Old flat bed cats where restrictive, first gen 3 ways, better but still a little restrictive, modern standard oem still a little restrictive as they have to last 8yrs, 80,000 by law, modern oem performance cats are pretty damn good due to the fact most of those types will never see the 8yr, 80,000 mile mark( if the hellcat at 700hp can use them, 600hp mustangs, 600hp vipers can use them without hurting performance and they are sized to flow more CFM than the motors can generate) and modern high performance cats have next to zero flow restrictions...no reason not to run a new spun cat, especially since any motor cammed is an emissions nightmare with higher HC's than stock due to increased overlap and higher N2O at rpms. A spun cat refers to the outer case being spun therefore much smoother transitions and a true Highflow cat will be 100-300cpi ( cells per inch) with a wound metal substrate instead of ceramic brick...and typically a more expensive cat will be a much better cat as the rare metal loading is typically higher ( platinum, rhodium, palladium, and even gold are very expensive...a 40 dollar cat has very little metal loading)
