Catalytic Converters

gearhead290 · 12-18-2002, 05:38 PM

Shhh, it's not legal! I want my cat. gone! Shhhh! How difficult is it to hollow out my cat.? How much power can I expect to gain, if any?

gearhead290 · 12-18-2002, 08:51 PM

somebody has to know something

Roastin944 · 12-18-2002, 09:38 PM

hey gearhead,
My buddy hollowed his cat in his mazda, it wasnt that hard. We heated up the whole cat until it was glowing red, then sprayed it with a hose and it cracked all the crap inside, then we banged it on the ground and a bunch of stuff came out. What you are suppose to do is hollow it out, then weld a straight through pipe through the cat so the whole shell of the cat isnt actually filling up with exhaust. What he ended up doing is jacking an old cat from behind a muffler shop, cutting off the cuplings on it, sliding in a new pipe all the way through with a little sticking out on each end, welding it in place, taking off the shells, cleaning everything and the shells, tack welding the shells back on and painting it, it looks like a brand new oem cat! You could NEVER tell it goes straight through. Its pretty neat, i will take some pics and post them for you soon, good luck man!

John

AFJuvat · 12-19-2002, 03:26 AM

How hard is it to hollow out your cat? Not hard at all - once you get the cat off...

How much HP? Depends on your car - if your Cat is pretty clogged now, you will see a big difference. You can expect to see a 1 - 3 HP increase by removing the cat.

AFJuvat

Lawrence Coppari · 12-19-2002, 04:00 AM

I heard of someone doing it in situ on his turbo by purchasing a 3 foot steel rod, flattening an end to the shape of a brad point wood bit, then drilling/hammering the honeycomb repeatedly until it all broke up. Running the engine blew all the pieces out.

divezic · divezic's Garage

Check your State legislature to see if there is an emission test requirement in the works. Hollow out your cat now and you may be buying a new one in a few years.

Consider removing the cat, putting it on a shelf and welding a regular exhaust pipe in its place.

Porsche944 · 12-19-2002, 08:42 AM

What you want is called a "Test Pipe."

I live in North Carolina where emissions inspections are mandatory. NC law says that if your car came with a CAT, then you have to have a CAT to pass inspection.

I have a Bursh test pipe and a stock CAT pipe. Each September I remove the test pipe, install the CAT, get the car inspected, remove the CAT, and then reinstall the test pipe.

It sounds like a lot of work, and it was the first time I went through this. I had to use a p-grinder and a cutting wheel to get the exhaust manifold to CAT bolts out. With new stainless steel hardware the job takes about an hour.

The test pipe will give you a few more ponies, the exhaust note will be a tad louder, and some of your low end torque will be missing. Has something to do with having a slightly lower exhaust back pressure.

If you go this route, run the car for about two weeks with the CAT installed BEFORE you get the car inspected. This will give you a chance to make sure the CAT is working properly.

Dougster · 12-19-2002, 10:27 AM

I bought my 86 944 na "catless" or with the testpipe and it is slightly louder then stock and I do think you give up some low end torque vs better hi-RPM power. I think its most noticable when doing it to a Turbo car...Good luck.

rammstein · 12-19-2002, 12:24 PM

Question: If you ran a straight pipe through the cat (so to the naked eye it looked correct), could you pass emissions without it? (I don't live in Cali, I know they are more stringent there).

My cat is loose inside, and it makes a horrible rattling sound from 1800-2000 rpms. Getting rid of it seems the easiest solution.

944jeff · 12-19-2002, 12:54 PM

I have an 86 na that had the rattle. I took off the exhaust pipe and was simply able to dump out a considerable amount of molten metal balls which eliminated the horrible sound. I figured for the small amount of hp you would get removing the cat and the potential I would not like the sound, it just wasn't worth it.

gearhead290 · 12-19-2002, 08:10 PM

I thought about doing a test pipe, but here in SD all a cop can do is a visual inspection and if he sees a cat. hanging down under the car he can't do a thing about it! That's why I want to hallow it. I do think it is pluged, it does make the rattle sound. Has anybody dynoed power gains?

gearhead290 · 12-19-2002, 08:51 PM

Quote:

Originally posted by rammstein
Question: If you ran a straight pipe through the cat (so to the naked eye it looked correct), could you pass emissions without it? (I don't live in Cali, I know they are more stringent there).

no, you cannot pass an emissions test without a catalytic converter! I've also heard that if you get caught without the cat. you can get one h*ll of a ticket.