My 02 GT2 sometimes maxes out @ .8 and sometimes .9 why??thanks carl

 

boost is effected by ambient air temp and humidity and that could be part of it. Was the weather different when you got the two different readings?

 

no its the same. carl

 

Three things:
- Peak boost and your rpm/gear
- Air temp
- Diverter Valves

I'll start with peak boost:

I am not sure of the GT2's mapping, but peak boost on the stock turbo typically jumps up to .7 bar @ 2700pm in 3-6th gear and then drops off to .6 bar til 5800rpm where it climbs back up to .7 bar. 1st and 2nd really aren't in the rpm range long enough to get full boost. Also, you need to be in the higher gears as they put more load on the engine. More load = more boost per the time that you go through the RPM band. That is why you need to test in 5th/6th gear if you want consistancy.

Air temperature:

My car varies a good bit with temperature change. 70 deg might put me around .8 bar peak falling off to .7 and then .6 for a few before it peaks up to .7 at 5800rpm.

However, at 40 deg air temp, my boost climbs no higher than .7 bar while falling off to .6 rather quickly.

Cooler air is more dense with oxygen and thus, the turbos won't need to make as much boost to regulate the proper air/fuel mixture.

Diverter Valves:

If your valves are failing, that can result in lower peak boost. That is a simple fix.

 

makes sence it seems lower when it's cooler, thanks for the info. carl