I would like to know the part number of anywere for a direct fit highflow cat preffibly one u guys had experiences with an got good power gains over stock.

also could i buy this MPE-23479 (summit) dual cat on my single cat car?

 

Don't get a direct-fit for a '91 single-cat. They're only 2-1/4".

You could do the dual cat set-up. But, you'll have to do something about your cat-back as well.

 

if i did that i would have to buy a dual cat cat back then right? but it wouldnt require no tuning to run that would it?

 

Get a Magnaflow cat. You can convert your y-pipe to dual cats but it will require custom work from a muffler shop. They will also make the connection to the cat-back so you wont have to change it. However it wont be worth it unless you also get headers and a larger 3" cat-back exhaust.

For a stock exhaust setup, a Magnaflow 2.25" cat will work fine. Part number 94015 for universal fit and 93456 for direct fit.