Ok so I'm looking at freeing up the exhaust a bit. I've done some research but I was wondering if anyone knew how the 3 cats in the stock exhaust compared in their levels of restriction and pollutant removal. I'm looking to stay as legal as possible, I know tampering with a working stock cat is illegal but I figure at the least I will leave 2 cats in place. Maybe take out 1 and replace one of the remaining two with a high flow aftermarket cat. So I was thinking maybe just do a turboback with a high flow cat in the downpipe... There are so many options though. I could replace the up pipe (even though it seems like a PITA to do) and just maybe do a catback. So yeah, my question is does anyone know which cat(s) free(s) up the most power upon removal (they might be all very similar in restriction, I don't know) and which cat(s) do(es) the least pollutant removal?

 

Hey there! I am not sure on the exact level of pollutant of each cat but you should be fine removing one of them and replacing the other with a high flow cat. You are right the Uppipe is a PITA but it does free up some HP and increase how fast the turbo spools up.

Stromung just came out with a nice 3in Turbo Back that has a Primary Downpipe that has the divorced wastegate built in and then the Secondary piece next pipe after the DP has the option to either go with a high flow cat or a racepipe with no cat in it. I would go this route for your situation. Take out the cat in the Downpipe and put in a high flow catpipe.

If you are interested in one then let me know! And if you do decide to get one I am going to be running little sale on the Stromung for the month of Feb in the Vendor Classified section. Check it out!

Let me know if I can help any further!

Thanks,
Brian

Flash N Dash Performance

 

Hey man, thanks for the reply. I'll definitely check out that exhaust. I do wanna go with a quiet muffler though because I know when you start removing cats things get loud. I was thinking of coupling an aftermarket downpipe with the Borla Hush exhaust to keep the noise down a bit. So will a turboback trigger a CEL or just the up-pipe because it has an EGT sensor in it? I've heard quite a bit about CELs from exhaust work and various fixes but not a clear explanation of what causes the CELs when the different components are replaced? Is it because of the cat removal?
I understand that the up-pipe helps the turbo spool better by freeing up the exhaust before it enters the turbo but does a turboback/downpipe/catback (components after the turbo) promote earlier spool simply as a product of reducing restriction or do they just affect hp and don't really affect spooling time? Thanks in advance for any replies!

 

EGT CEL's are started because the cats are gone if you remove the stock up-pipe for a catless one you will get an CEL, or if you get a catless DP you will get one also...that is what the restrictor mod is or you can buy some from varius subaru vendors for around 15 $...

 

the thing is in california, no place has a awd dyno for smog, so they only do a visual test and basic test, so most likely anyone will pass. i tried yesterday for my gf bmw and i asked about my car and they said they just do visual and basic. lucky for awd

brandon-

 

Good to know. You think in 3 years, they will have AWD dynos to use for smog. It's cool now since they don't but who knows in 3 years.



:banana:

 

So removing the cats increases the EGT and triggers a CEL or does it have to do with another sensor that measures the chemical composition of the gas rather than the temperature? Also what about aftermarket downpipes with high-flow cats, do they trigger CEL's? (I'm pretty sure I read somewhere of some people experiencing this) I don't live in California so if I run the stock up pipe and a turbo-back with a high flow cat I should be cool on emissions right? Thanks for the replies by the way guys!

 

Catalysts are more effective at higher temperatures. But I doubt the gases cool off too much after passing through the turbo. Just my 2 cents.

 

Hey Man I am interested in the Stromung tbe. with or w/out the cat. How much? pm me. thanks

 

KmanRuffian - Hey the reason that the CEL gets thrown is because the sensor is set by the factory to read a certain way. When you remove to many cats and don't change the setting of this sensor the sensor thinks something is wrong and that is why it trips. It really has nothing to do with increased temps or anything. That is why you can get a CEL fix for it for around $15 or so because you are jut bypassing this and telling the ECU that your EGT sensor is running fine like you had a stock exhaust.

Now there is TWO different CELs...one for the Uppipe and then one for the Downpipe. Now I have heard of when people remove the two cats in the exhaust that it throws the CEL(happened to me) but I have heard that when you leave one of the cats in regardless of if it is the one in the Downpipe or catpipe that it doesn't throw a CEL. So you could replace the DP with one with no cat and then the next pipe with a high flow catpipe and there is a good chance that you wouldn't throw a CEL and you would still be doing fine on emissions! I am running no cats and can tell from the smell...but it is a good thing I don't live in Cally...lol.

Let me know if I can help further!!

wrx10404 - I will send you a PM right now!

Brian

Flash N Dash Performance