Bar is a unit of p ressure. It is useful because in engineering because it is related to atmospheric pressure. Atmospheric pressure is 14.7 psi = 1 Bar at sea level at 68 degrees F. Rounding off a bit here because I can't remember the exact pressure. It makes relating pressure to something real easier because any pressure could be represented as percentage of atmospheric pressure. A cool example of how it could be used is this. Turbos make more hp because of boost pressure. If a turbo boost gage says 14.7 psi, He will be making approximately twice the hp as stock (not really because there are other losses like heat) why is this? Well, this is why. At 14.7 psi turbo "gage" pressure this is over and above the 14.7 psi atmospheric trying to push air into the motor...So in actuallity you have 29.4 psi air entering the motor which is = to 2 Bar and low and behold the sled makes twice the hp. See in simplistic terms having atmosphere pressure in terms of Bar is useful?
One caveat here. In reality it is a little more complex because compressors raise the temperature of charge air. In reality the motor won't make twice the hp because well the sled is not at sea level and Atm pressure is not 1 bar. It is still not bad to calculate because there are some good adiabatic approxiations that take into account temperature and pressure both. Throw in a compressor efficiency factor and it is amazing how accurately you can predict hp. People use these concepts to "correct" dyno hp to standard temperature and pressure conditions so different dynos at different intake temps, pressure (altitude) can be somewhat compared.
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I swear you're all drinking beer from cans made from pistons I've recycled....
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05-11-2011, 08:39 PM
turbo
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