I agree with you on the test pipe vs hi-flow race cat issue.I would personally rather use a hi-flow cat. Unfortunately more than a few of the race cats will throw a CEL almost as quickly as a test pipe. I had an awesome 3" turbo-back from M2 on my WRX and had to run a MIL eliminator to keep from kicking a "cat efficiency" CEL.

The nicer stainless race cats are more expensive but seem to be much more effective than the cheap ceramics. I ran a Milltek turbo-back on my 337 and never saw any issues (except a lot more power;-)

BTW-Using a MIL eliminator is not that big a deal though, as it does trick the back 02 sensor into seeing an 02 value that is within spec. As far as the MIL eliminator covering up a legit CEL, I am not sure other than a real cat problem, what kind of problems you would be covering-up?

 

most test pipes also have a threaded hole for the oxygen sensor
to keep the cel from turning on

 

 

Hahaha you can't fool me, those guys aren't looking for newbies, they are searching for weapons of mass destruction!

As far as the test pipe having a threaded 02 sensor hole...that alone won't keep CEL's in check. The catalytic converter acts as a super heater which, if working correctly, will help burn-up unspent fuel and cumbustibles that make it past piston combustion process. The pre-cat 02 does a value check and expects to see a cleaner mix downstream at the post-cat 02 sensor.
Obviously a straight test pipe will have the same pre and post-cat 02 values which will set a CEL. The only way to keep CEL's from popping is to create the voltage value the post cat 02 expects to see by installing a mil eliminator on the post cat o2 sensor wiring.

Works great and easy to install!

 

...call him a newbie, just make sure you have that fine money handy...

 

My car has the o2 sensor before the 2nd cat, I put my test pipe on yesterday with the o2 sensor back in place and don't have a cel on at all.

 

Don't have cell on my car either and i'm no cats. Got RRM header and test pipe. HMMM... could it be the that the O2 values are well within range since our motors are so efficient with its four vlv hemi head technology?? Maybe it is due to the efficiency of the turbo settup?? Better yet maybe it is because the O2 value is not really a faultable reading, it is used just for real-time AFR/timing map adjustments... with that being said then the O2 sensors only other role is that of a temp sensor, which is a faultable reading. Thus if you removed the cats you'd be flowing the exhaust so good that the temps would remain low and be out of the range throwing the CEL light on. This temp variation happens when a CAT gets clogged, resulting in high temps, or when a CAT is worn out resulting in low temps. Basically what N10S was leading into.

On that note i like the no cats for the power and sound as well. But i'm not against cats at all. They are a proper measure for the environment.

 

I also have a "test pipe" (no cat temporarily installed, ya know,, for testing) and have not gotten any codes eitheir. I was a bit suprised and begining to wonder, I am glad to see that I am not the only one with no codes. I am also wondering if there may be some differences between EVOS sold in places like CA and the rest of the world. I know the FD's had a CA version that had additional emission equipment on them, could that be what we are seeing here? But with maybe just slightly different CPU code?

 

You can't run leaded race gas with a cat installed on the car.