I've done quite a bit of search on this subject but not much answers to my specific question. So, let me try to put it out here.

Now, I am running a DP, Stock Cat and Straight 3" pipe in the back (also full intake and M2 MIC. From previous tests (acceleration, not dyno) I have realized significant gains from the 3" straight pipe CB vs other CB systems I tried. This config gives an irregular exhaust note but, not too loud for me. Also my acceleration tests from many years ago indicated negligable gains when replaced the stock cat-straight pipe combo with a MP-twin tip Borla CB combo.

My question is if anyone compared (Dyno or other) a high flow cat against a stock cat? I really do not understand how a much smaller sized high flow cat is able to flow better than the stock which has far larger surface area. Taking it further it is also important to note that with the stock cat I can run the straight pipe CB but, with a high flow cat it MAY be too loud. (Would it be much louder?) Thus, the potential gain from the high flow vs stock cat exchange could be lost if I have to use one of the regular CB systems.

Any concrete tests or experiences out there for these variables?

Thanks

 

there are a few differences between a high flow cat and the stock cat.

1. the overall diameter of the exhaust pipes b4 and after the cat are larger on the high flow cat - 3" for high flow vs. ~2.5" for stock.
2. the larger surface area of the stock cat has little if anything to do with the gains from switching to a high flow.
3. a high flow cat made of a ceramic core will be slightly louder than stock, but not by much.
4. most people don't have issues with overall loudness when using an appropriate muffler is used. having a 3" pipe after the cat w/ no muffler is ******* loud.

you can go to wargarm's site to comare dyno sheets of cars with various configurations. the link is in the single turbo sticky iirc.

 

Actually, the inlet and outlet of the stock cat is quite a bit smaller than 2.5" because the flange is welded on the inside.

I have a Cheap Bastard intake, downpipe, high flow cat and a RB dual exhaust and my car is not significantly louder than stock except at WOT (and even then it is not obnoxious).

 

my magnaflow hiflo cat is a lot lighter than the stock one,it makes my rb catback sound better too.The car also felt a little faster with the magnaflow.

 

Oops I bumped the wrong thread.