New exhaust and Bad Mileage

[JVolpe]

DBeardslee



I concur. I was discussing this very issue this afternoon. The concenses of the discussion was that 5" exahaust should not hurt performance or MPG from 4" in any way. Straight piped from turbo down pipe back bigger than the outlet should all be the same. After that it is more personal preference or driving habits that come into play. Of course this is just my SOTP type response.

 

[Sled Dog]

At that speed, with your rig, its not to bad.

 

[Scrappy]

no its not. with a 9 cm exhaust housing, it doesn't matter what is behind the turbo. The turbo is so restrictive, that anything down pipe doesn't matter. . I've run 4 and 5 inch set ups with absolutely no changes in mpg or peak torque on the dyno.

It DOES matter. the surface area in the 5" is so great that it cools the exhaust too much and the air slows down. at that point the air has to be pushed out the end of the pipe, and that takes a little power from the engine to do. my truck dyno'ed @ 250 with my exhaust and intake mods, but I did the exhaust once and won't have to change it again with my plans for the future(twins). and that 9cm3 housing is restrictive but the wastegate doesn't go thru there so it helps slightly.

 

[DBeardslee]

Explain that to my bumper that changes colors like your heating it with a tourch :-laf

 

[Scrappy]

Explain that to my bumper that changes colors like your heating it with a tourch :-laf

at low rpm's is when the effect is the worst, as the rpm's climb, the effect lessens, you aren't going to see 1300 deg. @ 1500 rpms but might see it @3000 rpms.