Catted vs catless DP - Subaru WRX Forum
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#1 Old 02-03-2014, 12:59 PM
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Catted vs catless DP

I know this has probably been talked about before, but I'm on my phone and I couldn't find what I was looking for, I did search. But I am about to go past my warranty, and am gettin my tax return soon so I would like to go stage 2 with my car. My question is what is the difference between catted and catless DPs? Beside the cat, obviously. Like what are the pros and cons to each? I have also read that catless tend to create boost creep.. What is this? Also what brands have the "best" DP for the money, as far as sound, performance, etc.
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#2 Old 02-03-2014, 01:11 PM
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Depends on your state's emissions. I have a catless and live in Colorado so i have to "find a way" to pass emissions testing each time it is due. From my experience, catless has a minor minor improvement in HP over catted.
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#3 Old 02-03-2014, 01:13 PM
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also forgot to mention that if you find a good tuner then issues with catless is not really an issue......My tuner in Parker Colorado works wonders on my car and i am running a catless downpipe. IMHO, protune is the way to go. I really do not trust those little COBB AP, just my 2 cents
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#4 Old 02-03-2014, 02:31 PM
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The reason we have CATs at all is to limit the SMOG that burning petroleum based fuel causes. the catalytic converter is a platinum based honeycomb that bonds to un-burned fuel and burns them in the heat of the exhaust path. a CAT-less downpipe simply removes that honeycomb thereby allowing exhaust gasses to move more freely to the CAT-back system. the lower overall air resistance of a CAT-less system means that the engine does not need to work as hard to exhale exhaust gasses. The HP gains are usually minimal but they ABSOLUTELY require a tune. A decrease in exhaust resistance can cause the turbo to spool faster than expected, / Over simplified/ when the turbo spools faster it crease more boost which in turn leads to more exhaust gasses to push the turbo faster and faster, they call this condition boost creep (when your turbo is spinning overly fast and increasing boost respectively) Boost creep can be controlled with a good tune and with properly setup boost controllers, BPV and BOV.

Im not sure what the regulations are like on Ohio but here in Cali they are sticklers for emissions standard. In Cali we have a visual inspection where the ref will look under the hood for hexaust modifications and then they use a device to find exhaust problems. it would be very hard to pass the sniffer test without the OEM number of cats in CA.

I might also look into a divorced DP, they allow for less turbulence than the OEM but they still pass the gasses through a CAT giving decent sniffer numbers.

TLDR; Cats are there to fight smog, It may/may-not be kosher in Ohio, Look at CATed divorced DP for the best of both worlds. IMHO

Jason
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#5 Old 02-03-2014, 04:02 PM
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Thank you! That helped a lot, I may have heard that there aren't that strict of rules on it but I could be wrong, I'll have to look around some more

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#6 Old 02-03-2014, 04:34 PM
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Quote:
Originally Posted by lfuller1988 View Post
also forgot to mention that if you find a good tuner then issues with catless is not really an issue......My tuner in Parker Colorado works wonders on my car and i am running a catless downpipe. IMHO, protune is the way to go. I really do not trust those little COBB AP, just my 2 cents
He is correct. I only trust Cobb OTS AP Tunes for Stage 1 purposes.
Once you go DP (Catted or Not) Stage 2 OTS maps are not in my mind.
I rather get Protuned for Stage 2 because OTS Stage 2 maps are known for Motor Problems.
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#7 Old 02-03-2014, 05:17 PM
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i just met up with another scoob from around me in the dayton area, and he said you are allowed to run catless in ohio. and i would get it protuned, there is a guy here in our dayton scoobs group that is the "group tuner" so im told
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#8 Old 02-03-2014, 05:24 PM
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If you go catless the Cobb ots maps aren't really meant for catless, they were meant for a catted dp. Just food for thought.

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#9 Old 02-03-2014, 05:26 PM
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Every state is different, some states don't allow being catless but don't physically check during emissions testing. I've never heard of any one I know personally being stopped by a cop and having his downpipe checked, but theres always someone who knows someone on a forum who said something about a guy he knows who got a ticket for it.
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#10 Old 02-03-2014, 05:50 PM
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also i have a stock exhaust with muffler delete, dont know if they would change anything with the downpipe
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#11 Old 02-03-2014, 09:02 PM
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Divorced is never truly divorced or it'd have to cover the area where IWG is and eliminate any gases cross over. Which it won't truly seal the IWG gases off from the normal exhaust gases. It's a lose lose scenario. Don't even bother. Go with a bell mouth DP and if you want to separate the gases...get a EWG.
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#12 Old 02-04-2014, 07:50 AM
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I have a TurboXS catless TB exhaust and it sounds amazing! Still trying to find a way to pass emissions testing though.....keep your catted downpipe for emissions. I threw mine away for some unknown reason after I went catless. In hindsight, not so smart.
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#13 Old 02-04-2014, 11:23 AM
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Quote:
Originally Posted by turmic View Post
Divorced is never truly divorced or it'd have to cover the area where IWG is and eliminate any gases cross over. Which it won't truly seal the IWG gases off from the normal exhaust gases. It's a lose lose scenario. Don't even bother. Go with a bell mouth DP and if you want to separate the gases...get a EWG.
The idea behind a divorced setup is to direct the gasses down the same path and create a more laminar flow of exhaust and vented boost. It wasn't designed to separate the gases entirely, only to prevent turbulence. CATs work best under laminar flow, meaning that the exhaust gasses are flowing in a straight line rather than bouncing off the walls of the exhaust.

Jason
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#14 Old 02-04-2014, 10:02 PM
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I'm not confused...its meant to not disrupt the flow of the IWG gases. That way you don't have wastegate issues. But, what do I know....

Kirt
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#15 Old 02-04-2014, 10:23 PM
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Didnt think you were confused, just trying to provide OP with as much info on CATs as I can

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