Quote:
Originally Posted by DorkMissile
Understand that by reading boost thru the OBD port will be a "theoretical" boost reading.
It is reading the MAP, then subtracting Ambient Pressure from it to give you the remainder of what is left over.
If you want a gauge just so you have something to watch go up and down, and show relative pressure, it will suffice. If you want something accurate, you will need either a mechanical gauge or use a gauge with a sensor.
On my car the ambient pressure will change by 1lb or more just by the car moving (air pressure building at the front of the car) if you log it.
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With the PD blower, he's probably getting baro from the stock MAF that is before the throttle body. Then the TMAP is giving manifold pressure, so subtracting the MAF's baro reading from that.
On your centrifugal supercharger, do you have a baro breakout kit? I bought one because with the MAF sensor mounted inside the intercooler, the baro readings were messed up. Yes, saying they would change, but they shouldn't be doing so. With the baro breakout, and having the second MAP mounted in open air to the wiring harness on the engine, I checked a log from the dragstrip. Found that the baro reading just before I started the run was the same as it was at 125mph at the 1/4 mile mark. Checking other points during the run had the same reading every time.