Determining boost levels from the MAP sensor readings
 

This all started here:

So I found what I think is the formula to determine boost from the MAP reading: boost in psi = (SAE.MAP in kPa - 101)/6.895. So according to this the boost I was hitting then was 3.48 psi. **101 kPa is approximately the barometric pressure at sea level.

When I took the car out on Monday, I hit 157 kPa on the MAP sensor, so that works out to 8.12 psi of boost.

Now as for the SAE.MAP value in the data page of EFILive, which shows a MAX of 22.5 psi, pressure at sea level in PSI is approximately 14.7 psi. So subtracting 14.7 psi from 22.5 psi gives us 7.8 psi of boost. Plus or minus...

Which gives a formula of: Boost in PSI = SAE.MAP in psi - local barometric pressure.

I'm presuming the barometric pressure here is approximately sea level, but obviously that value will change depending on the local weather of the moment somewhat.

So the error I was making trying to determine the boost was because I wasn't paying attention to the name of the actual sensor being used to determine boost: MAP Sensor = Manifold Absolute Pressure Sensor. It's NOT a relative pressure, so barometric pressure has to be taken into account.

OK, so I learned something today.... :thumbsup: