gutting cat

[jaws]

is this a good idea? I know some people do it... but are there any real benefits to it?

[martiniac]

Here's a great description of why not to gut a Cat:

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.

[Turpro]

A performance catco straight thru cat is only 50 bucks.

[jumpncrash]

Al Gore says no to cat gutting

just get a high flow cat, that way u can stay legal, and be good for the environment

[Mazda_Powered]

please don't gut or remove your cat...its not worth it. no benefits...get a high flow one.

JACK.

[Kitty]

gutting a cat when a test pipe is just too expensive o.O

[MazKid]

Take your cat off and turn it in for scrap. Use that money to buy a new high-flow cat. Screw the environment, but gutting a cat will make the car sound like piss. How do I know? The stock cat on my Protege grenaded and clogged the exhaust...my dad, a Mazda tech, took the cat off and gutted it to prevent the other elements from clogging the exhaust too. It sounded trashy...actually, not very bad all things considered, but just not good. I then attempted to make a test-pipe, that was mediocre. Eventually took the car to to Midas and got a 2.5" highflow cat put on to go with the catback.

[jaws]

nice. thanks for the help! that first huge description of why not to gut the cats I read on automotive forums. Might as well not **** up emissions, be illegal and have no performance upgrade. thanks!

[militarypolice2]

oops

[wheresthericego]

I recently read a article in a major import magazine. I don't remember the name it might be modified mag or import tuner but they dyno tested a vehicle with a normal cat, the same vehicle with a highflow cat, and then the same vehicle again with a test pipe. To throw a number out there we'll say the stock dyno was 155. The dyno with a highflow cat was 159 and you get a staggering 160 hp with a test pipe. I don't remember the exact numbers but The fact of the matter is that the high flow cat gave 4 hp and a test pipe gave 5 only the highflow cat is LEGAL. It does not matter what state you live in, gutting a cat on a vehicle that was originally equipped is illegal and in some states/countries it is a very severe crime.

[bandman659]

Grassroots Motorsports also did catalyst tests last month with a Miata, which I believe they are preparing as a nationally-competitive Spec Miata racer. Basically, the car still met Texas' (very lax) tailpipe emissions requirements even without the cat, but the dyno showed approx. 2 hp gain over stock for the test pipe and for all of the high-flow cats they tested. The high-flow cats also produced much lower emissions and a couple of them were pretty dang cheap.

So there's really no reason to go catless unless you're making some pretty good power and aren't NA. With a high-flow, you'll make the same power and not be a polluting douchebag.

Disclaimer: I work in environmental engineering (mostly soil/groundwater remediation, but some air quality stuff too), so my opinion of emissions modzzzz may be a little biased.

[jaws]

well that's good to put some numbers to the comparison. There isn't an aftermarket test pipe for the bg though... unless you make one of course. I know magnaflow has a high flow cat and catco too. I think i'm going to get one of those, or if I do the DOHC conversion someday I will put the headers and the downpipe and the high flow cat plus corksport's catback. that would be a nice setup.

[Kitty]

I recently read a article in a major import magazine. I don't remember the name it might be modified mag or import tuner but they dyno tested a vehicle with a normal cat, the same vehicle with a highflow cat, and then the same vehicle again with a test pipe. To throw a number out there we'll say the stock dyno was 155. The dyno with a highflow cat was 159 and you get a staggering 160 hp with a test pipe. I don't remember the exact numbers but The fact of the matter is that the high flow cat gave 4 hp and a test pipe gave 5 only the highflow cat is LEGAL. It does not matter what state you live in, gutting a cat on a vehicle that was originally equipped is illegal and in some states/countries it is a very severe crime.

Its a federal crime. In every state.

[wheresthericego]

Its a federal crime. In every state.

I thought so, I just didn't wanna make a claim not being 100% sure

[militarypolice2]

whats the punishment if you cought with a gutted cat?