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01-04-2004 12:41 PM #1
Huh? Error is Corky\'s Maximum Boost?!?
I am calculating to understand the turbo setting, with an excel sheet and Corky Bell's book Maximum Boost. I read page 26, about the pressure ratio. Here he says PR = (14.7psi x 'boost' psi) / 14.7 psi. The 14.7 being atmospheric pressure. Going metric, I simply say PR = (1 bar + 'boost' bar) / 1 bar. Therefor PR equals absolute pressure. But a few lines lower he says that PR = 1.82 means 1.82 bar infeed pressure, which 'is much to high to cover in this book'. But he came to the 1.82 PR by starting with 12 psi of boost, which he describes earlier as acceptable. Huh? I think even the teacher has absosute and 'gauge' pressures mixed up, here..... Besides that, the 1.82 PR is often in the middle of the Garrett efficiency tables of many turbos, so I think it is not such a weird figure to aim for. I agree 1.82 bar infeed pressure is a lot, because it is PR 2.82, not 1.82 as described in the book.
Feel free to correct me if I'm wrong, I'm only learning!
01-05-2004 03:41 PM #2
Re: Huh? Error is Corky\'s Maximum Boost?!?
First off Flow charts are in absolute pressure so 1.82 is .82 bar gauge.
Second PR is not the only thing to consider, the bottom flow rate is more important in turbocharger selection. If you want to choose a compressor then you go from flow rate, very roughly multiply the flow rate (lbs/min) x 10 and you have HP, then move up and see at what PR its most efficient. You can then calculate your engine's boost requirement to reach that HP target.
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