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      04-11-2010, 03:39 PM   #5
M&M
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Drives: E92 M3 Competition Pack
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Quote:
Originally Posted by e.n335 View Post
A centrifugal type supercharger does not provide absolute boost like a turbocharger, it provides relative boost due to the fact that the speed of the compressor is directly related to the engines rpm.
A super provides "absolute boost" just the same as a turbo does. A CF blower and turbo are essentially the same except one runs off exhaust gasses and has a wastegate and the other runs off the crank. I don't follow the second part of the sentence. Due to speed of the compressor being related to the rpm? The rpm range is the same at sea-level or at 5000ft. The car will rev from idle to 8500rpm at both elevations. So every revolution of the crank will produce the same amount of boost and spin the same amount of air into the engine at sea-level and at altitude.

The difference being that the air is less dense up here. 17% less dense. So you are increasing the power from a much lower base. And the extra air you are spinning in is also deprived of oxygen compared to sea-level due to the air being thinner and less oxygen rich. So I think Roman will run a smaller pulley due to the engine being nowhere near the limit of power one gets to at sea-level. You are starting with a 50hp deficit so one can run more boost safely up at altitude.
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