Just working on the donor car (85 300D) to get everything running nice before it comes out and goes on the stand to get pretty. About to do glow plugs and ream (starts a little rough but clears in 15-30 seconds) and rebuild/clean the turbo (spools pretty slowly and smokes juuuuuust a hair with very little blowby). I'll save the valve guide seals for when the motor is on the stand.

So my question is this: what the hell is this huge dingus thing on the compressor housing on my KKK K26 turbo? Some kind of compensator or something? Google has been less than helpful, as has been my personal knowledge of turbos (I'm a piston aircraft mechanic so I'm pretty familiar).

I'm asking about the round housing with the little rubber hose poking out.