Originally Posted by
7milesout
I studied a bit. So, we have 2 cats. But my assumption is that the first cat takes all the beating and is probably 90% likely to be the one with the issue. If it were me, I would consider buying the $371 cat from rock auto. It comes complete to the manifold. However, I'm not really trusting that manifold, I'd have to eyeball the stock manifold to see how similar it is to the one pictured on rockauto.
If I lived in a location that did not do emissions testing, I would simply pull the stock manifold and bad catalyst off, and replace it with one of the "performance" headers that have been discussed in these forums. Not for the "performance" aspect of it, but as a way to eliminate the catalyst. In littlemoule's case, if that catalyst is plugging, and he put a header on it with no cat (but a bung for 02 sensors), I think he would see rather large performance gains.
The downside is, I think he'd be getting cat efficiency codes. Which I could live with if I KNEW that the codes were simply telling me that the catalyst that I DON'T HAVE is not working effectively ... and if the car was running good.
littlemoule - A lot of the Magnaflow cats I saw looked like the 2nd cat in our system. So, you'd have to be sure you're getting the correct cat for fitment reasons. The Magnaflow stuff looked like decent or better quality though. The first cat (on the 2020 which is what I looked at) appears to bolt into place. No need for welding. But gonna need good impact tools to remove those bolts.
2014-2015 have different exhaust from 2017 and newer. 14-15 have a seperate exhaust manifold where the 2017+ have the cat and manifold built together. Then the exhaust from the back of the front cat to tailpipe(which includes the rear cat) are different lengths between the 2 styles too. It's not a noticable difference unless you have the two side by side. That's why that header that you can buy for these cars doesn't fit the 2017+ style without shortening or lengthening(I can't remember which) the rear section of exhaust.
I've heard of spark plug defoulers being used to relocate the rear O2 sensor so it doesn't read the same as the front O2 but I'm not sure if that'd work in these cars or not. They can be pretty finicky about the electromagicals.
I have had pretty good luck removing exhaust bolts on these things but certain areas out east can turn to metal into orange dust pretty fast.
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