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Discussion Starter #1
i have an 85 w123 300d turbo diesel. There are two vacuum relays? near the brake booster on the firewall one is on the left closer to the engine, one is on the right. What does the one on the left side do? It has been disconnected by the previous owner. there are three ports one on top with a vent cap one on the front and one on the bottom. I belive the one on the front went into a three way tee that is located where all the other rubber threeway tees are. i don't know wherer the one on the bottom went to. there are numbers on the side of the relay that i can describe if that would help. thanks
 

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If what you're referring to is the highlighted item in the pic, that is the turbo overboost switchover valve. As you can see it has been bypassed on that car, my CD. The SD is hooked up. I've been told by an MB mechanic, bypassing is not a problem. Four of five 123's (turbos) I've owned, were bypassed. IF STOCK set up, no problem.
 

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mine looks similar. the line on my car goes straight from a banjo fitting on what looks like the back of the intake manifold next to the atf dipstick. then it goes to the pressure regulator? square box.

Also do now if the overboost switch valve bleeds air from the wastgate to increase pressure? if so hooking it up could make the car faster?
 

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That is the ALDA, so pressure regulator is about right, an altitude adjustment type affair.
I'm not sure about your second question, but all this valve does is, I think, to open the waste gate if dangerous boost conditions occur. You will not be gaining power. I believe you would need to adjust fuel pressure and perhaps other things. I am familiar with stock set ups only. There is a web site, Schuman Automotive /Forums - Powered by vBulletin in there is an area about super turbos.
 

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