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Discussion Starter · #1 ·
I currently have the heavy duty BOV from Bosch installed on my car but I am concerned about the back pressure from the recirculation air going back to the Throttle body. My question is what do I use to seal off the opening for the return line in the pipe that runs from the outlet side of the IC to the Throttle Body? I am sure someone has faced this mod before and I would appreciate any help it getting my Atmospheric BOV installed.
Thanks!
Regards,
John
 

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If you seal the tube that comes off the intercooler to throttle body pipe, your BPV will do nothing and you'll end up with compressor surge (BAD BAD BAD).
If you want to convert the BPV to BOV, I suppose you could just plug the hole on the compressor side of the turbo (where the BPV routes bented air) and add a filter to the bottom of the BPV (as it draws air in under vaccum). But there is hot and heavy debate as to whether or not BOV is bad vs. BPV.

Hope this is more helpful than confusing.
 

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Discussion Starter · #3 ·
Thanks for the response. It looks like I need to check the plumbing a little more closely. Can you tell me what the contriversy is over the BPV vs the BOV? I have been told by more than one source that the Atmospheric is the way to go for two reasons. One, it allows the turbo to spool up faster after shifts. (and with an auto thats important). Two, it prevents recirc air from causing back pressure against the turbine blades that may cause damage. Is this wrong?
Thanks,
John
 

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What you've been told is wrong.

You drive a 92 9000 (if your profile is correct) this car has an airmass sensor. If you attempt to install an Atmospheric dump valve on this model - your car will not idle properly, the mass sensor won't know what the heck is going on and things will generally go down hill..

The purpose of any type of by-pass valve is to stop a compressor stall (and thus possible turbine failure) and to keep it spinning to reduce lag.

A new bosch unit will accomplish that better than a shagged out one.. however it's still a diaphram design.. I've got a Forge Motorsport piston recirculating dumpvalve in my '92 - it handles higher boost levels, lasts longer and if an performance airfilter element is installed.. you can still hear the woosh, as it sneezes into the airbox...
 

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If you attempt to install an Atmospheric dump valve on this model - your car will not idle properly[/b]
Not true with a twin piston atmospheric, which most decent designs seem to be these days - these stay clamped firmly shut at idle, therefore no leaks. The problem arises on cars with air mass meters (AMM), and that includes all Trionic 7 cars as well as the earlier stuff, in that the atmospheric valve dumps air that has already been metered by the AMM. Therefore, on gear changes/lifting off etc. the engine temporarily gets less air than it thinks it is getting, leading to a momentary rich condition and the possibility of stumbling and general crapiness until things recover. I say 'possibility' because it doesn't always seem to be the case: I have seen atmospheric twin piston valves work happily on cars with AMMs, including early 9000s and a 99t with the old mechanical K Jet metering system.

AMM issues aside, there is absolutely no difference in the effects of using one vs. the other apart from the noise.
 

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Discussion Starter · #6 ·
OK Mark and Julian!
So basically the recirc model from Forge is better than my upgraded Bosch and there is no difference between a BOV and a BPV except noise. I had planned to purchase the Forge BOV anyway so maybe the bypass/recirc unit from them would be a better choice for me to avoid problems. Thanks for the responses and I will do a little more research to find out what I can on the issue.

Regards,
John
 

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The Bosch BPV, if new and the car hasn't been tweaked for higher boost, should be fine for a fair while. However they can leak if boost is increased and over time the rubber diaphragm deteriorates and eventually splits.

The Forge valves, being aluminium, won't degrade and as Mark says, can handle higher boost. You might find that a Forge BOV works OK but to be 100% sure go for the BPV as this will be a straight forward swap for the Bosch unit. To answer your original question, if you opt for a BOV you can get a 1" blanking cap from Forge to plug the return line hole in the inlet. Alternatively a 1" hydraulic pipe cap works just as well (but isn't as shiny )
 

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Discussion Starter · #8 ·
Thanks Julian,
I am talking to Tom Porter at Forge Motorsport USA next week about an upgraded waste actuator for my 9000 and have also emailed him in regard to the BOV/BPV issue and I will let everyone know what he has to say about the issue.

Regards,
John
 
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