JimLecesse

Warning: extreme "newbie" question

I have a 1988 944 Turbo, bone stock. I've been searching everywhere for information but I've heard 4 different answers..
Regarding the turbo bar gauge in our cars, what does 0.4, 1, and 2 bar really mean in terms of PSI. I know a good deal about turbo cars, but in the past I've always figured 1 Bar to be around 14.7 psi. When at WOT, my bar gauge reads about 2-3 lines past "1 bar" yet I've heard stock boost is around 11 psi?
I'm so confused LOL

thanks
Jim

hosrom_951

Anything under the 1bar is negative pressure, at 1 bar, that is absolute pressure (zero), anything above 1 bar is positive pressure (that is when the turbo kicks in).

The stock gauge reads the manifold pressure, not the turbocharger. The stock gauge is also inaccurate (what everyone says), so get an aftermarket boost gauge, hook it up to the KLR feed line to get accurate reading from the turbo.

Waterguy

1 bar = 14.5 psi. Atmospheric pressure is about 14.7 psi at sea level, so 1 bar absolute on the gauge = no boost over atmospheric. 0.4 bars on the gauge = about 18 inches of mercury (in. Hg) of intake vacuum. Stock boost for a 951 is 0.75 bar or 11+/-1 psi, which reads as 1.75 bar on the stock gauge. Depending on the year of your car, the stock boost peaks at 3500 rpm, then on the older cars it gets dialed back to 0.5 bar (7 psi) by 5800 rpm. the Turbo S/1989 cars make more power because the 11 psi boost is held to 5800 rpm. Hope this helps.

PS. Welcome, and add the year/model of your car to your signature in your user profile.

BTERRY951

So pardon my ignorance but my bone stock just rebuilt car shows 1.4 to 1.5 on the gauge at full boost. should it be higher?

Oddjob

Yes, should be around 1.8 bar peak on the gage (1.75 bar abs) mentioned in the above post, but the dash gages are relatively inaccurate, so you will want to double check the actual boost level w/ a known/good gage before determining that you do or don't have a boost problem.

BTERRY951

thanks!!

gmsracing

My car is showing about 1.5-1.75 on the stock gauge but it is showing 15 psi on an aftermarket gauge. I'm not quite sure which one to trust as, honestly, I thought the car should be faster than it feels. I think I need to get another gauge to make sure everything is correct.

Willard Bridgham 3

The gauge measures psia, absolute pressure, therefore, 1 bar = 14.5 psia.

My stock gauge measures the same as my large dial VDO gauge which is calibrated. The stock gauge is accurate, it just suffers from parallax problems and too small a face.