What Diameter is the stock Duramax pipe from the muffler back?
Looking for a cheap solution to my noise problems.
I want to run a 4" pipe off my STS set-up into a 4" resonator then into a 4" tailpipe, want to keep my restriction to a minimum or none at all an muffle some of this ungodly sound!

 

3.5 inches for the piping on the Duramax system.

 

Thanks man, thats what I thought.