I snapped a couple of pictures of the OEM exhaust header after taking them off. Each weighs 3.7 kg, the cat is believed to be either 400 or 600 cel. Taking a peek into it makes you wonder how exhaust gas can flow through it without slowing down significantly. It has to be a sigificant source of backpressure. I can't see why upgrading the exhaust header would not add meaningful hp.

So did you manage to remove it without breaking off any bolts?

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Current Cars:

2008 Orange - Limited Edition Boxster S
2004 Atlas Grey - Boxster S