stock bypass valve info & links for replacements [Archive] - SaabCentral Forums

: stock bypass valve info & links for replacements

23rd December 2002, 08:48 PM
Hi, I'm new to this forum. I have a '99 9'3 S w/ a 5 speed manual tranmission. I discovered on my own a very big drawback of the stock bypass valve. I know many of you already know this, but for those that do not, here is a really good reason to replace it with a higher quality unit. I hve had several turbo car before thi, so I know a good bit about how they work and what uually goes wrong. Here is my hypothesis. While under light boost at partial throttle, I can notice an odd moaning noise coming from the 3" hole in my air box. This sounds odd, but it has really simple solution. The factory bypass valve generally stays open at vacuum and draws air in through the little pipe that connects it to the lower part of the airbox. This is why it draws this air in through the airbox even though T5 models have no mass air flow sensor. While building slight boost, it simply forces its way through the bypass valve and right back into the intake after the airbox. By doing this, it never reaches the intake manifold, which means there will never be a positive pressure signal to close the bypass valve at low boost. What all this means is this: the first few pounds of boost ae basically worthless, there is alot of responsiveness that is lost during this time. Basically, replacing your blowoff vlave will do more than make noise and look pretty, it will wwiden your power band considerably. I just received my new Turbosmart blow off valve tonight. I will let you guys know how I like it as soon as I install it. Here are a couple of sites where you can find good parts besides the SAAB part sites.

Hope this makes sense or helps someone out, Justin.

4th January 2003, 12:40 AM
Interesting. Anything to get this thing rolling faster from a standstill is welcome. Let us know if it changes anything for you!

26th January 2003, 03:49 PM
If you experience problems with the stock valve
on newer (Trionic7) cars with a recurculating
bypass valve I can recommend to upgrade to the
slightly larger unit from the Mitsubishi EVO.

It has 35mm connections instead of the stock 25mm
but that is easliy fixed with straight reducers.

Will hold for higher boost, and gives a slightly
more aggressive sound (when combined with an open
air kit that is).

8th February 2003, 09:26 PM
Hey, it has been a while since I replaced my bypass valve w/ a Turbosmart type 2 vee port model. The odd noise coming fom my airbox is gone entirely. The transition into boost comes on much more smoothly due to the fact that the first onset of boost is actually producing power. I also added a JR drop in air filter nd this comes highly reccomended as well. Thanks for rading this! If you have any questions that I could answer, feel free to ask, thanks, Justin.

Ben Young
9th February 2003, 10:32 PM
Try going to this site: The Forge site:

erp reccomends here, i do as do many others.