What's What On the Exhaust??
 

I picked up a used CAT and DPF, but need to know which is which. Is the CAT before or after the DPF??

:alone:

the cat on a cummins is in the down pipe. the 2 tanks are dpf and nox filter

Awful small CAT. :humm:

So needless to say, but will anyway, I got a used DPF and Nox filter.

Be worth the crap to install the Nox filter anyway, and not worry about it being plugged up?? Which leads me to another question: which one is the DPF, the long can or short can??

:alone2:

I pretty sure its the long one

The only place a cat, DPF and NOx filter have value is in the garbage. Unless your engine is programmed to keep them clean all they'll do is plug up in a few weeks and kill the engine with backpressure.