Quote:
Originally Posted by Cory S
Actually, when people say you are getting more power from the same PSI, it's because they seem to forget that the same PSI peak is being up in the higher RPM range, where the engine consumes more air and is more efficient also. Yes, the charge will be a little cooler, but that's what the intercoolers are for also.
So a stock N54/55 at 17psi at 4600rpm may be very close in output, but the larger compressor keeps holding pressure higher in the RPM range after that. That's where the output peak is increased.
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No, that isn't the only reason it can happen. If you ran same boost curve on both turbos, the ps2 would still make more power. It can happen because of being able to hold boost higher, but if you take a smaller turbo that is getting to the edge of its efficiency rating (like the N55 stocker or ps1) and compare it to the PS2, you will get a much lower outlet temp. Yes the intercooler lowers the temp, but it isn't near 100% efficient and you will end up with lower AIT with the larger turbo. This is also a huge benefit of meth/water/nitrous injection.
Quote:
Originally Posted by Rob_BMW_PNW
Not all PSI is created equal...
The wheel and inlets/outlets are larger, how is it 'the same'?
How is temperature lower on a bigger turbo?
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That is not correct at all, pressure is pressure. It is just a reading, so yes all PSI are equal. Now, that is not all of the equation that we are interested in. The equation is PV=nRT. R is a constant and N is the amount of the substance, so we can take them out for comparison purposes, so PV=T. What we have left is pressure * volume = temp. We know the volume inside the turbo tract is constant, so we can take out volume too. That means if we lower the temp, the pressure will also lower. So the same amount of oxygen is available for combustion at a lower pressure if we lower the temperature. A 20*F drop in IAT's will be an increase of 4% in power at the same boost level.