My theory on why a BPV is necessary with stock CIS system..
03-22-2006, 01:02 PM
#14
Here is another way to think about it...
since air is a fluid then consider pouring some water into a tall cylinder. The water you are pouring in represents the column of air entering the motor. If the cylinder had no bottom the column would pass right on through. the bottom of the cylinder represents the TB valve in a closed position.
When the water hits the bottom there is still more water trying to get in (forced by gravity instead of a turbo). As the cylinder fills the level of water represents the shock wave travelling back through the intake system. the first inch is the MM hose, then the IC and so on.
Since the water represents the compressed air then if you imagine a BPV in this case it would be an atomiser. The backed up water exits the cylinder and gets atomised into the atmosphere. before it condenses and is turned back into a stream of water. It is also a little more dense than the water vapor in air was to being with.
Knock the bottom out of the cylinder (open the TB valve) and the water exits as it should. the small amount that the metering is off by is only the amount of water up to the BPV location.
Did that help or is it more confusing?
When the water hits the bottom there is still more water trying to get in (forced by gravity instead of a turbo). As the cylinder fills the level of water represents the shock wave travelling back through the intake system. the first inch is the MM hose, then the IC and so on.
Since the water represents the compressed air then if you imagine a BPV in this case it would be an atomiser. The backed up water exits the cylinder and gets atomised into the atmosphere. before it condenses and is turned back into a stream of water. It is also a little more dense than the water vapor in air was to being with.
Knock the bottom out of the cylinder (open the TB valve) and the water exits as it should. the small amount that the metering is off by is only the amount of water up to the BPV location.
Did that help or is it more confusing?
03-22-2006, 01:48 PM
#15
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LOL it helps, but......
I can state unequivocably that I was having a problem before adding the BPV (both with the stock ECU and the chipped setup), that miraculously went away after the addition of the BPV.....
Is it possible that the sluggishness that I was seeing after shifting from boost is actually caused by something else that is not working properly? maybe....
I have not had a chance to drive another turbo 5000(stock setup), so I can't say for sure that it is the same......
Logically, though, it would appear that the build up of pressure has got to cause some problem, even if only momentarily (for me it seemed to last for more than just a second or two)..
If anyone has an idea of what part failing would cause this, I'll be happy to listen...(if it's not just the stock setup)...
Is it possible that the sluggishness that I was seeing after shifting from boost is actually caused by something else that is not working properly? maybe....
I have not had a chance to drive another turbo 5000(stock setup), so I can't say for sure that it is the same......
Logically, though, it would appear that the build up of pressure has got to cause some problem, even if only momentarily (for me it seemed to last for more than just a second or two)..
If anyone has an idea of what part failing would cause this, I'll be happy to listen...(if it's not just the stock setup)...
03-22-2006, 02:04 PM
#16
Is it possible you nudged something when doing your install? Air temp sensor?
No question the car will run a little smoother with the addition of the BPV. I really didn't notice all that much when I installed mine but I know that it is helping. I suppose the fueling settings have a pretty large impact on how much the BPV will affect things.
Either way... BPV = Good investment
Either way... BPV = Good investment
03-22-2006, 02:56 PM
#18
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Re: LOL it helps, but......
Definitely not to argue that you were having a problem, but it probably was not because of the stock system design.
Your theory on what was happening actually makes sense, but the deceleration valve compensates for the components fighting as you envisioned. It's essentially a BPV for the CIS air metering process that eliminates the stalling of airflow that you described so there should never be that momentary lean condition that you were thinking of. It acts as a throttle controller that allows the engine to dissipate the pressure gradually as you come off the throttle and revs drift down while preserving the previously metered A/F ratio... At least that's how I understand it...
The BPV issue in general is a little different. Check out this pic, clipped from SJM:
<img src="http://www.sjmautotechnik.com/trouble_shooting/ecupic/bypassv.jpg">
As you can see, what the BPV does is to create a feedback loop. Imagine boosted air rushing from the turbo, and then the throttle valve snaps shut. Brick wall. The turbo gets a jolt and spins down more quickly because of the trapped (and increasing) pressure. When the BPV (also called a "diverter" valve for reasons that should be making sense!!) feels vacuum behind the closed throttle, it pulls open and allows the boosted air to take a few laps around the turbo. Throttle opens, BPV snaps shut. Voila. What you get is less turbo lag between shifts and less wear and tear on the turbo.
