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Since I'm local, I emailed Jack to see if he would be interested in doing some dyno sessions with my ESS Z4M. It's got a stock exhaust now, but the seller is including Euro headers with the sale. I'd like to see a comparison between stock, Euro, and CPI headers + section 1 to see exactly what we're getting for our money.
I think the E46 M3 only has one cat in its section 1, so I'm not sure if those guys can relocate the O2 sensors like we can in the Z4M. Even if they can, with half the cylinders having a straight pipe to the muffler (no resonated X-pipe like we have), the M3 has rasp issues. We have dual cats in the section 1 and a resonator in the X-pipe, so the need to remove rasp isn't the same for us.
Our motivation boils down to power and ease of secondary O2 sensor install (no welding bungs). If the CPI section 1 made a consistent 5 horsepower over stock, the it would be worth it IMHO.
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