Removing 2 Cats

apats77 · Mar 20, 2012

Feel free to tell me this is a terrible idea if it is.

I live in MA. I want to free up my exhaust if I remove one of the cats (each side) will my car still pass emissions? Which ones should be removed? Any one with more info I would appreciate it.

wmburns · Mar 20, 2012

The Mustang has two cats for a reason. The first is called a "light off" cat. The 2nd is a normal cat.

The purpose of the "light off" cat is to burn off excessive hydro-carbons in the exhaust. As a result, the cat has been designed to handle the higher heat. If the Light off cat is removed, then the excessive hydro-carbons will now be burned in the normal cat. This will raise the temperature and greatly reduce it's service life.

If the regular cat is removed, likely the light off cat will not be enough to meet smog requirements.

A well designed high flow cat is likely a better idea.

Bob Hughes · Mar 20, 2012

I removed the rear cats still have all O2 sensors hooked up and passed NJ inspection. Never had a check engine light.

apats77 · Mar 20, 2012

Thanks wmburns, would i be incorrect by thinking the car has 6 cats total? what am i seeing?

03_TrueBlue_GT · Mar 20, 2012

I believe the California 1996-1998 V8 Mustangs came with six cats total... Two preheater cats and then 4 regular ones...

Someone might correct me about the California thing or if its the whole country, but I have heard about them having 6 total..

Bob Hughes · Mar 20, 2012

If I remember right my 98GT had 6 cats I hollowed all of them. My 03GT has 4, I removed the back 2.

apats77 · Mar 20, 2012

So in my case what would be recommended? remove last one or last two?

ryan281 · Mar 20, 2012

Call the place that you would go to get your emissions done and ask if they still use the sniffer on your exaust pipe because you want to do dumps. If he says no just buy MIL eliminators from american muscle and you can run no cats just put them on the second 02 sensors and you wont have a check engine light when they plug in to ur computer for ur emissions. I live in illinois and thats exactly what i did and i just passed with no cats last week

wmburns · Mar 21, 2012

apats77 said:
Thanks wmburns, would i be incorrect by thinking the car has 6 cats total? what am i seeing?

I'm fairly sure that the stock 96-04 Mustang GT/V8 has (4) cats. Two on each side. Light off cat is first followed by a regular cat. It's been a long time since I last worked on my 96.

I'm positive that my 2000 and 2003 has (4) cats.

A muffler or resonator does not count as a cat.

If it still doesn't make sense, best to post pictures of your car. Possible that it's not stock.

I'm not sure it makes any difference. Either you are or you are not concerned about passing any SMOG test.

If you are not concerned, then do what every you want.

If you are concerned, then making any modifications away from stock is always a gamble. It may pass today, but what about tomorrow? What about changes in the law? Would you be pissed if the cats did not last the life of the car?

apats77 · Mar 21, 2012

I've now heard that what i think is a Cat might actually be a resonator? Its right at the bend after the headers and before the first cat.

SteedaGT9150 · Mar 22, 2012

apats77 said:
I've now heard that what i think is a Cat might actually be a resonator? Its right at the bend after the headers and before the first cat.

resonator's are usually after the cats, it sounds like your talking about the light off cat

Removing 2 Cats

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