I have an 88 l98 formula. It currently has a single cat i would like to upgrade it to the n10 dual cat set-up. What parts would i need to do this and where can i get them? do i have to do anything with the computer? any help would be great.

A single high performance aftermarket cat would flow better than the factory dual cats.

yes, the CATCO 3 inch 9118 cat is popular

what about the aftermarket dual cats for our cars...

It's a waste of time. Get an aftermarket 3" mandrel bent Y-pipe with a high flow cat and you'll be much happier.

Most people convert AWAY from dual cats. Why on earth would you want to convert TO it? It isn't going to make your car faster.