boost bypass valve?
03-08-2002, 08:33 PM
#16
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It appears there is a little confusion about the function of the stock boost bypass valve. We did some bench testing of the stock bypass valve and found a couple of notible things.
First off, it will definitely hold more than 15 pounds of boost, infact we tested it at over 25 pounds and there was no leakage, but, there is a condition to that test. The vaccum/boost control like has to have the same pressure in it to assure that the bypass valve works correctly.
When we had 25 pound of pressure in the 1" inlet and the same pressure in the control line, everyting worked as it should, but if you disconnected the control line, the valve immediately started leaking badly.
This bypass valve operates somewhat like the wastegate in the respect that the pressure under the diaphram (as the boost builds up) pushes on the seal until it lifts it enought to start leaking. The exhaust backpressure in the wastegate forces the wastegate open and the boost level starts to drop.As long there is control pressure, it will hold lots of boost.
One possibility that could cause these erratic pressures is that the line or pressure connections on the control line to the bypass valve are leaking, maybe only under higher than stock boost levels. Underhood temps could effect the rubber "t" connections and just a small leak could let the bypass valve blead off boost.
There are many functions that are controlled by these tiny pressure lines, leaks in other areas such as rising rate fuel regulators could cause huge problems. A simple pressure test of the intake system would indicate whether this could be the cause.
We feel that the reason the stock bypass valve is so prone to failure it the higher boost pressures. When you lift off the throttle suddenly and the throttle body closes, the turbo is still spinning and takes a split second to start to slow down. That boost pressure spike is what the bypass valve is intended to releive. The diaphram inside these things is rather delicate and at stock boost levels and volume they can take the abuse, but at 15,18, 20 pounds, it is hitting this valve pretty hard and it doesn't take long to rupture the diaphram. Going to a rebuildable unit would help on the wallet over the long run but if you don't have enough blow-off capacity things are still going to tear inside the unit.
The only solution in that situation is to either add a second factory bypass valve or a larger one capable of handling the higher volume of larger turbo or higher boost pressures.
A simple way to see if your stock valve is enough is to do a little street test. Preferably with a passenger in the car to read the gauge for you while your driving, simply lay into the boost and run the car hard say in 4th gear. When you are at full boost and everything is flying by rather quickly, side step the gas pedal. Make sure your passenger is watching the boost gauge closely, if he sees a sudden spike of boost, especially if it goes a couple pounds higher, you don't have enough blow-off. This condition doesn't do the turbo any good either.
Good luck,
Mike at LR
First off, it will definitely hold more than 15 pounds of boost, infact we tested it at over 25 pounds and there was no leakage, but, there is a condition to that test. The vaccum/boost control like has to have the same pressure in it to assure that the bypass valve works correctly.
When we had 25 pound of pressure in the 1" inlet and the same pressure in the control line, everyting worked as it should, but if you disconnected the control line, the valve immediately started leaking badly.
This bypass valve operates somewhat like the wastegate in the respect that the pressure under the diaphram (as the boost builds up) pushes on the seal until it lifts it enought to start leaking. The exhaust backpressure in the wastegate forces the wastegate open and the boost level starts to drop.As long there is control pressure, it will hold lots of boost.
One possibility that could cause these erratic pressures is that the line or pressure connections on the control line to the bypass valve are leaking, maybe only under higher than stock boost levels. Underhood temps could effect the rubber "t" connections and just a small leak could let the bypass valve blead off boost.
There are many functions that are controlled by these tiny pressure lines, leaks in other areas such as rising rate fuel regulators could cause huge problems. A simple pressure test of the intake system would indicate whether this could be the cause.
We feel that the reason the stock bypass valve is so prone to failure it the higher boost pressures. When you lift off the throttle suddenly and the throttle body closes, the turbo is still spinning and takes a split second to start to slow down. That boost pressure spike is what the bypass valve is intended to releive. The diaphram inside these things is rather delicate and at stock boost levels and volume they can take the abuse, but at 15,18, 20 pounds, it is hitting this valve pretty hard and it doesn't take long to rupture the diaphram. Going to a rebuildable unit would help on the wallet over the long run but if you don't have enough blow-off capacity things are still going to tear inside the unit.
The only solution in that situation is to either add a second factory bypass valve or a larger one capable of handling the higher volume of larger turbo or higher boost pressures.
A simple way to see if your stock valve is enough is to do a little street test. Preferably with a passenger in the car to read the gauge for you while your driving, simply lay into the boost and run the car hard say in 4th gear. When you are at full boost and everything is flying by rather quickly, side step the gas pedal. Make sure your passenger is watching the boost gauge closely, if he sees a sudden spike of boost, especially if it goes a couple pounds higher, you don't have enough blow-off. This condition doesn't do the turbo any good either.
