Saabscene Saab Forum - Saab Technical Information Resource banner

Atmospheric Dump Valves

6K views 45 replies 14 participants last post by  brent 
#1 ·
I've been looking at Forge's website. Specifically, I have been looking at the dump valves. I want to get one for the Viggen. Not because I think it will make it faster, or because it's somehow better performance wise. But sometimes I like to go out at night and scare the local Import Owners with some healthy boost noise. But even with the open air filter element (which has since been replaced with a stock air filter) there was very little in the way of boost noise. Wouldn't run it around town normally, but this valve is "supposed" to work on Mass/airflow sensor cars. As it is TWIN piston and does not allow air in at idle:

http://www.forgemotorsport.co.uk/products....product=FMDV004

Looking at the other atmospheric valves, they say specifically that they are NOT compatible with mass airflow cars, but the two ram twin piston ones seem to be. Just curious if anyone has comments on it. They do have one with a filter on it. Which I thought was kind of neat.
 
#2 ·
The Forge twin piston design does indeed work with mass metred cars, as does the Bailey DV26 Evo (also twin piston).

I ran a Bailey Evo dump valve for many months without problems until deciding to replace it with a Forge recirc unit as I was getting tired of the noise.
 
#3 ·
Apart from the possibility of leakage which gives idle problems, I understood that the other reason atmo dump valves don't work with AMM cars is that at the point you dump the pressure, the engine will overfuel (possibly to the point of flooding/stalling) as the ECU is adding enough fuel for the air which it has metered but rather than going in to the cylinders, has now been lost...
 
#5 ·
Figure at the VERY WORST I get one REALLY GOOD WHOOSH out of it before it stutters and dies.
If it doesn't work after that I wasted about $140 but heck ... might be worth it for that one good whoosh. Sides I think it may very well work. An AMM car typically disregards the airflow sensor for a split second when shifting. Because when the air is being dumped the throttle is closed and when the throttle is closed the airflow gets pretty unpredictable, and the airflow sensor isn't really sensing anyway. Do wanna try it though. Now if I can just scrounge up $140 ... being in debt kind of sucks.
 
#6 ·
Originally posted by Adrian W:
[qb]Figure at the VERY WORST I get one REALLY GOOD WHOOSH out of it before it stutters and dies.                  
     :fawlty:      If it doesn't work after that I wasted about $140 but heck ... might be worth it for that one good whoosh.  Sides I think it may very well work.  An AMM car typically disregards the airflow sensor for a split second when shifting.  Because when the air is being dumped the throttle is closed and when the throttle is closed the airflow gets pretty unpredictable, and the airflow sensor isn't really sensing anyway.  Do wanna try it though.  Now if I can just scrounge up $140 ... being in debt kind of sucks.    
 [/qb][/b]
Could you not just make a deal with the seller that you will try it and if it works you will then buy it? This can be hard to arrange if purchaced via internet.
 
#14 ·
I found this at an other saab forum:

I have a 2002 Viggen and I just installed an atmospheric dump valve. I can not be too sure if there is any performance increase but the sound that is produced is awsome. The combination of the Opti-Flow intake the dump valve and a freer flowing exhaust really make this SAAB sound great.

But I do have a problem. After long stints of hard acceleration the check engine light comes on. If I take it easy the light doesn't come on. While the light is on the car does not run any different.

Any Ideas?


He person did not mention what type of BOV he used.
 
#16 ·
I ordered a Bailey dump valve today for the 99. Spent an hour or so chatting to Bailey, as I wanted as little "whoosh" as possible. Eventually we decided to go with the atmospheric twin piston type, but with the stronger spring (used for boost pressures of up to 2 bar. This stronger spring slows the opening rate, and therefore the gas release rate slightly. Means the effectiveness of the valve is reduced a little, but hopefully not too much
 
#17 ·
Here is some more info about the case I posted above.

------------------------
I had already purchased the BOV by the time I found this thread. I purchased the unit from Forge Motor Sport. The car ran fine with the CEL on. But it was annoying to look at. Restating the car did not reset it. And I drove with it on for a couple days to try the multiple start method. I may not have done it long enough though be cause it did not work. I had to disconnect the battery to reset it.

