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      08-31-2012, 05:21 PM   #51
M3PO's Avatar

Drives: '08 IB E92
Join Date: Sep 2011
Location: OC

iTrader: (7)

Originally Posted by RussRamz View Post
This is a great discussion. I have learned quite a bit, but I don't understand how (if at all) supercharger systems on these cars compensate for cooler than normal temperatures. A standard atmosphere is 15 C at sea level. If the supercharger system is designed for X amount of boost maximum, are there any safe guards for cooler than standard days at sea level, or do you just have to monitor the boost level yourself so that limits aren't exceeded? At altitude, temperature really effects the atmospheric pressure. For instance, here in El Paso, I am sitting at 3,948 feet. A standard day at this elevation would result in a temperature of approximately 7 C. This doesn't happen in the Summer months and we usually see 30-35 C in the afternoons. Right this instant at 10:43 AM with a temperature of 27 C, dew point of 3 C and a barometric pressure at 30.13 results in a density altitude of roughly 6,075 feet!

Now on the other hand, place yourself at sea level, winter months and you can see -2000 feet which would raise boost pressure possibly above design limits, no? What's the safeguard for this? I'm asking because I don't know and want a car designed to function in all types of environments (hence my reluctance to supercharge).
SC boost varies with density/pressure. Temperature and altitude both effect density/pressure. Therefore, the ambient temperature will effect the boost pressure. The SC spins at a fixed RPM (unlike a turbo) governed by it's mechanical connection to the engine. It has no control over the boost pressure that it's producing. The engine must be able to "absorb" the differences in boost pressure by adjusting fueling and timing.
2008 IB E92 M3| BBS | KW | Arkym | Platte Forme A.G. | Active Autowerke | K&N | Fabspeed | Dinan | Evolve-R