Subaru WRX Forum banner

WARNING FOR BUYING CATTED DOWNPIPES!!!

135K views 103 replies 40 participants last post by  78wrx78 
#1 · (Edited)
If you live in an area that does advanced smog testing.. don't waste your money on a catted downpipe.

I bought a catted downpipe a few years back, and had to go this month for my emissions testing.

At Advanced Smog Testing Facilities they test HC (Hydrocarbons) CO2 (Carbon Dioxide) and NOx (Nitrogen Oxide)

My Catted Downpipe allowed me to pass HC and CO2. But I failed NOx miserably!!

Here's the important part:
I spoke with the state emissions inspector (very nice guy btw) and he advised me that on WRXs... we have 2 cats in the downpipe because we don't have an EGR system. The two cats are used to break down the NOx. One cat would be sufficient to break down the HC and CO2 (just as mine was). But only our stock exhaust is able to break down the NOx.

I asked him how to reduce NOx levels without putting a stock exhaust back on. He said that NOx is produced by high EGTs (exhaust gas temperatures). Our turbo charged cars run a higher EGT than the standard car (1400degrees is common).

The only ways to decrease NOx are with alcohol/water injection, an alcohol fuel source (E85) or increasing the fuel / retarding the timing.

Retarding timing / increasing fuel would allow less fuel to be burned increasing the HC output. Alcohol / Water injection would lower the NOx level, but not enough. E85 would also lower the NOx level... but not down to levels acceptable for a 4cyl car.

Solution? Stock downpipe for emissions testing. And Catless for stage 2+
 
See less See more
#3 ·
You will pass on e85. People have passed catless on it.

Sent from my DROIDX using Tapatalk
passed NOx? and where?
 
#7 ·
In california they do test NOx, but they test you at 15 and 25mph.

In Colorado we have a full dyno test that is variable, and includes acceleration under load on the dyno. They accelerate several times up to 60 mph during this test which takes up to 5 minutes.

The state inspector advised me that he has had several modified vehicles still fail NOx while tuned for E85.
 
#8 ·
http://www.aa1car.com/library/tr1196.htm
Most vehicles that are in good running condition and properly maintained should pass an emissions test. In some cases, though, minor problems may cause the vehicle to fail an emissions test. These include:

* Engine and/or converter not at operating temperature. If a vehicle is only driven a short distance to the test facility, it may not be warm enough for the engine to be at normal operating temperature and/or the converter at light-off temperature. This will affect the emissions of the engine and may cause it to fail. Excessive idling while waiting in a test lane may also cause the catalytic converter and/or oxygen sensor to cool down enough where they may not control emissions properly causing higher than normal readings.
* Idle speed too high. A few hundred rpm can sometimes make the difference between passing and failing an emissions test if emissions are marginal.
* Dirty air filter. A restricted air filter will choke off the engines air supply, causing higher than normal CO readings.
* Worn or dirty spark plugs. Excessive plug gap and fouling deposits can create ignition misfire resulting in excessive HC emissions.
* Dirty oil. The oil in the crankcase can become badly contaminated with gasoline if a vehicle has been subject to a lot of short trip driving, especially during cold weather. These vapors can siphon back through the PCV system and cause elevated CO readings.
* Pattern failures. Some vehicles tend to be dirtier than others for a given model year because that is the way they were built. It may be the design of the engine, or the calibration of the fuel or engine control system. These kinds of problems may require special "fixes" that can only be found in factory technical service bulletins.

In areas that have plug-in OBD II emissions testing for 1996 and newer vehicles, the vehicle will be rejected for testing if all of the required OBD II readiness monitors have not run. This may require driving the vehicle for several days until all the monitors have run. The vehicle will also fail the test if (1) the test computer cannot establish communication with the vehicle PCM (defective or disabled diagnostic connector), (2) if the Malfunction Indicator Lamp (MIL) is on, or there are fault codes in the PCM. If the OBD II system is working properly, the MIL is not on and there are no codes, the vehicle should pass the test.

to pass, you need this combined part: a catted muffler..

 
#15 ·
One thing to think about when going catless, besides the environmental impact, which is obvious, is that it is against federal EPA regulation to knowingly remove the catalytic converters from a vehicle. I believe the fine is up to $50k now for a service center that removes it and $15k for the owner of the vehicle. For me, that's enough to go catted.
 
#16 ·
and you can still make big power with a cat. converter; all my previous build (minus the diesels) have been catted. Albeit larger 3" or so, but at least they were still cat-equipped.
 
#17 ·
jd92677 said:
One thing to think about when going catless, besides the environmental impact, which is obvious, is that it is against federal EPA regulation to knowingly remove the catalytic converters from a vehicle. I believe the fine is up to $50k now for a service center that removes it and $15k for the owner of the vehicle. For me, that's enough to go catted.
You're still tampering with emission control devices and breaking that same statute ;)
 
#18 ·
True... I have stock exhaust on my car and plan on keeping it that way (I'm more interested in the environmental impact than the fine). But given a choice, at least have a cat on there.
 
#19 ·
it's kinda like running off-road diesel. "if you get caught, it's like $1K-5K gal. on the first offense. some have been dealt a $10K fine first time..


Ouch..
 
#23 ·
I read an interesting tidbit somewhere...every one Prius is nullified by a catless WRX or STI out there :rotfl:
 
#37 ·
#43 ·
as awesomely interesting this battery vs water vs coal vs gas debate is, it doesn't belong here in this thread.
 
#45 ·
this surprises you? replacing the factory downpipe with an aftermarket pipe breaks federal statutes (in short -- your car isn't street legal)
 
#49 ·
Kevin, you're full of crap.

My STi passed emissions just fine the first time around with one cat (Cobb catted DP). After I let it sit for a while and had to renew it, it failed miserably. I attribute that to letting it sit for a while.

Seriously, I'm not sure why I passed just fine the first time and failed miserably the second time around.
 
#54 ·
^^ Not necessarily... Any turbo subaru has high EGTs... but NA blocks do not. For some reason the 2006/07 2.5 Imprezas do have high NOx... but only in cold weather. There was something up at the testing station regarding the 2.5 Impreza from 06/07
 
#69 ·
What does the a/f and timing mapping look like? cold air and not enough low temp fuel compensation+some advance on the timing and nox output will climb pretty fast.
 
#57 ·
What brand downpipe? What was your NOx reading? What is the NOx limit? What type of testing do they do? Idle? Drive? Dyno? Static? Accel/decel?
 
#63 ·
jd92677 said:
They don't do sniffers on OBDII cars much anymore. They only check for codes and check that all monitors have tested and passed. I did wonder how a flashed ECU dealt with monitors, I guess I know now, good deal!
You can disable codes and force readiness with Romraider.
 
#65 ·
Hey guys just a heads up from my expirience with the unhappy emmissions booths in Washington is that the tests are more strict based on regional population. So say in Seattle the test is very strict and in Po-Dunk eastern washington emmissions aren't required. I don't know if that applies country wide, but it is something to keep in mind for you area when getting ready for your car's next prostate exam.
 
#68 ·
our state doesn't have shops do it. There are state ran testing stations.
 
#70 ·
my car came catless, but i figured why pollute the environment for a 1% gain? and the smell was bad, and iit was too loud for my tastes.

so i added a vibrant racing cat and i like it alot better.

its a win-win! 99% of the performance of catless, with a 90+% reduction in emissions.
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top