Quote:
Originally Posted by raceyBMW
Yeah, didn't sound like the most efficient thing. In effect they are already using the work to do the compression, and taking that power away from the engine to do so, and then bleeding off some of the already compressed air. But I know a local guy who has a B8 S4, stock, and he is running very close at the local drag strip (Bandimere) to what he did with his stock 335xi....actually even a little faster maybe. That leads me to believe they do leave some headroom there.
BTW, most of the time in the summer months, we are actually running at about 9000+DA when we hit the drag strip...pretty much sucks.
Also, the thin dry air has less heat carrying capacity, so we can heat soak the FMIC easier than at sea level as well.
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In supercharges with internal bypasses, they don't use them to bleed off boost. But rather to circulate air between the charge pipe and pre-supercharger intake. Essentially eliminating compression and therefore reducing belt drive losses. Usually, the bypass is full open in moderate vacuum and then closes up as pressure approaches 3-4" of vacuum. At least this is how I've run them in Eaton roots style blower applications.