I'm useing a stock brand new bov on my mod 951 it seems to work well but i have heared that the stock bov bleads boost under higher pressure. Has anybody experianced this and was the upgrade an eye opener?

 

Jimbo1111, There are two problems with the stock bypass valve. The main one is that the diaphram tears all the time the other is that it leaks under higher boost. Some people go with the 993 valve but a better route is to go with the Saab valve. It is a bosch unit,looks exactly the same and the internals are as good as the 993 but the real benefit is the much stiffer spring so that the leak problem you refered to is no longer a problem. This valve is more than enough for 951's that dont have crazy horsepower and is about 40$. I posted this earlier but put in the wrong price. The bosch number is 0-280-142-110 and as far as noticing a difference,it is not drastic but possibly enough to merrit a change to the Saab valve. Another neat thing is the using the 2 bypass valves. I have seen John Milledge using this and John Anderson. I asked John Anderson how it worked (see the current maf post) and he said it worked out pretty good. You should check out the picture the current post.

 

Is the spring in the saab valve stiff enough to be used as a blow off valve rather than a recirc.?
Ahmet

 

It should also be mentioned, that Porsche installed the blowoff valve in wrong position. The way it is installed, the pressure works against the whole diaphram, not only against the closing area. The 993 valve was strengthened at that area - but that is useless in stock position.

I would recommend to flip the blowoff valve. It still fits perfectly and works better at high pressure -,and the diaphram will live much longer.

 

"but i have heared that the stock bov bleads boost under higher pressure."

I don't see how it could because boost is fed into the top of the diaphragm at the same time as the bottom (through the side port from intercooler). This would result in a force of zero on the diaphragm from boost regardless of the level. Then you also have vaccum from the J-pipe below pulling down on the bottom port. Then there is additional closing force on it from the spring...

 

[quote]Originally posted by Danno:
I don't see how it could because boost is fed into the top of the diaphragm at the same time as the bottom (through the side port from intercooler). This would result in a force of zero on the diaphragm from boost regardless of the level. Then you also have vaccum from the J-pipe below pulling down on the bottom port. Then there is additional closing force on it from the spring...[/QB]<hr></blockquote>

You're right Danno, but there's a significant delay for the boost fed into the top. The stock lines are too small to give imediate response. That causes problems in part-throttle situations at high rpms. The problem get worse with higher boost. To compensate this it helps to use a stiffer spring and/or bigger boost lines.

 

Is the opening large enough to exaust the pressure of a garrett turbo?

 

[quote]Originally posted by jimbo1111:
<strong>Is the opening large enough to exaust the pressure of a garrett turbo?</strong><hr></blockquote>

The Bosch OEM blowoff valves in all their different versions for vauxhall, audi, vw, saab,... are designed for "soft-turbo" engines. I would not use them over 1 bar (psi ???) and not in a high-flow system with big turbos and free exhaust-lines.
Here's a comparsion with a "real" blowoff valve:


I think it is better to have one good valve than two weak valves in parallel...

 

That looks like a mighty valve but for most applications the Saab valve should be good enough. It has a much stiffer spring in it compared to the one in the 993. Friends with 340+ rwhp have used this valve on the 951 and another friend of mine has a modded Audi S4 running 21psi with out problems with this valve and the modified S4's are notorious for blowing their bypass valves. Sure, there are better valves but unless you have major turbo, high boost and crazy RWHP on the 951 you dont need more than the Saab valve. This is my opinion from my experience, but yes transaxle the stock valve is made for the weaker turbo cars.

 

white 944 turbo,
Do you know where a good place is to get that sabb blow off valve? thanks for the assistance.

 

Hello? I understand you're saying that the Saab valve is all mighty, can you tell me if the spring in it is strong enough to not vent at idle if it's hooked up as a blow off valve rather than the stock (recirculating) configuration?
Ahmet

 

Ahmet, the valve I called mighty was the one that transaxle showed. The Saab valve can hardly be called mighty but it is a better alternative to the 993 valve. You can put your finger in the valve and see how stiff the spring is compared to the 993 spring and its known to be a much stiffer spring. I did not know this until recently but apparently alot of people know this. As far as being strong enough to vent into atmosphere I am not sure. But if you wanted to do this I think you would have to modify the pipe going to the turbo intake. I know alot of the Japanese cars do this but Im not sure if it would benefit the mildly modified 951. Again, I mention this Saab valve not because it is a great valve but if your going to buy a 993 valve you should spend the same money to get a bosch valve that is better.

 

Johne, if your interested in the Saab valve Im sure you can pick it up anywhere you can get bosch parts but the place I can recommend is <a href="http://www.webparts@europroducts.net" target="_blank">www.webparts@europroducts.net</a> and the bosch number is 0-280-142-110.

 

I have a 993 valve, but I'd like to have 2 bovs. One to atmosphere one to recirculate. I have all the plumbing necessary (I tried this w/two stock valves, and the car didn't run that well due to the huge vacuum leak I created. Looking into this I realize true BOVs used much stiffer springs). Anyway, I wouldn't mind trying the saab valve at all, could you check to see if it'd be open at idle for me?
Thanks
Ahmet

 

I have a 993 TT blow off valve installed and I run 25+psi. What is the advantage of changing to one of the previously mentioned bov's?
Paul