powdrhound

Considering running catless during track season as my car no longer sees any street use. My goal is to shed a little weight from the rear of the car with the bypass pipes but primarily I would like to be able to fit a 2nd set of primary oxygen sensors that would integrate with my Motec (I have no room to do that with the existing cats in place).

The question is, do any of you guys that have swapped to cat bypass pipes have had any drivability issues with the car. Obviously the primary O2 sensors are responsible for lambda control. My weak understanding is that the secondary O2 sensors may provide some feedback to the ECU which in turn controls you fuel delivery. While a number of sources have said to simply turn the rear sensors off, I don't believe that is good advice. The suggestion I have been given is to run some type of an extender on the rear O2 sensors to reduce their sensitivity.

Any input is appreciated.

vogz

Your secondary O2 sensors are narrow-band and simply there to verify that the cat is in good working order. They don't affect fuel delivery at all. If your car is a track car only and doesn't have to pass emissions, you can simply bypass them and run a second set of wide band O2s for the Motec. Another option is to keep them in place with spacers and tap off of the signal from your factory primary wide band O2 sensors for the Motec.

Ridin Dirty

Hate cats/love dogs.

In my humble experience of eliminating cats I have observed:

-they don't weight all that much, test pipe weighed almost the same. Still have the test pipes/new never used. I ended up just hollowing out my cats. I do not recommend hollowing out...it's too time consuming...but great result.

-personally i experienced a substantial amount of "butt" hp.....the turbos seem to love it. The amount of gain seemed unrealistic/impossible but there it was...for me anyway.

-my UMW tune took care of any CELs...never an issue

"02996ttx50

i am not "following" you john except on Facebook ( twitter? whatever lol ) ..

but here's my probably useless contribution from the other sandbox: perhaps it'll help a little(?)

i briefly ran with the angled "mini-cats" ( why they call them that? i will never know ) but i suppose they are just technically the "extenders"(?) that i got from sam. they didn't work for me as i was getting cels, took em out. car ran w/out cels with the decat pipes and my kline. it was putting the cats back IN that caused me grief.

ADD: re tune and cats vs catless. my ancient cargraphic 1.3 tune, the car runs perfectly w or w/out cats. even better today, because of a new maf

Macster

Have you looked into a "catless" tune?

The goal of the ECU is to deliver an air/fuel mixture very close to (IIRC) 14.7:1 the engine because a healthy engine when burning this mixture produces exhaust gases that are most thoroughly processed by the converters.

If the #2 sensors do not supply the reading the ECU expects the ECU will vary the mixture in an attempt to get the #2 sensor readings it expects. This can lead to incorrect fueling even to the point of misfires.

What I would do in your shoes is look for a catless tune. I'm thinking with this tune 1) the engine would no longer be fueled primarily at 14.7:1 but something a bit richer and with this bit richer mixture the engine would make more power and 2) the catless tune would also I assume do away with the #2 sensors.

There is something else you can do.

Just leave the exhaust alone. The factory converters flow pretty good and the exhaust system is robust. As "ridin dirty" offered they don't weight much. (The conveter brick is ceramic or very thin metal honeycomb either of which is pretty light.)

On the track under the type of usage you would be giving the car most of the time (all of the time?) the ECU would be in open loop mode in which case it fuels the engine a bit richer than 14.7:1 (closer to the "ideal" of 13:1) and ignores the #2 sensor readings.

powdrhound

You can not use the signal from the factory O2 sensors for Motec. Motec requires the use of their specific Bosch LSU 4.9 Wideband 5 wire Lambda sensor which integrates with the Motec Lambda to Can module. The signal from the OEM Bosch sensor will not work. I spoke with one of the Motec engineers about this. He said there may be a way to pull the Lambda information from the ECU into Motec but it would have to be on CAN hi/lo like on the later 997 cars. Anyone know how lambda information is transmitted to the OBD port?

BauerR

O2 extenders don't work. I've tried every available combination.
Ultimately, I bought a Cobb and had a catless tune made. hP went way up as well as fuel economy. No negatives at all.
Filters on turbos would also be a big gain in power and reliability

"02996ttx50

i think you're right. wonder if anyone has ever used them successfully.

this reminds me of an on old vaudeville joke. i was 11 first time i heard it:

these two guys sitting on a park bench in central park.. one guy turn to the other and says:

"so, you like ***** katz?"

the other guy says,

"of course!! but how'd you know my last name"?!

the moral of the story is... hah!