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Dialling in Centrifugal Blower BOV @ Idle

Practical Dyno Tuning

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I've always wanted to know what is the correct method or best approach for this and at which step in idle tuning process do I adjust the spring inside the BOV to bypass air (do you do it before adjusting fuel and ignition?) and how do I determine how much to open it up by instead of just guessing this?

Obviously this will affect idle setting to some degree as it controls the volume of air the engine consumes at idle. Is venting more out the BOV at idle more fuel efficient or does it sacrifice torque in stop start traffic driving?

Its not a topic i've ever discussed with my tuner to be honest.

I'm not sure what your question relates to (4:45 am here and well past bedtime...) as, while I'm not that familiar with automotive applications, centrifugal (aka inertial) blowers will effectively stall if the inlet, or exhaust, side is closed, and at low rpm they have low efficiency, anyway, with internal leakage adding to that. I would expect there to be no reason to have a blow-off valve for anything other than high rpm operation, at high throttle openings, to prevent overboosting.

I understood the BOV was only used in high-RPM throttle closed operations. So I would think you would set it above the max boost you expect to make.

Hi fellers, you are both correct that you need it for high RPM and closed throttle situations. That's so it doesn't throw a belt with compression surge, but Centri blower's also need to have the BOV/Bypass valve slightly open at idle at all times. They produces too much air for the engine to consume and stall without one. Even though they produce more air than the engine can consume at idle, you will find its not enough pressure to open most aftermarket BOV at idle because of the spring tension within the BOV is to strong. Often you have to go a softer spring within the BOV to remain open at idle on a centri blower setup.

What I'm wanting to know is a bit more idle tuning details around the opening positioning of the BOV?. What are the affects of idle stability and fuel usage say if the BOV was more towards the open side & vice versa of it being more towards closed side.

It will likely absorb less power compressor stalled but you don't want it surging. If the bov is after intercool as close to the throttle as possible you could run a very light spring and still have it close at high rpm open throttle.