If you go to the web site testemonials and search for diesel you will see there are no results. I would have to guess they designed this for gas engines where there tends to be a lot of backpressure. My 2 cents.
I had a leftover stock system and I cut 2 of the elbow's out of it and welded them together. I saw a pre-bent piece on ebay that gave me the idea.Where did you get the pipe to delete your muffler on your stock exhaust. This is what I want to do till I get $$$ for a complete 4" system.