So, it's hard to imagine that the lack of one would be causing your slugishness / driveability... The stock 10v turbo is so mildly boosted that this problem is almost transparent, so that's why (I guess) Audi thought they could get away without one... Adding one to a properly running car MIGHT be noticeable, but my guess is not by much. No personal BTDT, but think about it -- the only time it's an issue is at WOT making full boost and only for a split second as you shift... That's when you might feel a half second quicker return to full boost. Otherwise, most of your casual driving would be unaffected with the turbo in vacuum (or in a miniscule way at 1.1, 1.2, 1.3 bar...). Watch your boost gauge as you drive around, and you'll see that it doesn't really dip into the boost all that often. Of course, I guess that depends on how heavy your right foot is!!! Mine can be pretty heavy!! LOL... You can definitely tell in more heavily boosted cars, though. Big time.
So, from what you said, you're not hitting 1.4 bar? You should definitely be seeing that if everything is working right... Are you making full boost now with the BPV or did it just improve your driveability issues? I think the BPV might be masking other problems that are lurking in there... You've torn it apart for vac leaks, right?
Geez, I'm on a roll today... Good luck tracking it all down, man, and keep us posted...
late :: nick
Your theory on what was happening actually makes sense, but the deceleration valve compensates for the components fighting as you envisioned. It's essentially a BPV for the CIS air metering process that eliminates the stalling of airflow that you described so there should never be that momentary lean condition that you were thinking of. It acts as a throttle controller that allows the engine to dissipate the pressure gradually as you come off the throttle and revs drift down while preserving the previously metered A/F ratio... At least that's how I understand it...
The BPV issue in general is a little different. Check out this pic, clipped from SJM:
<img src="http://www.sjmautotechnik.com/trouble_shooting/ecupic/bypassv.jpg">
As you can see, what the BPV does is to create a feedback loop. Imagine boosted air rushing from the turbo, and then the throttle valve snaps shut. Brick wall. The turbo gets a jolt and spins down more quickly because of the trapped (and increasing) pressure. When the BPV (also called a "diverter" valve for reasons that should be making sense!!) feels vacuum behind the closed throttle, it pulls open and allows the boosted air to take a few laps around the turbo. Throttle opens, BPV snaps shut. Voila. What you get is less turbo lag between shifts and less wear and tear on the turbo.
So, it's hard to imagine that the lack of one would be causing your slugishness / driveability... The stock 10v turbo is so mildly boosted that this problem is almost transparent, so that's why (I guess) Audi thought they could get away without one... Adding one to a properly running car MIGHT be noticeable, but my guess is not by much. No personal BTDT, but think about it -- the only time it's an issue is at WOT making full boost and only for a split second as you shift... That's when you might feel a half second quicker return to full boost. Otherwise, most of your casual driving would be unaffected with the turbo in vacuum (or in a miniscule way at 1.1, 1.2, 1.3 bar...). Watch your boost gauge as you drive around, and you'll see that it doesn't really dip into the boost all that often. Of course, I guess that depends on how heavy your right foot is!!! Mine can be pretty heavy!! LOL... You can definitely tell in more heavily boosted cars, though. Big time.
So, from what you said, you're not hitting 1.4 bar? You should definitely be seeing that if everything is working right... Are you making full boost now with the BPV or did it just improve your driveability issues? I think the BPV might be masking other problems that are lurking in there... You've torn it apart for vac leaks, right?
Geez, I'm on a roll today... Good luck tracking it all down, man, and keep us posted...
late :: nick
03-22-2006, 07:46 PM
#19
no their not hidden at all, right on top of the turbo inlet pretty much.
qpower- just go to the dealership. it's about $30 for one there. you don't want a used one. and twisted5000 is right, you need to do some custom work to make it happen. search this forum, it's been beat to death over the years.