Good luck,
Mike at LR
03-09-2002, 04:45 AM
#18
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where could i pick up one of these forge valves?
the site listed doesn't have anything for porsche apparantly.
checked paragon and pelican, only found what looks like an OEM
please email me, dannyzumwalt@mac.com
thanks
the site listed doesn't have anything for porsche apparantly.
checked paragon and pelican, only found what looks like an OEM
please email me, dannyzumwalt@mac.com
thanks
03-09-2002, 03:15 PM
#19
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Danny951, you can order from <a href="http://www.stratmosphere.com/forge_valves.htm" target="_blank">Stratmosphere</a>. Even though the site is Audi based, the Forge valves are a direct replacement for the 951 OEM valve (Bosch). You can either use the 006 or the closer to stock size 007.
03-11-2002, 12:38 PM
#21
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I just installed the Forge 007P on my Turbo S in place of the stock Bosch unit. The installation was a snap, took all of 5 minutes. Works like a dream - the boost comes on earlier, stronger, smoother and longer. Looks good, too. I have now ordered another one for my other Porsche - a 911 Turbo 3.6.
03-13-2002, 12:12 AM
#23
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Tecart, I don't think you can buy direct. Stratmosphere is the US ditributor. Forge is in Europe. If you go into the website, Stratmosphere,
they have the different ordering options.
they have the different ordering options.
03-13-2002, 05:58 PM
#24
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I just ordered the 007P for my car to see if I notice any difference but in talking with the saleman he said I would want the track (yellow) spring for the track which keeps the turbo spinning inbetween shifts better so I ordered that too for a extra $20. My question is why has this yellow spring not been mentioned in any earlier posts?
03-13-2002, 10:35 PM
#25
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Is there anyway I can have the stock BOV modified so I can hear the air vent when I change gears? I like the way that sounds. My cousin did it on his 93 rx7. It sounds great! Thanks. Is there a baffle that muffles the sound?
03-14-2002, 10:03 PM
#26
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do you guys notice any sound with the forge unit? A friend of mine as well has a really nice "chssh" sound in between shifts from his BOV and I think I want that too.. if the forge doesn't do it, what are some other BOV's that are easy to swap out of the 951 that will do that? I don't guess the 993 valve will.
03-14-2002, 10:23 PM
#27
Nordschleife Master
The BOV's that make that cool woosh sound vent to the atmosphere instead of back to the intake. Some report idling/running issues...others not. I'd look for more info on the subject.
Little tidbit...we have a CBV cause it vents back to the intake.
a BOV is basically a CBV that vents to the atmosphere.
Little tidbit...we have a CBV cause it vents back to the intake.
a BOV is basically a CBV that vents to the atmosphere.
03-15-2002, 09:00 PM
#28
Race Director
The problem with venting to the atmosphere is two-fold. First it doesn't keep your turbo spooled up as much as redirecting the air back around. Second this air has already been measured by the AFM/MAF sensor. And the DME will inject the proper amount of fuel. If you dump this air out to the atmosphere, you'll end up with a too-rich mixture. On shifts with dropping RPM, an improper mixture can cause stumbling or a completely dying idle.
03-17-2002, 03:47 AM
#30
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[quote]Originally posted by Danno:
<strong>The problem with venting to the atmosphere is two-fold. First it doesn't keep your turbo spooled up as much as redirecting the air back around. Second this air has already been measured by the AFM/MAF sensor. And the DME will inject the proper amount of fuel. If you dump this air out to the atmosphere, you'll end up with a too-rich mixture. On shifts with dropping RPM, an improper mixture can cause stumbling or a completely dying idle.</strong><hr></blockquote>
ah, i see. so, is the forge a BOV or a CBV? They do have a cool sound clip of a wrx with some kind of forge bov and it does make the vent to atmosphere noise.. does the 007p and 006p not do that even though they still call it a BOV?
what's the deal?... i think i'll just go with the 993 unit from paragon.. $33 or something.. not bad.. cause mine is broke and when i shift the boost gauges immediatly drops to 0.4 bar and when i push the accell, it shoots back up and kind of wobbles.. i think it'll be much better for my turbo if it doesn't have to halt and go so much.
-so- is the forge unit a true BOV to atmosphere or not?
<strong>The problem with venting to the atmosphere is two-fold. First it doesn't keep your turbo spooled up as much as redirecting the air back around. Second this air has already been measured by the AFM/MAF sensor. And the DME will inject the proper amount of fuel. If you dump this air out to the atmosphere, you'll end up with a too-rich mixture. On shifts with dropping RPM, an improper mixture can cause stumbling or a completely dying idle.</strong><hr></blockquote>
ah, i see. so, is the forge a BOV or a CBV? They do have a cool sound clip of a wrx with some kind of forge bov and it does make the vent to atmosphere noise.. does the 007p and 006p not do that even though they still call it a BOV?
what's the deal?... i think i'll just go with the 993 unit from paragon.. $33 or something.. not bad.. cause mine is broke and when i shift the boost gauges immediatly drops to 0.4 bar and when i push the accell, it shoots back up and kind of wobbles.. i think it'll be much better for my turbo if it doesn't have to halt and go so much.
-so- is the forge unit a true BOV to atmosphere or not?