Removing the Cats

John Robinson · 06-13-06, 07:45 PM

Today I stopped buy a muffler shop to check on the price of flowmaster mufflers for my 93. The owner of the shop put my car on the lift and noticed I had the resonator removed. He was convinced that I should retain the stock mufflers and remove the cats. He said I would get better gas milage and performance. He also stated that he could hear a whisper in the right side that told him my cat on that side was plugging up. My question is has anybody done anything like this and what were the results. I mainly want a fuller sound from the car. The muffler shop owner said I would probably get that sound with the cats removed. He gave me a price of $80.00 to do the job. He also said I would not get any codes because the O2 sensors were ahead of the cats. I need advice from someone that has done something like this to their car.

Vettefan87 · 06-13-06, 09:10 PM

Hmm...I thought on all the LT1 engine cars they had O2's before and after the cats, but I could be wrong. He is right though you will get a better sound and an increase in HP, but I am not sure about the gas mileage increase. I am suprised a guy at a muffler shop said he would do that, because it is illegal.

What was he going to put in place of the cats?

Ted Krempa · 06-13-06, 10:33 PM

John, ask the muffler guy if he will agree to replace your computer and all the emissions stuff that blows up after he cuts the cats off. Oh, and ask about the fines from your DMV if they inspect your car.

Doing what he suggests is a stupid idea. It kills me to read the lengths people on here sometimes go to circumvent the millions of dollars of research that GM has spent in designing our cars to operate properly, legally and efficiently. Performance mods are one thing, and the hallmark of the American 'hotrodder', but ideas like that are just plain dumb.

There are 100+ posts on the forum from guys who have legally upgraded exhausts. Check 'em out !!!

Good luck, Ted

toptechx6 · 06-14-06, 04:18 AM

Your 93 LT1 only has "upsteam" O2 sensors so cat removal may have no negative consequences in regard to setting codes or damaging the PCM with one exception, it could impact EGR operation since it uses a negative back pressure style valve. I do agree with Ted one hundred percent that environmental damage and possible legal problems will be maximized for minimal performance gain. You and the muffler shop are begging for trouble, do it the right way.

John Robinson · 06-14-06, 06:59 AM

Ok if I don't do the cats can I get any gain from changing the mufflers and which would give me the best sound and quit cab at cruise. Cant afford Corsa but have long dreams about the Corsa system. At this point all I want is a more macho sound from the exhaust on acceleration.

geogolf · 06-14-06, 07:09 AM

john not sure if you have pre cats like my 90 but this is what I did removed pre-cats altogeather and ran just one high flow main cat with borlas mufflers not to loud but sound lot better than stock geo.

JEFNLSA · 06-14-06, 10:31 AM

One other inexpensive option is to remove the mufflers and replace w/ straight pipe (a la muffler elims). You can have them weld the stock tips back on. Shouldn't cost you more than $100 & the Vettes that I've heard w/ that setup sound great.

c4cruiser · 06-14-06, 11:05 AM

The removal of properly operating cats on a car that meets federal emission standards by a shop can result in a $10,000 fine in a federal court. No self-respecting shop should even suggest doing this. Even replacing a good cat with another (like a high-flow version) is technically a violation of federal law and can result in a fine.

The later C4 cats should not cause a lot of reduction in exhaust noise compare to the earlier C4 designs that used pre-cats and a main cat. If you look at them, they are really only about a foot long and actually flow very well.

Flowmasters can have a lot of resonance to them depending on the model selected. The Series 40 and the American Thunder models are probably the loudest and may cause a lot of interior resonance. Without the factory resonator, these mufflers will make the car loud!

BTW, most all of the C4 cat back systems include some sort of resonator to control interior noise.

WhalePirot · 07-16-06, 08:41 PM

If your CAT is plugged as he stated, you likely will see an improvement in performance, but given his other advice, I'd have doubts about his "whisper".

I ran my previous engine with and w/o the CAT; finding very little difference in performance 'feel'; hardly worth the risk. I expect the newer CATs flow better that the old single. I did, however, feel improvement with Flowmasters replacing the stockers.

Resonance of the Flows may result from the large, flat radiating surface, but I don't mind much.

*89x2* · 07-16-06, 08:43 PM

Quote:

Originally Posted by Vettefan87

Hmm...I thought on all the LT1 engine cars they had O2's before and after the cats, but I could be wrong. He is right though you will get a better sound and an increase in HP, but I am not sure about the gas mileage increase. I am suprised a guy at a muffler shop said he would do that, because it is illegal.

What was he going to put in place of the cats?

OBD II cars have multiple o2 sensors (before and after cats)

OBD I cars did not

Vettefan87 · 07-16-06, 10:21 PM

Quote:

Originally Posted by *89x2*

OBD II cars have multiple o2 sensors (before and after cats)

OBD I cars did not

Ah ok