If the cats are well designed they should make fairly little difference. For all the more that people will talk about them restricting flow, if you look at how they are designed they should still maintain the same flow area as the pipe before or after them. That's why they are larger diameter than the pipe. The stock ones expand from 2.5" to something like 4" or more. A 2.5" pipe has an area of ~5 in^2. A 4" pipe has an area more like 12.5 in^2. That means the substrate inside could block off nearly 60% of the flow path and still maintain the same amount of flow area as the 2.5" pipe feeding it.
Generally speaking though the car should be able to adjust for it reasonably well. I know I talked with my tuner both when adding cats and when moving to 3" exhaust and he said there was no need to bother changing anything. The car did drive noticeably different to me initially, but the adaptives gradually bring that all back into line. Worst case I'd talk to your tuner about it if you are concerned. Guessing just taking cats out shouldn't make as big a difference as something like changing manifolds or exhaust size.
Generally speaking though the car should be able to adjust for it reasonably well. I know I talked with my tuner both when adding cats and when moving to 3" exhaust and he said there was no need to bother changing anything. The car did drive noticeably different to me initially, but the adaptives gradually bring that all back into line. Worst case I'd talk to your tuner about it if you are concerned. Guessing just taking cats out shouldn't make as big a difference as something like changing manifolds or exhaust size.
