hey guys have a 2003 Gmc Sierra with the 5.3l its a 1500 4x4, it has a bully dog tuner, and one flowmaster super 40 1 in 2 out, it sounds great but just not loud enough. i have been thinking about cutting out the cats to make it louder, and run more free flowing, i have a couple of friends that have said that in doing this it will mess with the computer, i have other friends that say it will run better. let me know what you think on this
thanks guys
Ryan

 

it is illegal, but im not stopping you, nor am i a cop. it will give you more power, however i fear that whatever power you gain will be complicated by what it does to the engine. it will no longer have a correct reading in the exhaust, and throw an engine code. it may cause a LOSS of power and the engine will run a tad richer... i would advise against it on a newer model truck such as yours... if you want as loud as possible with your cats on, cut everything off all the way up to the converters, and just get a shop to bend and weld straight pipe all the way back and weld on some tips and you will have a toneless, obnoxious true dual exhaust system.. however it will be loud and turn heads, though maybe not for good reasons..

 

I have a 02 silverado 5.3L that i cut the cats on a year ago. Your truck will be alot louder and u will have more power at high RPMs but you will lose alot of bottom end power, so if you tow alot I wouldnt do it. I ended up putting cats back in mine and ran straight pipes from the cats back along with shorty headers and it came out sounding pretty good and running alot better. If you do cut em off make sure you keep them because if you decide to put them back on they can get pretty expensive. I bought mine at NAPA for just over $400.

 

It will throw a code but not make it run richer. The downstream O2 sensors only let the computer know if they are working or not. A tune can delete those sensors. I have on mine. These motors need back pressure to run good. Free flowing will make it run good in top end. If you cam out the motor then free flowing would be great. But these motors dont put out much exhaust to run free flowing. I noticed on mine its great on top end, but not much bottom end, which I am camming my motor out anyways. Louder doesnt always mean faster.

 

thank you ruffneck for correcting me! (not sarcastic) im glad when people set me straight sometime lol.. its just what i had been told and assumed for years, but glad someone gave me a right answer as well!

 

Hey no problem. I also used to assume that before I learned what it really does. I have a feeling though the future will have changes made to these loops we find to work around.