Allright first off I realize this is not the right forum to be posting this but because of the forum rules I am not allowed to post anywhere else. If someone who is an established member would like to steal this and put it in the Turbo Tech Forum, that would be great.
Okay so we all know that the 2g DSM blow off valve are notoriously crappy and hold no boost at all so I decided to get my hands on one and play around with it to see if I could make it hold more boost pressure without leaking. Here's my crappy drawing of a 2g BOV.
A DSM friend of mine gave me one for free to play with so I started to do some bench testing with an air compressor. I made an addapter so that I could hook the bottom port of the wastegate directly to the compressor tank and an extra line with a release valve to use for the top port of the diaphram. I started bench testing it just as it was and found that it was actually leaking at 3 psi of pressure!
Heres why, there is a hole drilled through the center of the valve which allows boost pressure to travel up the valve and inside the wastegate can under the diaphram. Under boost the pressure is equal above and below the diaphram so it relies totally on the spring pressure to hold it shut. With any amount of boost pressure at all the valve is forced open and it leaks.
So why is the hole there? When you let off the throttel manifold vacume sucks all the air out of the top of the wastegate can which combined with the boost pressure under the diaphram forces the valve open and venting the excess boost pressure.
So whats the fix? This is a trick that has been used on the 1g bov's for years, it just takes some creativity to addapt the trick to the 2g's. What you need to do is shut off the supply of boost going to the bottom port of the wastegate can. So just simply find something to plug the hole in the center of the valve. In my case I coated a nail with epoxy and simply stuck it in the hole. Then you need to make a hole to be vent the pressure out of the bottom part of the wastegate can when the valve moves. I drilled a small .100" hole in the can from the outlet port of the wastegate. Make sure you put the valve in in a vise or something to push the valve open to make sure you don't drill into the diaphram when you do it.
After you have done this the wastegate will work as follows
I again bench tested the valve to make sure it works so I filled the air tank with about 20 psi of air and the valve stayed tightly shut. Then I removed the pressure line from the top of the wastegate and the valve instantly vented the entire air tank even without a vacume source. The valve does not have a very good seal so it never seals up compleatly but the amount of leakage is minimal and won't affect performance, you can barely feel it on your hand. Next I started increasing the pressure to see what would happen. I eventually increased the pressure up to 50 psi and the valve still stayed firmly shut. Again I increased the pressure a bit and the valve blew compleatly off the connector from the pressure! So I made one final check to make sure the diaphram was still intact after seing 50+ lbs of pressure and it was. To test it out I put it on my BMW which runs 15 lbs of boost. It never leaked and vented quickly. Becouse I removed the boost source under the diaphram the valve doesn't open quite as easily as before, but it still opens redily at any pressure above 2 psi or so. So if your a cheap ass like me there is a way to make the bov on your 2g capable of holding some boost pressure without throwing it away and getting a new one.
Okay so we all know that the 2g DSM blow off valve are notoriously crappy and hold no boost at all so I decided to get my hands on one and play around with it to see if I could make it hold more boost pressure without leaking. Here's my crappy drawing of a 2g BOV.
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A DSM friend of mine gave me one for free to play with so I started to do some bench testing with an air compressor. I made an addapter so that I could hook the bottom port of the wastegate directly to the compressor tank and an extra line with a release valve to use for the top port of the diaphram. I started bench testing it just as it was and found that it was actually leaking at 3 psi of pressure!
Heres why, there is a hole drilled through the center of the valve which allows boost pressure to travel up the valve and inside the wastegate can under the diaphram. Under boost the pressure is equal above and below the diaphram so it relies totally on the spring pressure to hold it shut. With any amount of boost pressure at all the valve is forced open and it leaks.
You must be logged in to view this image or video.
So why is the hole there? When you let off the throttel manifold vacume sucks all the air out of the top of the wastegate can which combined with the boost pressure under the diaphram forces the valve open and venting the excess boost pressure.
You must be logged in to view this image or video.
So whats the fix? This is a trick that has been used on the 1g bov's for years, it just takes some creativity to addapt the trick to the 2g's. What you need to do is shut off the supply of boost going to the bottom port of the wastegate can. So just simply find something to plug the hole in the center of the valve. In my case I coated a nail with epoxy and simply stuck it in the hole. Then you need to make a hole to be vent the pressure out of the bottom part of the wastegate can when the valve moves. I drilled a small .100" hole in the can from the outlet port of the wastegate. Make sure you put the valve in in a vise or something to push the valve open to make sure you don't drill into the diaphram when you do it.
You must be logged in to view this image or video.
After you have done this the wastegate will work as follows
You must be logged in to view this image or video.
You must be logged in to view this image or video.
I again bench tested the valve to make sure it works so I filled the air tank with about 20 psi of air and the valve stayed tightly shut. Then I removed the pressure line from the top of the wastegate and the valve instantly vented the entire air tank even without a vacume source. The valve does not have a very good seal so it never seals up compleatly but the amount of leakage is minimal and won't affect performance, you can barely feel it on your hand. Next I started increasing the pressure to see what would happen. I eventually increased the pressure up to 50 psi and the valve still stayed firmly shut. Again I increased the pressure a bit and the valve blew compleatly off the connector from the pressure! So I made one final check to make sure the diaphram was still intact after seing 50+ lbs of pressure and it was. To test it out I put it on my BMW which runs 15 lbs of boost. It never leaked and vented quickly. Becouse I removed the boost source under the diaphram the valve doesn't open quite as easily as before, but it still opens redily at any pressure above 2 psi or so. So if your a cheap ass like me there is a way to make the bov on your 2g capable of holding some boost pressure without throwing it away and getting a new one.
