SAAB/Porsche/Bosch BOV Install...
The Purpose:
SAAB and Porsche have one of the cheapest, and most simple BOV replacement parts available, that with only a little modification will replace your very expensive Toyota one. This is not really a performance part. You will not gain horsepower from the change, unless your current one is broken and leaking. It just beats the heck out of the price of the Toyota unit, and works very well. If you need improved evacuation or higher charge capacities, then you're looking to one of the many other aftermarket parts such as the HKS SSQBOV, or the Blitz or the Greddy unit. There are others that I really can't remember right now (you get the idea I hope).
The BOV, as they are commonly referred to, is really a compressor or turbo surge bypass valve. This little device allows the pressurized air an escape route when you lift off the throttle from a boost run. The theory is simple: when the throttle plate closes on the pressurized air mass, it creates a shockwave that travels back through the intake tract until it impacts with the turbine compressor blades. This impact can damage the turbo over time, and does slow or stop the spinning each time it happens, increasing lag. This happens between shifts up, and on deceleration at the end of a run (say at the drag strip). The bypass valves allow the pressure an outlet so the wave does not carry back to the turbo. The result is that the turbine continues to spin quickly, minimizing lag on the next step on the throttle, and additionally saves the precious blades and bearings/bushings inside the turbo additional wear and tear.
The first question then is whether yours works or not. Remember this is not really a performance increasing mod, but rather a cheap alternative that may help a very little to vent that shockwave, or hold slightly more pressure than the stocker. No sense doing this unless yours is bad. First, remove the factory one and try to blow through it (clean it up a bit first...rather dirty after being under the hood a while to be putting to your lips). If you can, you are in the market for a new BOV, and this modification may be for you. If not, you are likely fine and do not need this. As I said, this is not a performance enhancement part, but a cheap, very high quality replacement. These Bosch made parts will not hold a lot of pressure, and are well suited to stock or slightly modified cars. Rumor has it the Porsche unit can take 16PSI of boost, but I have not had that verified. For high boost applications, you should have hard-pipes on your intake and then get the HKS or something.
Parts:
For the SAAB it is the compressor bypass valve from a 1996 9000 Turbo. They cannot cross reference the Bosch part number, so you have to look to see that you have the correct one when they give it to you. It is molded into the side of the part, Bosch part #0 280 142 103
The Porsche part according to the SOGI tech tip is Bosch part # 0 280 142 108. Apparently it uses steel internals vs. the SAAB plastic. Never having seen the Porsche, I again cannot verify this. Porsche calls it an Air Cut-off Valve, and lists it as Porsche part # 993.110.337.50. Presumably, this comes from the 993 turbo model. Nice car!
1 - 1 1/2 feet of 1" radiator hose
approximately 1 foot of 5mm vacuum hose
The Install:
This one is pretty simple. Remove the old BOV from the car, as well as both hoses. Don't toss the hoses just yet. The new BOV has ~1" fittings, where the old one had about 5/8". You can get adapter hoses as recommended at the SOGI site, or for a really inexpensive job (or in a panic. I had cut my hoses off only to find out that the Toyota and SAAB sizes are different!) you can make the adapter hoses. You need a 1" radiator hose, and about a foot should do. You can fit this to the BOV after measuring the lengths you need from the 3000 pipe to the BOV and the BOV to the accordion hose. Now, you are going to cut off the old BOV hoses to make the adaptors. Cut them only long enough to cover the metal fittings they came off of, and clean the cut pieces well. Now, insert them in the ends of the 1" hose connected to the BOV, using a little epoxy to glue them in place. These ends you have after the initial cut are going to be about an inch long and should be completely inserted. I went so far as to taper and chamfer mine as well to smooth the air flowing areas out as well as possible (Yes I am anal...just ask Larry Anderson). After making sure they fit, put them back on the metal fittings they came off of and clamp them down. Now, hook the vacuum hose from the BOV to the metal line the old one was attached to and Voila, you are finished.
NOTES:
There are 2 things to note after the install is done. First, the vacuum line fitting on the BOV is 5mm, and the Toyota one was 6mm. I used a 6mm - 5mm male to male vacuum hose adapter to allow me to use commercially available red silicone hose. In my case, I couldn't find 5mm red silicone, so this had to do! It is also less of a squeeze to fit the correct 6mm on at the metal line end of the BOV vacuum system, while the fit on the BOV itself remains perfect. 6mm all the way along requires you to use a tiny hose clamp on the BOV, which is a PITA to try to fit in that small space and still look clean.
The second note is that the BOV makes a new sound. It hoots like an owl as you cross from vacuum to boost. If you hold it hovering around 0 PSI (mmHg), it sounds like a miniature fog horn! This is normal. Some say the new Bosch ones and the Porsche ones do not hoot, but I suspect they do. The 90 degree bend in the valve makes rushing air cross it like blowing over a coke bottle. You get a sound because of the shape, not because of the parts used in each. The Porsche one is said to whistle however, and would do so for the same reason!