01-10-2017, 02:41 PM
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#29 (permalink)
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Base Member
Join Date: Jun 2013
Location: Sydney, Australia
Posts: 230
Drives: '09 Z34 BP Turbo V2
Rep Power: 26
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Quote:
Originally Posted by TopgunZ
The reason they have to is because a SC is tied to the revolutions of the motor so it is basically making boost all the time. When you are at 7000rpm and let off the throttle, and the supercharger is still spinning at 50,000rpms....where do you think that air would go?
Even at idle the supercharger is still spinning and the air it is pushing has to go somewhere. The engine is set to ingest what fuel it is seeing for a good AFR so it cant keep swallowing air.
Every and all centrifugal superchargers are like this.
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I understand that a SC is constantly flowing air due to being belt driven and subsequently always making the 'bov noise' whenever you let off the throttle.
What I didn't get was the actual operation of the BPV in an SC application. The more I'm thinking about it though, I think I'm starting to get it. Under idle condition you're seeing vacuum in the intake manifold, and if the spring inside the BPV is weaker, it is just enough vacuum to barely keep the BPV open. Under acceleration depending on how much throttle applied the intake manifold would see little vacuum or boost, both of which would overcome the weak spring and close the BPV. Let off the accelerator and intake manifold sees normal vacuum and BPV opens again.
If that's the case, then theres no major difference between Turbo and SC application, aside from adjusting the spring inside a BPV used for SC application to remain slightly open at idle.
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