Thread: New type of BOV
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beepbeep beepbeep is offline
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Join Date: Jun 2001
Location: Sweden
Posts: 5,714
It's a BOV, for gods sake. A thing that should recirculate the air when you lift of the throttle. This is starting to sound like a thread from "Fast & Furious" forums

BOV doesn't give any more power. It's shut when you boot it. OEM BOV works fine, it's just a bit overengineered.

Also, I'm very sceptic about turning BOV into pop-off valve. As soon as you get bleeding metered air in a car equipped with anything else but MAP (of MFI) the engine runs richer than it should. You make turbo pump air that's being dumped overboard, essentially burning fuel to pump air oboard.

I'm actually using this valve right now as a wastegate AND a diverter valve simultaneously, that's right a wastegate and blow of valve at once,...............controlling the boost pressure(25psi) by bleeding off boost pressure at the charge pipe rather than using wastegate control. The turbocharger wastegate is set at ~29psi...which allows the turbocharger to operate at it's max efficiency while the SE diverter valve regulates the boost pressure at 24psi to the motor for the proper tuning. Show me another DV that can do this..........
I find this particulary funny. How the heck do you make turbo "work at it's peak efficiency" by letting it pump air and then throwing away a portion of that air overboard? Sounds like a nice way to overrev the turbo and let the engine run rich. If this was true you could remove the wastegate alltogether and just control the boost by pop-off. The reason you don't find "another BOV doing this" is beacuse you don't want it to do this.

Wastegate is there to limit the massflow trough turbo, limit it's RPM and lessen the backpressure. You don't know if "turbo is working at it's peak efficiency" wothout knowing exact compressor map and the mass flow for turbo involved.

I won't delve deeper into issue but let me say that regulating boost by pop-off valves belong to early days of turbocharging history and should stay there.

Only production car that regulated the boost this way I saw was an old Mitsubishi Pajero Turbodiesel. It didn't have the wastegate and just let the turbo deadhead and then had the pop-off set slightly in the middle to get rid of excess boost if turbo should happened to boost little extra on a sunny day.

So to wrap it up:

You control the boost with wastegate, period. It's the best and most efficient way to do it. That makes sure it doesn't spin more than it should and that all metered air goes into engine. It also means you don't have uncontrolable air leak which must be compensated by fuel-injection should it occure.

You control transient overrun boost peaks with BOV. That's why it's there. It's used only for that and it's main function is to prevent harmful boost peaks. It doesn't make more power otherwise. It's closed shut during WOT. Last ten years it found a new use, to make funny sounds which makes car sound "racey" which spawned a whole slew of cottage industry making "funny sounding thingies" that don't make any difference and if wrongfully configured, and sometimes cars run rich.

Exuse me for sounding like all-knowing ingorant prick but there is a substantial reasoning behind manufacturers fitting wastegates and BOV's to their car and not making them sneeze or bleed boost into air.

Thank you for your time,
Old 01-28-2008, 03:42 AM
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