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      01-22-2013, 09:37 PM   #51
Gearhead999s
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Drives: E93 335is(wifes)E92 M3 SQ5
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Quote:
Originally Posted by CSMRX7 View Post
Superchargers don't compensate for altitude like a turbo. They are pulley driven, so if pulley size is the same the boost pressure is the same. Unlike turbos which are controlled by wastegate which will maintain a constant absolute pressure and compensate for the thinner air of altitude.

This is of course a massive simplification, as we assume no efficiency losses as the turbo runs hotter (ideal compressor map) and the altitude also reduces spool time for turbos. But the point is the SC don't see the sme benefits as TC.
Do these superchargers not have a bypass valve which is effectively the maximum manifold pressure control?If I remember properly these are are controlled by the ECU to control boost when the throttle is closed & maximum boost level which is also determined by pulley size.I have not owned a S/C car in over 20 years so maybe this is all an out of date technology.
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