My first M109A3

[sporkius]

For the C turbo, it's gonna be hard to tell. You'll need a side shot. The C turbo is thinner than the D.

Side shot of the engine?

 

[2027Deuce]

If you look at a C turbo, it loos like a konk shell, like it would whistle with air going through it. The D turbo has a wider air passage so the air doesn't get forced through a smaller opening and then whistle. Do a search, I think someone may have posted pics at one time. When you start whatever truck you are looking at, let it warm up then give it a medium rev up, when it spools back down you'll know if its a whistler. Good luck.