I see, and do you have some kind of dyno results to back up your claims? I've noticed a fad lately with people replacing their stock cats as another bolt-on and I can't say they're having very impressive results. All of the information I've seen points to the fact that the stock cat when mated with a header and catback designed to bolt up to it imposes no large restriction in flow.

There are two situations which merit the stock cat being replaced:

- When larger piping is used, it does indeed become a restriction but the smaller-diameter pipes do not flow well enough such that the stock cat would be a bottleneck.

- Deposits of smog particles and other grime get cooked on to the matrix and become physically bonded to the surfaces. These deposits grow over time and eventually limit the ability of the cat to flow. Cats are considered a wear item because of this.

Unless one of these two situations occurs, there's really no reason to replace the stock cat.