Does boost measured read relative pressure difference, or absolute pressure?.....

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Jul 31, 2007 | 03:32 PM

cletus141

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Does boost measured read relative pressure difference, or absolute pressure?.....

I.e. does the computer compensate for elevation differences? Is it read as the difference between atmospheric pressure and pressure seen at the gauge? Atmospheric pressure at sea level is around 14.7 psi, whereas here in Reno, it's about 12.5 psi. So If I'm running 10 pounds of boost, would I have approximately the same power output as someone in LA running 7.8 lbs?

Thanks

Jul 31, 2007 | 03:41 PM

S4_Cinci (I S'edTFA)

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Boost is stated in gauge pressure, which has atmospheric pressure already subtracted out...

so the answer to your question is yes. Our engine will lose power at altitude, but not as much as a NA engine will.

Jul 31, 2007 | 04:21 PM

Andrew C.

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the boost you see in VAG or ECUx is absolute. as far as altitude corrections, not sure.

Jul 31, 2007 | 04:28 PM

Roque

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Boost is gauge pressure which is anything above the atmospheric pressure...

In your example you have the same absolute pressure going into the engine. If the outside temperature is the same, you would then have the same air density, and then the same mass of air entering the engine. Therefore the same power.

But, the turbos need to spin a lot faster to get the same pressure when the air density is lower at altitude. This is usually the limitation.