of the box though I have hit as high as 9.5psi.

 

So, this could suck. My E-01 always reads around -10 to -11 in. hg. at idle and it always has. Even my POS boost gauge I had in their when I first installed the TT read about this much.

I always thought that low vacuum meant loss of compression in engine or intake leak, but I just don't see either being very possibly with mine.

It always boosts perfectly between 5.4 and 5.6 psi (5.7psi spikes occasionally) and it has never had a lack of power that I can feel.

Also could it be because I am T'ing into both my wastegates. Maybe I will take my engine cover off and find out.

Any ideas?

 

If his gauge is reading +1 with the car off and the gauge on then he needs to definitely adjust it. Most electronic gauges read a 0 with the motor off. There should be an adjustment for the gauge somewhere. At idle 20hg is where you should be although it may vary. 35ounces find that leak man. Its got to be a coupler somewhere. Check the coupler at the intercooler inlet...

 

Ok just came back in from just putting the pressure sensor from the E-01 directly to the manifold and bypassing all T's to the wastegates and it still is reading -10 in. hg. at idle. I don't know why it is.

 

Ok nevermind I think.....

I have the E-01 reading in units of psi for boost, and just assumed that it read in In.Hg. for vacuum like most boost gauges, but a simple visit to a unit conversion website told me that -10 psi = -20.36 in. Hg.

So, I guess the E-01 reads both boost and vacuum in psi and just didnt' see that.

 

I usually see 18" -19" at idle with the A/C off. A/C on it drops to about 17".

 

i did the same thing at first, lol.

 

haha yeah, that will happen