any difference in power output between these two combinations of header+exhaust cats
 

so I already have a "catless" (it's a high-flow cat) catback on my BRZ, and since I want my car to be able to pass emissions/not throw engine lights, I'm forced to get a header with the cat in it still.

my question is, is there a difference in power gains and even sound with the different varieties of setups?
e.g. 1. header w/cat + catback with no cat
2. header w/o cat + catback with cat.
3. no cats on either (obviously i know this would yield highest hp gains and noise increase)

First things first:

- there are not "catback" exhaust systems with a cat. Catalytic converters are in the front pipe and header
- more power to be made w/ catless header
- catalytic converter in header is no guarantee of no check engine light


So power-wise, 3 > 2 > 1
Sound-wise, 3 > 1 or 2 depending on what front pipe and exhaust you have.

-alex

None of those combos will give you any more power without a tune to back them up. With the right tune for the setup they will all be so close that it doesn't matter much.
The sound differences however can be substantial. Less cats more noise.

I noticed it says Southeastern PA in your location, would you happen to be near bucks county or philadelphia? If so the setup I have will most likely pass emissions at a local toyota dealership.

You can check here what emissions test you'll require:

http://www.ahs.dep.pa.gov/aq_apps/emissions/


For my case bucks county only requires Onboard Diagnostics and Gas Cap Check so a tune gets rid of the check engine light, and keeping the stock front pipe gets rid of most of the smell and makes it a bit less unfriendly to the environment.

Bottom line keep the front pipe cat, get a cat-less header from Gruppe or JDL will even out the torque dip the most and YOU MUST get a tune otherwise your throwing your money out the window because you're wasting fuel and any horsepower gains, and you'll fail emissions in PA in most counties because the ECU will throw out a P0420 code.

Yes, yes I know this. I was just being lazy... I have a Tsudo catback+frontpipe with a high-flow cat.

thank you for your input!

right. but will there be a difference in noise if I only have 1 cat, and the location of that 1 cat? whether it's in the header or the frontpipe? or, will that too be marginal

Yeah i live 25 min outside philly, in Delaware county. thanks for your input.

Yup, looks like you're in the same boat as me, gas cap and obd-II check, so you need to get a tune if you even have the slightest chance of passing. Also if the car is loud enough an inspector will look at the engine bay and notice a missing cat and heat shield and fail it regardless if they know this car well enough so be careful, the Tsudo system is quite loud if the car isn't obnoxiously loud, doesn't smell and doesn't throw codes techs won't bat an eyelid. Alternatively you can specifically go to a mom and pop sort of gas station to get emissions done, they'll be more lenient, or just put the stock header on for inspection the choice is yours

sounds like i have to spend more $ than planned and replace the front-pipe with one that has a cat, and get a cat-less header. I need more moneys, lol

yes, it's quite loud! However, I'm fortunate to work at a dealership where I have technicians who would help me pass inspection ;)

Having a cat is no guarantee of a quiet setup.

It's whether the catalytic converter functions as an effective resonator or not.

-alex

No issues then! You can get a Gruppe-S uel, overpipe, oil pan heatshield and gaskets for $610 and it's around $400 to get a used oft to get a nice stage 2 tune , put the stock front pipe back on and you won't regret it, however I warn you keeping the tsudo on will make it quite loud, the drone will probably be intense with any uel or EL header and that exhaust regardless of front pipe.

The variables are huge. What type of what and all that. Not a question that can truly be answered with any form of accuracy.

nope, not even looking for quietness, just the most effective setup outside of a cat-less system entirely!