SamGrant951

17-18ish

cpt_koolbeenz

Howdy-
I am sure the reading is accurate (I checked it with two different gauges at two different spots). My ISV leaks a bit (I can suck through it, but not enough to "breathe" through ). I was thinking about removing it and seeing how that works out with AC being on etc... I am beginning to understand the "volumetric idle system" but not totally.

The BOV that leaks at idle is the SAAB/993 one. It is brand new. I think that is normal. The HKS SSQV was either not opening fast enough or not enough on boost. I could hear some air rushing back out the turbo and some coming from the BOV, but it was not loud by any means (from the HKS). So I took it apart and oiled it... Everything looks fine inside. However, when I suck on the vacuum port of the HKS, I can suck a very, very small amount of air out. I think that is due to the fact that HKS uses a valve to let pressure equalize between the vacuum side of the diaphram and the other side of the same diaphram. I tested the HKS wih out the outer shell on it to see if it moved when I revved the car (in neutral) and slammed the throttle shut... It opened to its full travel when I did that. So I think the HKS "works" but haven't tried it on the car again since I oiled it. Personally, after taking it apart, I don't like the design of the HKS BOV. Its technology is not exactly "cutting edge." I would have thought they would have used the boost pressure on both sides of the valve to keep it shut along with a small spring. That would allow the vacuum to activate it faster and with less negative pressure. I think I may sell the HKS and try an Apexi dual chamber later on...

So I gather my vacuum reading is normal based on the age of the car and the high altitude...

(Sorry for the long post and HKS hijack)

sean.

I'm reading a cold @ 10-11in and then 16-18in when warm. At decel the vac reads about 20-21.

Sort of suprised to see such high numbers from the rest of you guys. I must have a vac leak somewhere. The boost on the car has always been a little low (10 lbs)...I always thought it was a weak wastegate.

Is it possible that it is something else? Thanks

-sean 86' 951

Danno

On a really worn-out car with 180k-miles, I was seeing about 10-12 inHg. of vacuum at idle. After I rebuilt the engine, we were getting 20-22 inHg. vacuum. On decelleration overrun, it would hit 24-25 inHg. vacuum; close to maximum on the gauge.

toddk911

How much should the vac readings drop when the ac is engaged?

schnellfahrer

After putting in Lindseys hose kit (small hoses, not the ones under the manifold) I'm seeing 19-20hg at warm idle, which is slightly lower than before replacing the hoses. At decelleration I'm seeing 25-26hg.

streckfu's

12 when cold and 21 warm

Mikeaagesen

Wow, I am only pulling in about 15-16 on a warm idle at whatever altitude Iowa is. Maybe I should update that birds nest under the manifold.

JustinL

If there is one thing I've learned from tuning the link module and fiddling with the idle, it's that the vacuum reading is also very dependant on the idle screw on top of the throttle body. I'll bet many people with low vacuum have had the screw work it's way out a bit and then the DME compensates to keep the idle at the proper level. I've had anywhere from 31 KPA at idle all the way to 38 kpa. That translates to a range between 18 and 21 inHG at sea level (101 Kpa). But up in Edmonton, our atmospheric pressure is usually around 92 KPa, so on an autometer gauge, it would read 16 and 18 respectively.

Justin

Edit-- Anybody hit 29.92 yet?