cat converter question....

hey i was wondering about all them catalytic converters out there.... like on ebay they have all these different types of cats for every car and they all look the same to me, i was thinking "wouldnt any cat fit on any car?" or would there be a problem with putting a cat from a civic onto a prelude? even if it's a racing straight through cat?

i think they are all the same could be wrong though

They all do the same job, but the pipe diameter and flanges differ. Best bet is to get a custom "high-flow" cat to open the system up but maintain EPA standards.