BOV vs Bypass Valve
Thread Starter
SSU'S Vice Mod
Joined: Jul 2004
Posts: 2,391
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From: Hazard Co. Maryland
BOV vs Bypass Valve Is there really any difference? I'm assuming it's just like a turbo vs. a supercharger, same end means (forced induction) just two different ways of getting there. Was cruising Jose's site and happened to pick up on that and it left me scratching my head.
FormerVendor
Joined: Dec 2001
Posts: 2,444
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From: WWW.SPEEDINC.COM
From another post-
"A bypass valve is normally open under engine vacuum (idle and cruising) to allow air being moved by the supercharger to freely bypass to atmosphere or recirculate.
This is necessary as the supercharger is mechanically attached to the engine, therefore compressor speed and airflow is directly related to engine RPM.
When you put a blow off valve in place of a bypass valve, (which is normally closed during engine vacuum, idle, cruising, and only opens after throttle is closed during a boosted situation), the air being moved by the supercharger has nowhere to go as it cannot freely recirculate or bypass the system. Now when you are idling and cruising, the supercharger is in a constant state of compressor surge, and if enough pressure is built up, the BOV will start 'chirping' while pressure is escaping past it.
What this does is heat up your intake air charge, as it is constantly being compressed, and also, it is annoying as hell.
A turbochargers output on the other hand, is completely load-dependent, so there is no excess air that needs to be bypassed during idle/cruise conditions. You don't even really "need" a bov with a turbocharger, but when you close the throttle during a high boost situation, the pressure surge between turbo and throttle blade will cause compressor surge (which could possibly damage the turbo over time), and on a stick shift car, it will slow down the turbine to the point that lag will be increased during shifts. If the excess air can be 'blown off' during shifts, the compressors will not be dragged down as much and will come on line much faster after selecting the next gear."
"A bypass valve is normally open under engine vacuum (idle and cruising) to allow air being moved by the supercharger to freely bypass to atmosphere or recirculate.
This is necessary as the supercharger is mechanically attached to the engine, therefore compressor speed and airflow is directly related to engine RPM.
When you put a blow off valve in place of a bypass valve, (which is normally closed during engine vacuum, idle, cruising, and only opens after throttle is closed during a boosted situation), the air being moved by the supercharger has nowhere to go as it cannot freely recirculate or bypass the system. Now when you are idling and cruising, the supercharger is in a constant state of compressor surge, and if enough pressure is built up, the BOV will start 'chirping' while pressure is escaping past it.
What this does is heat up your intake air charge, as it is constantly being compressed, and also, it is annoying as hell.
A turbochargers output on the other hand, is completely load-dependent, so there is no excess air that needs to be bypassed during idle/cruise conditions. You don't even really "need" a bov with a turbocharger, but when you close the throttle during a high boost situation, the pressure surge between turbo and throttle blade will cause compressor surge (which could possibly damage the turbo over time), and on a stick shift car, it will slow down the turbine to the point that lag will be increased during shifts. If the excess air can be 'blown off' during shifts, the compressors will not be dragged down as much and will come on line much faster after selecting the next gear."
Thread Starter
SSU'S Vice Mod
Joined: Jul 2004
Posts: 2,391
Likes: 0
From: Hazard Co. Maryland
Ahhhhhhh, thank you sir. That's what I thought I just wanted to be sure and see if you could use a bypass in both instances. I suppose you could recirc to a turbo but there isn't much sense in that is there?
