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Why run any cat at all on a racecar?

Not a race car

You'll get stung for it like that, no doubt. To inspectors/police/etc, merging the wastegate pipe after the cat is the same as having a screamer pipe, albeit without the noise. It breaks the rule of having EVERYTHING that enters the engine pass through the cat converter, and they're even picky about that over here in the nanny state :action-smiley-069:

Depends which state you're in :ph34r: . There's one state that's more "nanny" than WA and I can assure you, screamers and decats are the norm.

IMO I would keep the stock cat and just run a cheapish 100cpi metal cat flanged to suit (make sure the core is welded in) because either way you're probably not going to pass an emissions test without the stock one (or close enough to stock).

Not true (true if the aftermarket cat is a generic one like most). A new 200cpi cat with newer tech coatings that is suitable for new Euro 5 cars is going to have better emissions and way better flow than a 15 year old stock cat.

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