vertical exhausts

[Frank Lee]

In all likelihood there is more total pipe length.

[Ryland]

If he needed new exhaust anyway then right there could be the improvement, if I remember right the exhaust on those trucks is not very straight so he could have ended up with fewer bends even tho it makes a 90 degree bend, it jogs up and over the rear axle and around the fuel tank I believe.

[CanadaLT]

Originally Posted by euromodder

Did he maybe cut down the back pressure as well while doing so ?
Remove the catalyst, silencer or stuff like that ?

Nope, no other changes but i asked again today and his improved number are more like 6%. Still not hugely significant but still something.
When building it up, the diameter was not increased but there was one less bend (it was a minor one so i don't see it being a big help)