Whats a good high flow cat?
 

1997 xj sport 4.0. Damn thing was rattling so I beat the inside out and now it's too loud!

Magnaflow is the highest rated high flow catalytic converter I know of. If mine goes I would replace it with that. I am just not a fan of there mufflers. Can't win them all I guess.

Mudfrog, one of the vendors on Cherokeeforum.com sells some excellent cats...have had one for over a year and no issues, great price, easy install!
Link to catalog
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Most aftermarket converters are 400 holes psi (OE converters are 500). True High flow converters are considered 300 hole psi or fewer.

I run a 300 cell Thunderbolt on mine and it greatly increased the loudness over the 400 cell MagnaFlow I had. If your concerned about the sound go with a 400 cell converter, on our 4.0's you really will not notice much of a difference in performance.

I have a Magnaflo cat and Dynmax cat back andI love it. It sounds great too!

I've always used Catco.