As per subject line- I have been trying to sort out an appropriate air cleaner to turbo intake duct which reduces from the the 75mm at the cleaner, to 60mm at the compressor housing. The dodgy arrangement I had been using was pulled recently and while there, I thought I'd give the compressor wheel a bit of a look-see.

I was a bit surprised at the resistance to rotation on the cold motor. It won't spin freely as it were. It will turn on the finger but won't free spin (run on). I've checked the oil pressure and water, and these are fine. There is no end float play, and no upward/downward play at the shaft- but it wont free wheel. I'm wondering how much is too much rotational resistance? I checked on another turbo (a GT25) sitting on a dead OM605.960 Benz four valve motor, and resistance on this is somewhat less than on the TB2518. The GT25 is worn out- and demonstrates endfloat and shaft play without wheel-fouling the compressor housing.

Road behaviour of the 4BD1T is somewhat sluggish until it is fully warmed up...it whistles on boost cold or hot. This is one of the reasons that I pulled the intake duct arrangement because I thought it was allowing ingress of supply air thereby creating the whistling quality (turns out it wasn't) but now I suspect that exhaust gasses are trying to rotate the turbine that is offering rotational resistance. Once the engine is fully warmed, there is a mild surge when the turbine is spooling but absolutely nothing to write home about. These things have a large compressor housing and no wastegate. They are underwhelming...

Thoughts?

I have an HE221w Holset spare that i was saving for a w460 G Wagon re-power. This is said to be an ideal replacement for the 4BD!T (Dougal's threads here and on 4Bt Swaps) but plumbing and down pipe mods are a PITA- then there's the adaptor flange from T3 down to T2...not a days fiddling to have sorted but the payoff might be worth the effort. the TB2518 is a bit pathetic to be honest.

Cheers
Steu