Can I try to understand headers once and for all please?

[steved0x]

Originally Posted by Adrian Thompson

North American 986’s have 4 catalytic convertors. One in each header/manifold and one in each link pipe for a total of 2 per bank, 4 per car?
Euro (RoW?) 986’s have just 2 catalytic convertors. None in each header/manifold and one in each link pipe for a total of 1 per bank, 2 per car?

Northamerica 986 Boxster 97-99 have just 2 cats and they are in the link pipes between the exhaust manifold and the muffler.

Northamerica 986 Boxster 2000-04 have the same 2 cats as 97-99 and 2 additional cats integrated into the exhaust manifolds.

Originally Posted by Adrian Thompson

Also the catless test pipes can throw a CEL whereas the catless headers don’t throw a CEL. Is this correct so far?

On a 97-99 the catless test pipes will throw a code, because you are removing the only sets of cats from the car. But you can put a set of the eBay headers on these with no code, since you are just replacing the oem "header" with aftermarket.

On a 2000-2004, the catless test pipes will not throw a code, because that 2nd set of cats is not monitored by the OBDII system, only the initial integrated cats in the exhaust manifold are monitored. On 2000-2004 if you put an eBay header with no integrated cats, you will get a code since you would be removing the cat that is monitored.

I have a 2000 S 6 Speed with the 2nd cat delete pipes and like them. I can't answer your other questions about automatic transmission and clearances.