i am considering putting a high flow on my truck, its got the 5.9. right now im straight pipe from cat back to a y pipe then duals out the back bumper. my question is, if i put a high flow in would it make it run differently (leaner or richer)? would it hurt anything?

 

It'll be a bit louder, and maybe a little better throttle response, but, that's it.

 

Unless you live in a place where they do inspections I wouldn't worry about a high flow cat, just straight pipe it.

 

Magnaflow makes a direct fit one.
https://www.magnaflow.com/products/2...ytic-converter

 

ive just heard from people about how the 5.9’s need back pressure or it could possibly hurt the bottom end

 

No engine needs back pressure, that's a myth, however exhaust scavenging is important.

 

so i could cut the cat completely out or put a high flow and it wont hurt anything?

 

Would have to get O2 non foulers

 

Yeah, if you completely remove the cat entirely, you will need to do something with the rear O2, the PCM uses that to monitor cat efficiency... if there is no cat, then it ain't real efficient, and the PCM will whine. Easy to work around though.

 

If you don't want a code just pull the rear O2 sensor out and tie it up somewhere.