Catless Headers + Secondary Cats Emissions Question

[3002 tii]

I know a lot of S54 folks here have gone CSL headers and managed to get around emissions by relocating the o2 sensors using the secondary cats but it seems really hit or miss. Has anyone successfully done this using aftermarket secondary cats like Supersprint? Also what's the most proven/consistent method, using defoulers? I know software might be an option but I'm not looking to disable the sensors since I can't pass inspection that way. The readiness codes still need to be active...

I don't own a S54 but am contemplating Supersprint headers + Supersprint section 1 cats but the secondary cats are more expensive than the headers themselves so it only seems worth it if you can use them to pass emissions.

Any advice or insight would be helpful.

[z4msteve]

I think there are a lot of questions surrounding o2 readiness with the Z4M. I haven't seen anyone even confirm if the o2 sims work or not.

[pokeybritches]

I have successfully done it on my M. My non-M was not successful due to the cats not being emissions friendly enough. In other words, they didn't clean enough crap out of the air.

The reason that it's hit or miss is because everyone wants to have as little restriction as possible and still have the secondary O2 readings remain within spec, and not trigger a SES light. If you want to be certain, go with larger cats and greater cell count.

BLUF - You get what you pay for when it comes to catalytic converters.

I used HJS race cats on my M. They are the exact cat Supersprint use, and they are expensive. They use a different construction process, much different than cheap cats. The cheap ones roll the material up like a rug and stuff it in the barrel of the cat, leaving it prone to telescoping and blowing out under high horsepower applications. The HJS cats use more precious metals, so the cell count can be less while still cleaning the air enough to be effective. Smaller cats with a low cell count = better flow and horsepower ceiling. More platinum and a unique construction process = $$$.

The Magnaflows I have were chosen because they were small enough to fit in a staggered fashion in the S-pipe while leaving the OEM resonator in place. I liked the sound of the car when it was catless, and I wanted to tone down the sound as little as possible with the cats. The cats are only there for me to say that I have them, and to get rid of the smell of gas. I will likely do the O2 sim to get rid of the SES light.

With an unlimited budget, I would have gone with HJS cats on both cars. Note that just because I had success on the S54 doesn't mean it will fool the N52.