The first problem if you unplug your valve, you are left with a ~1 inch hole in your intake line, just in front of your compressor. As you can imagine, this will confuse the heck out of your ECU.
The solution?
I am apparently an idiot, because I want more noise. I want more induction noise. I miss the amazing whistle I used to get when my exhaust snapped off just before the cataltyic converter. I want my hooter valve to wake up the neighbors.
This is the story of the little hooter that could (maybe. We aren't nearly finished yet)
This all started with an innocent post on the forums at Saab Central, asking about an atmospheric BOV. A few questions, and a lot of inept scheming, later, I decided to act rashly and without half the information I needed.
The stock BOV on my car is a recirculating design. When triggered to open by the manifold vacuum, the valve opens, allowing pressure from just before the throttle body to vent (through an odd hose) back into the intake line, just before the compressor.
I don't have a picture of the stock setup, so you'll have to use your imagination.
There are two problems with switching your Saab from recirculating to atmospheric.
The first problem if you unplug your valve, you are left with a ~1 inch hole in your intake line, just in front of your compressor. As you can imagine, this will confuse the heck out of your ECU.
The solution?
This was abuse of whatever I could find at the finest. In case you are wondering, the black thingie is a Master Cylinder Gasket.
Note that I don't suggest that you actually use this for something safety critical, for example, your brakes. There were little cracks in both of them, all the way through. I'm pretty sure that means they will leak.
At least now you know why I RTVd a quarter into the center. It was mostly to plug that leak, and partly to add rigidity. I didn't really want that flimsy gasket breaking loose and getting sucked into my compressor vanes (which seems really unlikely anyway).
Here are more views of the thingie.
Bottom(huge)
Side (blurry)(huge)
Top (if you thought the last one was blurry...)(huge)
With that hole blocked off, you can put things back together, the way you found them. One exception: the valve that used to be plugged into that port will be left loose.
Which leg of the valve do you plug into the hose and which do you leave loose? Doesn't matter, at least not for this.
What does it all look like in the car? Not incredibly impressive, I must admit.
Now, the Saab has a nice atmospheric boost dump. It also has a nasty vacuum leak. This is problem number two in case you were wondering when I'd get around to that one.
How bad is this vacuum leak exactly? I put my thumb over it and it wasn't like it was trying to suck my skin off, so I guess it could be worse. On the other hand, the car no longer idles when cold and has a tendency to stall if you let off the gas in neutral, but once warmed up can actually idle if you let it down easy.
What else does this mod do?
Well, there is a dramatic change in throttle response. When you hit the gas, the car kicks more than it used to, at least according to my asscelerimiter. And just as it goes up harder, it comes down harder. When you let off the gas, it bogs down much more severely than it used to.
Stay tuned for part two, In Search of a Check Valve
I suspect I can find a check valve to correct the leak much more easily than I can find a proper atmospheric dump valve, so I'm going to try that to see what it does.
I took a little trip to Home Depot and came out with the following items:
| CHECK VALVE | 9.49 | for a sump pump |
| STL CLAMP | ordinary hose clamps | |
| 2 @ 0.98 | 1.96 | |
| 3/4X2GALNIPL | 0.67 | galvanized pipe, 3/4" ID, 2" long |
| VINYL TUBE | 1.69 | hope it can take the heat |
| GLAV.BUSH | 2.47 | 1.5" end cap with a 3/4" threaded hole |
Vinyl tube is clamped onto the outlet of the BOV. The 2" pipe is threaded into the other end of the tube. The other end of the pipe is threaded into the end cap. The end cap is threaded into the check valve. Everything gets clamped down.
Results?
Well, it now makes some noise, but not really a lot. I think the volume between the throttle body and the atmosphere is just too big, and the check valve is friggin' huge.
The car now idles wonderfully. However, it still tends to stall if you don't let it down easy.
Stay tuned for part two point five, Can I tweak the anti-stall dashpot?
Dashpot adjusted, sorta. Mostly I just turned it in some and prayed for the best. On my first test drive, it stayed high (over 1200 RPMs) most of the time, unless I was sitting at a light. After a while it would gradually drop under 1000 if it sat for a while.
It did stall once, so I adjusted it some more. High idle seemed a little better, didn't stall even once, but it looked like it was about to once or twice. I'll probably leave it like this for a bit, then adjust it again.
I also moved it. Instead of floating by the air box, it now hangs down under the bumper.
I was able to finally tuck it down under the intercooler deflector.
More pics:
