So I'm contemplating gutting the cats on my 02 2500HD with the 8.1L. What are the affects of this?? I've got about 100,000 miles on it, and it seems to me it is having a little bit of a hard time breathing at times. My mileage is never any better than about 9, so can it worsen if I do this? I didn't think there were any O2 sensors after the cats on an 8.1L, but my shoulder is broke so I can't look right now. And also, I had a rear mount turbo on this truck for a short time, and had a lot of trouble making boost in 1st and 2nd gear. I plan on putting it back on and i figured the cats may have been part of the low boost issue. I'm up for all pros and cons, thanks.

Leave it. You will hate it with it off. Everything will go down including power.

Leave it. You will hate it with it off. Everything will go down including power.

Very true! But for a rear mount cats need to come off. They tend to flake off and go through the turbo and will damage it.
I would suggest when you put the turbo back on, do like I did. I y-ed the exhaust at the front where the driver side crosses over. Then run a single 3" to the turbo. I even used the stock piping that I took off the truck. I did run a stainless flowmaster before the turbo to keep noise down. Then header wrap it from the manifolds to the turbo to keep heat in.

DONT DO IT!!! i did. HUGE MISTAKE. my 496 is N/A but i lost mileage and power when i removed mine. wish i hadnt

Remove the cats when you make the switch to long-tube headers. :thumb:

Remove the cats when you make the switch to long-tube headers. :thumb:
as soon as i win the lotto):h

why would you remove the cats with long tubes?

why would you remove the cats with long tubes?

Because they are restrictive and unnecessary

i thought the 496 was designed to work with cats for backpressure?

the 8.1L cats are HUGE....I can't see them being a restriction on anything less than 600RWHP. I replaced mine with a set of high flow metalic spun CATs from Magnaflow when I installed the stainless works Long tubes and they seem to be working great. Dont think I would delete them unless you are going rear mount or making insane amounts of RWHP.

so whippled why did you go with aftermarket CATS instead of factory? better flow and less restrictive? and would the magnaflow cats work good on a N/A 496?