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Controlling the BOV
#1

Some 17 years ago Wessk posted a suggestion that the BOV be controlled by two pressure sensors (one in the IC piping and one in the intake manifold) to signal the venting of turbine discharge pressure. 

I have implemented a similar scheme using the Ford pressure switch found in some early turbo cars.  I believe a better solution would use a differential pressure switch to initiate venting, much as Wessk's suggested comparator circuit would.  I was never able to find such a switch that was also vacuum rated and of small size.

Wessk suggested a 4-5 psi differential would be a good setpoint for such a switch.

Has anyone had any further thoughts on the sensing points and/or the proper pressure differential setpoint?

Thanks for your indulgence during my trip down memory lane.  For autocross, I'd like to retain boost whenever possible, but my need for throttle response is greater than my need for torque. Hope to hear people's current thoughts on this.
'76 Capri for XP autocross,SVO motor,NPR FMIC,Merkur wire harness,E6,3" DP,AFPR,Boport cam & head, T5, Quaife LSD
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#2

I don't remember that, but it was a LONG time ago.....

Remember, fundamentally that is already how a BOV is controlled. One side of the diaphram is in the intake manifold, the other side (wheter simply the valve itself, or pneumatically the diaphram) is acted upon by the pressure in the IC pipe. The mechanical adjustments affect the differential pressure at which it opens.

For autocross throttle response, employing the antilag features available in ECU (no one uses it, but our PIMP has antilag) is much more effective than anything you can do with a BOV.
86 Mazda RX7, 2.3 swap, t5, MS3 sequential, BW EFR 6758
"If you can't dazzle them with knowledge, baffle them with bull sh*t"
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#3

Thanks WessK for your prompt response. Let me describe my feeble attempt to improve throttle response after brief throttle closure or part closure.

Upon throttle closure,  I have been using the pressure switch to open a normally closed solenoid valve controlling vacuum to the BOV only when pressure at the compressor discharge is above 5 psig . The protective action of the BOV is retained until the pressure switch drops out and manifold vacuum to the BOV is shut off.

I can see manifold pressure jump to about 1.5 psig as soon as throttle is re-opened, but not always.  I'd like to reference the pressure switch to the IC discharge line, as per your suggestion, but I'm concerned the (~3psi??) greater pressure at compressor discharge will jam up the compressor wheel and damage the shaft. 

Any further ideas or suggestions would be greatly appreciated.  I know your PIMP system has advantages, but I have not yet reconciled with re-doing all the wiring under my hood.

As as aside, the National XP champion pilots (like you) a turbocharged RX-7 II ... but with a rotary.  Tough luck for me he's also in my club.

Best, Rich
'76 Capri for XP autocross,SVO motor,NPR FMIC,Merkur wire harness,E6,3" DP,AFPR,Boport cam & head, T5, Quaife LSD
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#4

Depending on what BOV you are using, I believe they are adjustable and would accomplish the same thing you're saying.
If, big if, I am understanding what you're saying correctly.

I've got a Vortech Mondo BOV, it has an adjustable spring on it that can be tightened down to hold pressure to a certain amount before it opens.
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