Hi all,this section is very interesting and I spent allot of time reading your posts.

I have a Mercedes w201 2.5 diesel 1989 model.It's Europe version because I'm from Malta.The engine has only 68000 KM on the clock.The engine is in very good condition starts first time no black smoke and it's strong for a 2.5d.

Now I am planning to add a turbo,I don't need to much more power but what I'm looking is to add some more torque.

If I add a turbo how much psi can the engine take without harming the inner parts?

Hi,

maybe you can get an idea of "allowed psi" out of the STT threads.
Without having the correct number I would say max. 0.6 bar.
But the STT kit was for 617 engines with iron heads. The "new" stuff is weaker and you risk to damage the engine.
For adding just a little more torque my opinion is that adding a turbo (you might also need the turbo IP) is way too much trouble and $.
The fastest solution is to swap the engine (2.5 turbo).
The cheapest is to turn up the IP (done on the bench by someone who knows what to do).

Tom