This is a late update, but the ridges of the turbo-to-exhaust coupler filled up with carbon in short order and the faint whistle shortly went away. I've since rebuilt the turbo and reinstalled the tube that goes inside the coupler. So, I don't recommend removing the tube inside.

When I ran the engine with the air cleaner off after installing the turbo, I could not hear any turbo noise when revving the engine, so I don't think that anything before the turbo is going to help with making the whistle heard. I also don't want to put any holes in the exhaust.

It's interesting that my previous 300SD had such a loud turbo whistle. It's possible it had a leak somewhere after the turbo that was letting out the sound. I noticed it had some strange large round metal gasket at the housing that I haven't seen on other Mercedes turbos.

At some point I may delete the muffler and resonator. I have a hole in the muffler, anyway. Like I said, I don't want the engine to be louder, I just like turbos when they spool up, like on every other brand of diesel. I tightened up the wastegate spring until I was out of threads, but the most boost I am getting is 12 psi, barely above stock specifications.

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DON'T MESS WITH MY MERCEDES!


1967 W110 Universal Wagon, Euro, Turbo Diesel, Tail Fins, 4 Speed Manual Column Shift, A/C
1980 W116 300SD Turbo Diesel, DB479 Walnut Brown, Sunroof, Highly Optioned, 350,000+ Miles