Hi all im new to the site and i figured id jump right in. I have a 2007 monte carlo SS with the 5.3 and my little brother has an 06 monte with the 3.5. Im hoping to sell mine soon (and get a camaro ) but anyways both our cars have cold air intakes and bolt on exhaust kits. My question is, beyond the fact that it illegal, would we gain anything by cutting off our cats and running straight pipe? We've been told that we'll see worse gas mileage? but it seems as if the cars would breath better and not having a cat would free up more power? Please give us yall's thoughts.. also my little brother's car has the magnaflow exhaust and it sounds good for a v6 but what sound affects would he have without a cat.. Would it be ricer like?

thanks alot guys

 

I'm not sure about any HP gains but no CAT increases air flow so your engine can breathe better. Having no CAT is illegal but I think you can get them hollowed out or something. I'd wait for other knowledgeable members to help you out.

 

the only thing that i could think of causing worse milage after you lop off the cats is the O2 sensors not liking the extra emmissions, and they might make the car run lean / rich?
im pretty sure you could bypass / deleate the O2 sensors without much pain and suffering if they become a problem

 

semi answered but would like more thoughts on it..

 

i jnst cut off the cat on my 03 monte with bolt on cat back exhaust its seems to me like i got a little horse power increase and my gas mileage is right about the same. depending on where the cat is you can hollow it out but mine was a pain so i just cut it out and welded stright pipe in there.

 

hp gain will be minimal...it will be louder but id have to say if your doing anything get your self a high flow cat that way u'll get the little gain and still be legal

 

Why would it change how the car runs? The pcm only uses the front O2 sensor for fueling adjustments, the rear is simply there to make sure the cat functioning.

 

really???? well, that just shows how much i know about cats, lol. almost all the ones ive had were hollowed out, but they were on older cars w/ primative electronics. heck, what you said clears up some questions of my own, lol.

 

cool thanks alot guys. My brothers gonna do it but I think im enjoying my last week with my monte as I have a buyer coming from new jersey to pick it up on friday.