JohnCK2014

A couple of years ago, I replaced both cats in my 02 C4S. I decided to go with the OEM cats. Now two years later, I am getting a fault code saying my left Cat is not performing to standard. That might be the result of an O sensor going bad and not the Cat. I am in the process of figuring out if that is the case. If it is the Cat, I have a few questions for the board.

1. Is it true that tracking the car, which I do about 6 or 8 times a year, cooks the cats such that two years is about all you can expect from them?

2. Has anyone put on the universal high flow cats. In shopping for cats, the OEM cats are about $700 for each side. There are, however, high flo universal cats for a lot less money. I know the OEM ones just bolt on and the universal ones do not and require a bit of modification. Will any good exhaust shop be able to modify and bolt on the less expensive universal high flo cats? Does that work? Is it worth it? I would love to have the extra horsepower and better sound of a high flo cat. And to be able to do that for the same or less money would be wonderful. Has anyone used the universals or am I just dreaming here?

808Bill

Swap your sensors to the other bank and see if the code follows...Report back.

JohnCK2014

That is what I am doing. But, if it isn't the Cat this time, it will be the cat at some point. And I would like to hear thoughts on replacing them. As much as I would love to splurge on some Fabspeed high flow set, I am not going to do that if tracking the car as much as I do means replacing the cats every two years.

dkraige

I ran 37 track days over 4 years before my cats failed, and at a total mileage of ~93,000. That's only 1 data point though, and I can't say how much the tracking ruined the cats vs. just 93,000 miles and 19 years of use.

I just installed Topgear 200 cell cats yesterday (https://www.topgear-eurosport.com/po...ll-sports-cats), as they were the cheapest option I could find for new converters. Fitment was super-easy, other than having to re-route the O2 sensor cable slightly; there's no need for extensions as other posts have suggested, it's just that the downstream (gray connector) ones will no longer fit in their nice little clips, so you have to zip-tie them to some other stuff to keep the wires tidy and safe.

Have not been able to run the car yet as I'm waiting on some unrelated parking brake parts before I can put the car back together and have it roll. Will report back later as to how they are performing.

By the way, there is ZERO reason to remove the rear bumper to remove the cats, at least on my MK1 Carrera. Perhaps the MK2 or C4S are different with their different bumpers. Easy job from under the car without taking any bodywork off. The only challenge is the bolts connecting the cats to the headers. If you're lucky you can get enough grip on the nuts to unscrew them, or shear off the studs. If you're unlucky and they're rounded/rusted beyond gripability, get ready for some cutting. I ended up being able to unscrew 3, break 1, and had to saw 2.

dkraige

Reporting back. Have run the car a couple times with the new cats. Sound is considerably louder than stock cats. Particularly noticeable when the car is cold, like when I'm trying to leave my neighborhood without making a scene. Anything more than 5% throttle might rattle windows. After they warm up it seems to actually get a little more mellow sounding. I'm not sure if this has more to do with the cats or the mufflers; I've noticed this characteristic of the Milltek mufflers I've had for several years, that they sound a little more staccato when cold and then get more of a warm, smooth sound after a few minutes. The system is also noticeably louder at big throttle and high revs. It has kind of a "raspy" sound to it, not sure if I like it yet or not. Quite a bit higher-pitched and more violent sounding than the OE cat / Milltek combo, which was very low-pitch, almost more like a V8.

Cruising on the highway or any other "maintenance throttle" situation I don't think there's a significant difference. It's just noticeable when trying to be quiet in town, or when accelerating hard. And if you do a good matched-rev downshift, everybody in the county will know about it

Ran O2 sensor data with Durametric while driving and it appeared to show all the good things; oscillating voltage on pre-cat sensors, steady-ish voltage on post-cat sensors, so hopefully no CELs will return. Will report back again if and when the world allows me to drive the car a lot more miles to get some more data.