Would a 3X3 fernco coupling work as a Smooth Rubber Bellow ?

 

Ain't much flex to them things. They're meant for a butt type (end to end) connection with Sch. 40 Cast Iron or PVC pipe.

What are you trying to connect with this fernco?

 

MAF to TB, I have seen it done on an LS1 but I am wondering if it will work on a V6 ? If not what would I have to do to make it work? Because it a cheap mod and I am probably looking at 5 potential HP or at least better airflow

 

If it's going to be a solid mount, and not ment to isolate vibrations, body mounted part to engine, you should be all right.
And a little hint here, while most Ferncos are for Schd 40 (thick wall) pipe, they're also made for copper tube, thin wall pvc and orangeburg and combinations of the different types of pipe. So you should be able to find a good tight fit for what you're doing.

Good luck