Kepp Cats on or by pipes?

[Firebirdcrazy]

My catalytic converters are bad, and I purchased a used set just to get me past inspections. I have an idea I want to do with the old ones. I am thinking about cutting the old cats and weld on straight pipes in the original location and put them on after inspection. Is this a good thing? or should I just leave the cats on? I know there is an increase in horsepower but is it worth it? Any ideas?

[raroZ28]

It's what I did. The sound is great. A lot of people don't agree with it. But it's your car, and if they have emissions where you live, I'd say it isn't worth it. You will not pass without it. Get a high flow cat. It will flow great and it beats hacking your exhaust up for every inspection.

[Firebirdcrazy]

Once I pass inspection thats when I will do the change. In Nj the state inspections are now every 2 years which is a good thing. The sound is great but how is the feel inside the car? I get a lot of interior resenonce as it is with the American Thunder Flowmasters. Not that I mind though lol. Is there vibrations in the interior?

[Jeff_in_Atl]

How do you know the converters are bad? Just because it didn't pass emissions may not mean they are bad. A bad O2 could cause the emissions to be out. I find it hard to believe a 5 year old car has bad converters on it. My 11 year old car passes emissions with flying colors on the factory cat.

Also under federal law the emissions equipment have to be warranted for 80,000 miles. I had my air pump replaced at around 90,000 miles and ~7 years old under warrantee because it was emissions related. They didn't hassle me at all which I was surprised about.

[raroZ28]

Also under federal law the emissions equipment have to be warranted for 80,000 miles. I had my air pump replaced at around 90,000 miles and ~7 years old under warrantee because it was emissions related. They didn't hassle me at all which I was surprised about.

Jeff, I think the AIR has a recall on it, doesn't it?

[Jeff_in_Atl]

Jeff, I think the AIR has a recall on it, doesn't it?

Yes it does. But they said I was out of warrantee for it but since it was emissions related they had to fix it under federal law. I was like hey go for it. LOL

[Firebirdcrazy]

I have 102,000 + miles on my car, and I put the scanner on it. My drivers side cat shows its been frying up hot, and way below inspection regs for NJ. It already failed inspection so when the car goes in to the paint shop this week they will replace them for me at the same time. Once it passes I will just remove them again.

[JL8Jeff]

Get a pair of high flow cats then. I put the Pacesetter longtubes on my 96 SS and I added a pair of cats to the y-pipe. You can smell the difference so if you ever get pulled over, a cop might notice and check your car. Without the cats you could get fined or they might even force you to fix it. I don't think it's worht the hassle to run around without cats. I got some brand new 3" high flow cats off Ebay for around $70.

[Jeff_in_Atl]

I have 102,000 + miles on my car, and I put the scanner on it. My drivers side cat shows its been frying up hot, and way below inspection regs for NJ. It already failed inspection so when the car goes in to the paint shop this week they will replace them for me at the same time. Once it passes I will just remove them again.

Just curious, What does an OBDII car's computer say about the cat? Does it show the percentages for NOx and the other stuff they check for? Does the after cat O2 do anything to change fuel mixture or is it just a monitoring O2? Does it show the temp of the converter. They are supposed to run at like 1500 degrees.

[Firebirdcrazy]

I will get the print out and see the numbers.. I got 102,000 miles out of these cats cant really complain.. Besides my clutch the only thing that has now just gone bad was my water pump so I just replaced it with the thermostat, and hoses, and my cats. I think for being driven hard my girl has held up really well.

[Joe 1320]

If you do away with the cats, expect the exhaust to be a bit more stinky. Not only that, the cats do cut a bit of resonance.

[94firebird]

keep them on

I bought my bird with no cat, and the first weekend i had it I took it to the shop and had them put everything on new from the Y-pipes back. My exhaust used to smell really bad, and with the t-tops off or even windows down, at a stop light you would come close to passing out. The horsepower increase is not very noticeable without them, and I actually got a little more bottom end power with the cat in because of the increased backpressure.

by the way, if youre ever getting a stock exhaust replaced with a stock exhaust, make sure you get the dual tailpipes, it is only 30 bucks more and sounds and looks a hundred times better. Even makes my v6 sound somewhat throaty.

it also kept the interior resonance centered towards the backseat and trunk area, so you can only hear it behind you.

[Injuneer]

Just curious, What does an OBDII car's computer say about the cat? Does it show the percentages for NOx and the other stuff they check for? Does the after cat O2 do anything to change fuel mixture or is it just a monitoring O2? Does it show the temp of the converter. They are supposed to run at like 1500 degrees.

The PCM has no information regarding the quality of the exhaust gas, other than an indication of how much oxygen is in the exhaust stream. The after-cat sensors do nothing other than measure (by inference) whether the cats are working or not. They do not control anything. There is no temperture measurement.

If a cat is getting excessively hot, as mentioned by Friebirdcrazy, it could be an indication that there are major misfires on that side, and the fuel and air that isn't igniting in the cylinders like its supposed to is burning on the cat and overheating it. I wouldn't jump to the conclusion that an overheating cat is defective. A defective cat would run colder because it would not be promoting the exothermic reactions of CO to CO2 and burning the unburned HC's.