I called Forge in FL about the CEL but the guy I talked to had no idea that the BOV would not work on my car. They did offer to exchange the unit for the recirculating one though.

Vigge, was unable to get the code from the ECU, sorry.
----------------

So no luck with the forge unit.
 
#18 ·
Well ... no luck if you don't like the CEL on. I only want it to make some noise at the track when I finally get some finances back here. Might save me showing everyone the turbo on the car when they wonder why a lil 4 cyllinder Saab (why does this thread force ellipses on that?) was so fast. I don't wanna run it around town anyway. Most of the time the stock BPV is more than adequate at releiving boost pressure. Just not good enough at making noise.
 
#19 ·
Well, if you are looking for the noise but don't want the CEL and perhaps stumbling or such from different fueling because of the atmospheric dump valve, there is an option. Get a BSR Optiflow intake. You'll hear the dump valve dump, just the same as an atmospheric one, and also hear the tubo spool up more and the intake whoosh as you get on and stay with the go fast pedal. The Optiflow comes with a barrier to combat uner hood heat and needs just a little bit of work to seal it off from the rest of the engine bay.

You can see pics of it at www.bsrab.se .
 
#21 ·
I tried the open air filter. I was a little dissapointed though. It was somewhat loud inside, but outside not very loud at all. Really I only want the BOV for the occasional trip up to LACR to scare off all the slow cars. Last time I went the fastest car to race me ran a 15.9.
Several ran 16's and 17's. Maybe the BOV would encourage a little more competition. I doubt I'd want to hear any kind of loud whoosh on a regular basis anyway. Also, the T7 system can probably compensate for the air leaking out. I was reading with one of my friends that most cars throw the "overcompensating" code when they have less than 25% possible compensation remaining. Not that I reccomend using a BOV for extended periods, but it's likely since it doesn't immediately throw the code (as earlier testament showed it was when driven hard for a while), it likely still has compensated and is just warning that it's being forced near it's limits of doing so. Still, if it throws a code I wouldn't drive it every day like that. Definetly not good for the motor.
 
#22 ·
If you are only after intimidation power of the sound, why even bother. I think you should let the performance of your car do the talking. IMHO, trying to pose and threat with a noise is kind of a ricey thing to do, isn't it?

I say you should let your track performances do your advertising for you.

Also, I'm not entirely sure, but I remember some t7 owners on tSN mentioning stumbling and bogging after shifts, sometimes, with a atmospheric valve. That surely will not help your drag racing performance.
 
#23 ·
True. I am concerned and if it stumbled or hesitated as a result I would probably ask them if I could exchange for a better BPV instead, or a refund. As for letting the runs do the talking, I did make 10 passes last time. The last one was against the slowest person yet, 17.6.
The only people who paid much mind to the car were in the crowd. They may have cheered for the "underdog" when I ran the Evo, but they weren't racing. Could be a while before the Viggen makes it back to the track anyway as I'm trying to make funds for a dyno run. Last Friday would have been a really good day if I'd had the money. Only 68 degrees F, and rather high humidity for this pseudo desert. Hopefully the weather continues along that trend again soon. Anyway ... Atmo dump valve = ricey? Naaaah ... most of the ricers have theirs set all wrong and they make that "WHEw whew whew" noise. A nice whoosh = rally. 'least that's how I see it. Of course the valve comes AFTER the dyno run. So won't be too soon. Keep on Saabin'
 
#24 ·
I was just thinking about the whole running rich between gears as a result of the BOV conversion. Most really high performance turbo cars richen the mixture between gears. Typically because (this is what I've been told most frequently) when the throttle closes the air doesn't stop going to each cyllinder at exactly the same time. This can briefly cause a cyllinder or two to run lean. Under high boost even running lean for a second can be hazzardous so they tune it very rich to keep this from happening. That's supposed to be why you often see high performance turbo cars shooting flames out the exhaust between gears. Well aside from the ones that cut spark rather than close the throttle. Of course most high performance cars don't last long, so I don't think it'd be a good idea to do this to a stock Saab. But I did think it was interesting. It at least gave me enough confidence to be willing to try the BOV for short stints. I know that over the course of a few minutes it won't blow up my rather pricey Saab motor.

 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top