Bypass valve worth it? [Archive] - SaabCentral Forums

: Bypass valve worth it?

21st July 2002, 11:52 PM
On my 1996 9000 Aero, is it worth the 40-50 bucks "U.S." for the Bypass valve? Also, did your car handel any differtentlyThanks for the help. This would be the first thing i have changed on the car since i got it 2 weeks ago.

22nd July 2002, 03:00 AM
Well it means that your revs won't keep rising up when you take your foot off the gas.

22nd July 2002, 11:17 AM
Sorry for the stupid question, but is that a good thing or a bad thing. I am still new to cars at only 17 years old. Thanks.

22nd July 2002, 04:52 PM
Some people find that annoying because right as they shift the revs start dropping. With a bypass valve I think the boost generated gets recirculated or something so it doesn't just get lost whereas with a blowoff valve the pressure just gets dumped out.

22nd July 2002, 04:56 PM
I retro fitted a dump valve to my old 900 8valve turbo.
It made the car feel more responsive and faster when changing gear.
It also helps protect the turbo when running high levels of boost.
Hope this helps.

22nd July 2002, 05:11 PM
Do you want it to dump to atmosphere or back into the inlet before the turbo? If it dumps to atmosphere you'll get a Ptschh noise when you lift off when the cars on boost and a slightly faster drop it revs when lifting off. If it dumps back before the turbo you'll get less rev drop and no ptschh. It depends if you want it fast and furious style or not :wink:.

I've got to say theres some advantage to living in the US I wish I could have insured a 9000 Aero when I was 17. I've just insured my 900 T16 (set me back over a grand) and its just a bare shell with half the suspension and a steering rack at the moment.

Cheers all

23rd July 2002, 12:00 AM
Thanks for all the help, but now i have another question. I was going to get the bypass valve from a saab dealer, but the one from the viggen, i can get it cheaper then on-line, and on-lien they stated it was the one from the viggen. Is this correct?, and also does the bypass i get depend if its drops into the atmospher or before the turbo, or can i test it out both ways and see which i like better. Right now the bypass i have on the car makes a swoosh sound when i am accelerating hard and then let off the gas, but i think that this is the one that came on the aero. Thanks for all yoru help again. Oh, the only reason i have an 1996 aero at 17, is that we got a super super super deal on it.

23rd July 2002, 02:28 AM
man i just wanna kill you....
thats a nice first car....

All saab 9000 trubo's come with bypass/dump/blow off/whatever valves....
The stockone is the recirculation type....
Yes some sort of valve should be used as it helps to problong turbo bearing life and boost response on gear changed....

Nothing other than a more defined sound and maybe looks will be gained by changing it (unless the stock one is rooted)....

On a 9000 you can run an atmospheric dump on the valve if you want as it is MAP sensored... No such luxury on a classic 900...

Janne Selinummi
23rd July 2002, 07:41 AM
Correct me if I'm wrong, but wasn't it so, that on Trionic 5 you can use an atmospheric dump valve, whereas in the Trionic 7 you can't? I just heard this somewhere, supposedly these systems have different sensoring method or something...

23rd July 2002, 09:44 AM
So what your basically telling me is that the bypass valve that is being sold is the same on that i already have on my car? nd it wont really help out in performance?

23rd July 2002, 12:41 PM
Janne is correct the T5 uses a MAP sensor and the T7 uses an MAF sensor (called AMM in saabs), the blowoff valve will allow unmeasured/unfiltered air to enter the engine, creating a difference between the actual amount of air in the engine and the amount of air the AMM signal represents.

Janne Selinummi
23rd July 2002, 02:52 PM
There are differences between dump valves, and a bigger unit is needed when you have more boost to dump. Also, the valve had to be more durable, since with higher boost levels, there's going to be more air that has to pass through the valve. If your engine is standard or close to standard, a more efficient dump valve isn't needed; but if you need a new valve anyway then I'd say it's wise to get a unit that's more durable than the OE part.
The difference between recirculating and atmospheric valves is the sound they make, but also the efficiency of the design; in very high-boost applications of racing cars and the most powerful tuned turbo cars, you'll see atmospheric valves mostly, and that's down to the fact that the atmospheric valves can dump more excess air faster than the recirculating ones.

24th July 2002, 12:15 AM
Hey.. i was planning on getting a new recirculating valve for my '96 900se turbo coupe, but it sounds like the performance difference is minimal, and the atmospheric valves are easier on the turbo.. so i think im gonna go for the Pshhh sound, hehe :razz:. My only question is if using an atmospheric valve in my model is a good idea? if anyone could tell me about any complications ide really appreciate it, thx.

Janne Selinummi
24th July 2002, 06:16 AM
Which version of the Trionic management system does your car have? If the system has an air mass meter, then the atmoshpheric valve isn't a good idea, but if it's MAP-sensored, then it'll work fine.

24th July 2002, 02:25 PM
How do i know what i have in the car? I am really new to this. Thanks again.

Janne Selinummi
24th July 2002, 07:43 PM
It should read on the control unit, and probably it's in the owner's manual too. And definetely, it's in a repair manual, such as a Haynes workshop book - IMO, a good repair guide is an essential item in Saab ownership just as it is with every other car.

25th July 2002, 01:05 AM
<TABLE BORDER=0 ALIGN=CENTER WIDTH=85%><TR><TD><font size=-1>Quote:</font><HR size=1 color=black></TD></TR><TR><TD><FONT SIZE=-1><BLOCKQUOTE>
On 2002-07-23 17:41, conradFL wrote:
the blowoff valve will allow unmeasured/unfiltered air to enter the engine, creating a difference between the actual amount of air in the engine and the amount of air the AMM signal represents.

</BLOCKQUOTE></FONT></TD></TR><TR><TD><HR size=1 color=black></TD></TR></TABLE>

Actually an atmospheric BOV will let air escape that has already been metred... Hence giving extra fuel resulting in super richness... Though this is only with Air Flow Metred cars ( MAF, AMM)...

I think you should be alright on your 96 model... I know my mums 96 9000 is MAP sensored and a non-recirculating valve can be fitted.

If anybody is hoping for a performance gain from a new valve... Forget it unless your existing one is faulty....

25th July 2002, 01:55 AM
yes,'re right. engine will run rich and your CE light will come on. to tell if you have T5 is easy all 900/9-3's 94-99 (except 99 viggen) have the T5.

28th July 2002, 07:31 PM
contrary to popular belief dump valves do nothing to make your car faster. if you are running race level boost pressures an atmospheric dump valve is the way to go. if not, just stick with the oem stuff, its cheaper and works just as well. a viggen bypass valve(the one the dealer is trying to sell you) would be where id put my money. you can get 20psi boost and it will still work effectively.