(Stock Exhaust + Hi Flow Cat) VS Catback?
 

After having an Apexi N1 catback for the last year, I'm looking for a quieter setup. Can anyone comment on the horsepower loss/loundess level drop associated with going back to the stock exhaust and running a high-flow cat? Will the sound with the HF cat be any higher than stock? Will boost creep be an issue with the HF & stock exhaust...is tuning the HF cat more difficult?

Hi flow Cat ? ? ?
 

By stock exhaust do you mean your still running the precat, main cat with a Apex N-1 and want to keep the precat, and go to a hi-flow cat with a stock cat back ?????

I jsut went from a DP, clogged stock cat, N1 duals, to DP, hi-flo, and stock muffler. I have to say it's a lot quieter now than it was before with a clogged up cat. I cant really say anything on the power issue, because my cat was clogged. Hope it helps.

I just but a High-flow on this weekend. I now have a DP, high-flow and the stock cat-back. The noise level at idle is slightly louder, and it seem to be loader while getting on it. I'm not sure how much louder than before but it is noticible. Sounds better to me. And it gets nice and low during decel. :)

I did notice a bit more power in the upper half of the RPM's, specially when the second turbo comes on. I didn't have any trouble with creep or spiking, But I am also using the PFC to control boost.

Yeah, right now I have a DP, stock cat and the Apexi duals. I just can't take the drone anymore. If I could get about the same power by swapping the Apexi for a high flow cat I would do it in an instant. Now that this issue has been raised, how many HP is a good cat back good for over the stock muffler? . I recall this being discussed many times but I forget the conclusions made.

Why not keep the stock cat and go with a quieter cat-back exhaust such as Racing Beat or M2?

I can't give you a hp number but if you put the stock muffler back on your car it will seem anemic to you after having an N1-Dual. I did it temporarily after selling my N-1 Dual. It was awfull. The stock muffler is so quiet because it is also very very restrictive. Power loss was mostly noticible on the bottom end, because there was no more bottom end.

As Rynberg says, stock cat and a quieter aftermarket cat back is a much better way to go.