SR20det in my S14 Vacum/boost problem

[TekonMotors]

I have a 1997 240sx with a S13 redtop Sr20det motor. My boost gauges reads -10 and then jups when im boosting. My question is there supposed to be any vacum at all???? thanks

[s13silady]

i think its supposed to read negative until you reach full boost.. can anyone else elaborate??

PS: this should be in tech talk ..:)

[mrmephistopheles]

vacuum is a good thing. it helps you brake among other things.. that's kinda the reason your guage even has a vacuum sweep to it.
Short & simple, there doesn't seem to be anything wrong.

[Jeff240sx]

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=2415769197&category=38660
That gauge doesn't have a sweep!

Anyway.. you should read about -20 to -25 psi vacuum at idle. If not, you've got a problem. After that, it rises, as a motor is nothing but an air pump, and it draws air. In a NA car, you'll hit 0 psi, which is the peak VE of the motor...
On boost, you'll read positive pressure, as air is crammed into the motor.
So, vacuum is fine. -10psi vacuum is not fine, however.
-Jeff

[TekonMotors]

Confused......

At idle it is -10 and boost over 10. You get what im saying. thanks to al tha reply....

[JiinKz]

Personally i'm used to reading vacuum in "inHg" or "mmHg"
All of the SR's that i see run around 15-17inHg of vacuum when you're idling (equivalent of 375-425mmHg). If your boost gauge reads vacuum in inHg, and you're only registering 10inHg you've definitely got a leak somewhere. This was my case as i had a lack of throttle body gasket when i first got my engine ;)

[uiuc240]

Originally posted by TekonMotors
Confused......

At idle it is -10 and boost over 10. You get what im saying. thanks to al tha reply....

Sounds to me like your Autometer gauge is out of adjustment. Take it out of the pod, pop the light bulb out, and use a small screwdriver to push or pull the metal ring that you see in there. Adjust it so the gauge reads "0" psi when there is no pressure signal.

If it's already adjusted correctly, then you have other problems. You should be getting 15-20 inHg of vacuum and ~7 psi of boost (if the wastegate actuator is stock and you don't have a boost controller).

Eric