You would have to show me the facts on a dyno. I have two units and have advanced the mods one at a time. The 4" no cat no muffler is quieter, more powerful and sounds better than the modified 3 1/2 system. I also have had my own truck fleet for 30 years and have never seen a diesel that responds to backpressure. The valve timing is much different from a gasser. The faster you can let the gases expand away from the turbo the better. Reduces EGT's and quickens spool up. Like any engine though, the more you crank up the power, the more exhaust you need to get rid of.