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Originally Posted by jmatta
I'm back in this a couple days late, but bypass pipes are worth the money spent. I really think Porsche put these on to comply with EU noise restrictions...why else would anyone put secondary cats on a sports car?
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The 2000 and newer Boxsters are Low Emissions Vehicle (LEV) certified -- not just in California, but all US-specification Boxsters. Presumably due to their (relatively) low sales volumes, Porsche certified all Boxsters to meet California emissions regs. So, that's why the 2000+ Boxsters have pre-cats in the exhaust manifolds and the main cats in the mid pipe.
My 2000 S recently developed a crack in the exhaust manifold where the pipe meets the flange at the cylinder head. It is hard to see, but a very close examination with a bright light reveals the crack on my car, specifically at the #6 cylinder. I suspect that other areas are cracked too, but I cannot see it. The symptom is a "tick" noise which is louder at startup and becomes quieter (but does not disappear) as the engine warms up. If you have ever heard a cracked exhaust header or a header that is just slightly leaking where it is bolted to the cylinder head, then you know the sound.
Therefore, I am looking at an inexpensive solution to this problem. Are the chinese headers (ebay) really of any benefit HP/Torque wise? If so, I could relocate the downstream O2 sensors behind the main catalysts and the car should still pass the cat efficiency monitor...avoiding the dreaded check engine lamp.