Quote:
Originally Posted by Irace86.2.0
You completely missed the context of the conversation. We were discussing the use of the bypass valve as a wastegate to bleed boost like turbos bleed exhaust, so someone could run a smaller pulley, but not hit high boost. Essentially they would bleed boost so boost would be flat instead of building with rpms. I was saying this means that if the supercharger is hitting 10 psi from 4-8k then it is spinning twice as much at 8k than at 4k while only producing 10 psi, so at 8k the engine is working harder creating more heat and is less efficient than it is at 4k. It is over-spinning while the bypass valve is open and bleeding/wasting boost. Turbos don’t waste boost, which is why they are much more efficient when doing boost-by-rpm/gear/map.
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Turbo's use similar recirculation valves in addition to wastegates. Sure, precisely designed turbo systems could omit the valve if the
compressor can withstand the surge within design limits. Recirculation valve can also be omitted with a supercharger in the same way.
That overspin is not a disadvantage of supercharger. Actually it can be an advantage that eliminates the turbo lag. Plus, when the recirculation valve is open, supercharger's parasitic load on the engine becomes minimal since the superharger does not need to work against the back pressure of engine intake.