Catalyst cell sizes

[5000SE]

Not for a Rover V8, but for a Jaguar XKR.

The car was fitted with aftermarket exhaust and freeflow cats, 200cpsi as opposed to normal 400cpsi (cells per square inch).

The substrate has broken down in the cats I have, so I'm buying universal replacement sports cats and welding my inlet/outlet pipes onto them (the exhaust manufacturer wanted £500 plus vat per cat to refill them!!).

I can also get 100cpsi cats, but I've heard differing views as to whether they will be able to pass MOT or not - does anybody have experience of this?

(In my case, it's a 1999 car).

[davehoos]

some systems have problem with the after cat O2 sencor setting failure codes or driving at a reduced power output when aftermarket cats are used.