Well i received my new Cat-Back system today, and have been kicking around the idea of gutting/hollowing out my Cats, was wondering if anyone else have done this mod, i understand you get better mpg, better acceleration, and best of all a killer sound..

Before you say it, yes i know its illegal, only if you get caught..

My plan is to drop the Cats, use a cut off wheel to open them up, gut the innards, my MIG welder, to close em up, then a nice coat of Header VHT exhaust paint, silver of course to match my brand new SS exhaust system...no one would be the wiser..

Yes, i also know about the CEL, there are many ways around that..

As far as the environment, i drive a Hummer H2, enough said...

I forgot to mention, the innards of the Cat, is very valuable, can easily sell to a salvage yard...

 

Heres the exhaust that will be fed by the gutted Cats, a Stainless Steel AFe Mach Force Exhaust...

 

You don't have emissions in your state? I have to take mine next month....again....

 

I wouldn't do it. You are going to have the check engine light on. Sometimes a gutted cat can make weird sounds on deceleration, it will also hurt your resale.
If you really want it off I would cut it off and weld a pipe in place and then you can reinstall if you sell or your state incorporates emission testing.
You will not see performance gains unless your cat is plugged.

 

We don't have emissions testing as a State wide requirement. It's per parish (we have parishes, not counties). Luckily, where I am, it's a non issue.

I lived in Colorado for 6 months & I felt like I was under a communist regime in terms of the emissions testing & cost.

 

Not true, their are many ways around CEL, just look at youtube. ..

First i ever heard of "weird" sounds from Cat

I never plan on sellingit, doesn't apply

Not true, you will see better performance, mpg and sound, why you ask, no back pressure. ..

 

Yes we have emissions inspection in NJ

But they only use tailpipe probe on 96 or older cars, or trucks..

Anything newer, they use the ODB connection under dash, if no codes are found, you pass, i have done a clearing of codes on my wifes durango, it has a evap leak, so everytime i go to inspection, i wipe codes prior to leaving house, and i breeze through inspection everytime. ...

 

You're lucky. AZ is probably the worst state for emissions. Mine has actually been put on the sniffer for an idle test (no AWD capabilities at the testing centers) along with the OBD test. Always passes, barely budges the needles on the sniffer test. Truck is 10 years old now and my tags next months are still $240....

 

a quote from another website
Do not "gut" the cats. There are several reasons not to do so. Especially if the engine is still normally aspirated. They are as follows:

The major one being that the current generation of catalyst elements are not very restrictive at all. In fact, they actually work like a tuned collector on normally aspirated engine. As the exhaust gases pass through them, they act like a check valve for exhaust flow. As the exhaust valve closes, momentum causes the gases to continue to travel through the exhaust system. This is plenty of energy to pass through the cats. This causes a vacuum to build up between the exhaust valves and the catalytic converter. The energy required to pull the gases back through the element can't build fast enough to work before the next exhaust valve opens. When that next exhaust valve opens, it is opening to a vacuum environment which helps to PULL the gases out of the cylinder due to what is called "scavenging effect". This translates into more power as the piston now does not have to do all the work to evacuate the cylinder of spent combustion gases.

Second, if you were to remove them, you would definitely want to use a cat removal pipe. The chamber left after you would "gut" the cat is actually worse at losing energy than a catalytic element (understand I mean element designs after around 1990). This is because as the gases enter the empty chamber, exhaust velocity slows down. As it then regroups to enter back into the exhaust piping, it does not have the energy it did before, therefore it "stacks", causing backpressure. This backpressure now works against the flow of spent gases out of the cylinder when the exhaust valve opens, causing the piston to do all the work. Now, energy is being wasted for gas removal that could otherwise be used to turn the crankshaft.

My recommendation would be to leave the cats alone and concentrate of every other part of the airflow system. After all else is done, come back to them, and if not using a high flow catalytic converter, then use a cat-delete pipe.

 

Another reason I'm glad I moved back home, lol.
I don't recall the price, but tags were expensive in CO, but I'm glad I don't deal w/ that crap. We only have inspection stickers here. $20 gets you 2 years. I'm only fighting with them now about window tint. I'm on the boarder line & they don't give me the benefit of the doubt. I've never had a cop pull me over & people roll around with tint so dark, you can't see in the vehicle. I'm not sure how they are getting stickers.