Originally Posted by RiXst3r
Can't use a generic obd gauge to read boost on the n54... The map sensor on the manifold of the n54 is only good for 3.3psi or so... the 17 you see is not subtracting ambient pressure of 14.5(or so).... The T-map sensor before the throttle measure up to 22psi, the ECU reads both these and does a blend of the data.
On the n54 it's best to use a vacuum driven sensor (which is what we use for the p3cars.com gauge for the n54 and 1M)... otherwise you won't see vacuum and the throttle plate will create spikes to the sensor that are never seen in the manifold... makes for crappy peak recall!
The n55 on the other hand has a 22psi capable sensor on the manifold so obd data will show actual full boost.
We've sold a few gauges to 1M users... I am assuming they have been running them and should be able to report back actual boost,egt,coolant temp,AIT,0-60 times, etc... all the stuff the P3 gauge reads.
I'm pretty sure not all n55 engines have a 22 psi sensor, as mine won't give a reading over 3.0x psi.