Took Cats off WOW!

**bc56f100** · 06-27-2005, 08:17 AM

Well I have a 02 avalanche with the 5.3 and wanted to free the exaust up a little but didnt want to hear it (I have had alot of stuff and am just tired of the loud stuff). Well I got a y-pipe from an 04 Tahoe and cut a somewhat flap in the cats and bent the metal back, then beat and scrapped all the inereds out. I then pressure washed inside them to get all the stuff out and bent the metal back over and welded them back up. Used stainless wire of course! So then I took about 45 minutes and pulled my stock y-pipe off and put it up for when I want to put it back on and put the new one on. Well I was kind of scared to see how loud it was going to be when I fired it up, cause I didnt want that but would live with it. Fired it up and damn I couldnt even tell a difference. If you listen very closely you can hear a little difference in the tone when your standing next to the pipe. Other than that it sounds the same at idle. So I took it for a ride to see if it helped any. HOLY CRAP, it gained a but load all over the power band. Down low got very touchy and up top it just keeps pullin unlike it didnt before. And I just dont see the cats being clogged up with only 75,000 and all stock. When taking off and getting on it its like I might be able to hear something but not sure. I know its the exhaust that im hearing but you cant tell its that quiet. This has to be the best thing that I have ever done to a vehicle to get the exact results I was looking for. So basically if you look at the truck it looks like its completly stock underneath. Remember I have the stock muffler under there still. Its just great that nothing was cut on my truck to do this. I will get a tune from my buddy here locally very soon, but so far the check engine light has not come on. I do have a set of O2 sims, but they are for a f-body. Ill let ya know when the light does come on though.

**nikon** · 06-27-2005, 08:20 AM

cool, good too know

**white1** · 06-27-2005, 08:23 AM

I hear you'll see even better gains if you put a pipe in there so the gases dont have to expant and contract back down. Some say that restriction causes a little loss.

**bc56f100** · 06-27-2005, 09:12 AM

Originally Posted by white1

I hear you'll see even better gains if you put a pipe in there so the gases dont have to expant and contract back down. Some say that restriction causes a little loss.

Yea thats what I wanted to do, but just wanted the stock look more. I really am just trying to get a little more power out of it for towing reasons. This along with the electric fans and all the other little free stuff should make it a little better. And of course im sure the gas millage will get better. As if 15 mpg pullin a car on a trailor doing 90 at 4000 isnt good enough!!

**white1** · 06-27-2005, 09:25 AM

I'm thinking of doing the same thing. I have a set of cats at home wiht nothing in them, I'm planning on shoving a pipe thru them so it looks stock, but may just cut mine off and weld a pipe in place not sure yet, but want to do it soon.

**InProgressC1500** · 06-27-2005, 09:46 AM

i'm gonna have to try this with the expedition...it has 4 cats....so surely i'd notice a difference

oh, and i hate you

i don't get that good of mileage without a trailer

**bc56f100** · 06-27-2005, 09:46 AM

Yea that is a good idea. I really didnt want to cut the pipe any. I wanted it to bolt up perfectly and not have to put peices up there and line it all up then tack it and weld it all up. I am just being lazy with this one its my daily driver!! But that would definitly be the way to go.

**bc56f100** · 06-27-2005, 09:49 AM

Originally Posted by InProgressC1500

i'm gonna have to try this with the expedition...it has 4 cats....so surely i'd notice a difference

oh, and i hate you

i don't get that good of mileage without a trailer

Ha yea I think you might see and hear a little more than me with 4 cats.

Yea when we took the cruise to atlanta for the f-body gathering I got better gas millage pullin a car than most of the cars that went!!!

**InProgressC1500** · 06-27-2005, 08:51 PM

Originally Posted by bc56f100

Yea when we took the cruise to atlanta for the f-body gathering I got better gas millage pullin a car than most of the cars that went!!!

**bc56f100** · 06-30-2005, 08:23 AM

Well the check engine light finally came on this morning. Im not sure if its my fuel pump going out (which it is I like to run it low on fuel for some reason), or if having the o2 sensors hooked up with the cats gutted would have an effect on the performance. I did a circle in the road the other day cause I thought I saw a business that I was looking for, but it wasnt it and when I came out of it the truck felt like a pig. I was low on fuel, but not out. Every now and then it will try and come back to the way it was when I took them off. You can tell that something is holding it back cause it kind of surges when on it like it wants to go but wont. Is that possible with having the o2's hooked up and not having o2 sims? Thanks

Billy

**bushluver** · 06-30-2005, 09:14 AM

Sorry if this sounds retarded, first post...

I've heard a lot of horror stories about cutting out the cats...
Burning up the valves
Computer shutting down...

All kinds of things, anyways, are these true?
Or is there a way to bypass the 02 sensors?

Basically can this be done safely without damaging the engine?

TIA

Dallas

**Hammerdown** · 06-30-2005, 05:03 PM

Originally Posted by bushluver

Sorry if this sounds retarded, first post...

I've heard a lot of horror stories about cutting out the cats...
Burning up the valves
Computer shutting down...

All kinds of things, anyways, are these true?
Or is there a way to bypass the 02 sensors?

Basically can this be done safely without damaging the engine?

TIA

Dallas

Welcome to the site!
I think it really depends on the year of the truck (different types of converters, obd I, obd II, etc.) Do a search for gutting cats or similar and there are a bunch related to your questions.