328 Removing Cat - what about the O2 sensor? | FerrariChat
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328 Removing Cat - what about the O2 sensor?

Discussion in '308/328' started by mike996, Oct 5, 2008.

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  1. mike996

    mike996 F1 Veteran

    Jun 14, 2008
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    Mike 996
    #1 mike996, Oct 5, 2008
    I have seen posts talking about removing the Cat and using a bypass pipe when the cars no longer have to pass emissions inspections.

    However, what happens to the O2 sensor input to the system? Seems to me that based on what I have read, the system will default to a less than optimum fuel/ignition map which might result in reduced performance, not increased performance.

    ANyone have a good reference for the specifics as to what will happen if a K-jetronic Lambda system is deprived of O2 sensor input?
     
  2. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
    Lifetime Rossa

    Jan 11, 2001
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    30°30'40" N 97°35'41" W (Texas)
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    Steve Magnusson
    #2 Steve Magnusson, Oct 5, 2008
    Just as you said, the system will default to a fixed FV duty cycle, but a good-quality test pipe will have a fitting to keep the O2 sensor in place. The O2 sensor measures the exhaust stream at the inlet to the cat (before treatment) so having, or not having, a cat doesn't really make any difference to the O2 sensor.
     
  3. Marco Bussadori

    Marco Bussadori Formula Junior

    Aug 6, 2007
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    Marco Bussadori
    #3 Marco Bussadori, Oct 5, 2008
    Just put a bung for the O2 in the straight pipes and off you go. Altrnatively you need to tweak the CO setting in your injection system if you remove the O2 sensor. It should default to an over rich mixture to avoid a lean situation. If you put the car on a dyno, you can adjust the CO screw to give you the right emission (manual should tell you the CO% in the exhaust) and balance it with enough richness to give you a reliable maximum power. Best to leave them in in my opinion, then the system does all the above for you...

    Marco
     
  4. mike996

    mike996 F1 Veteran

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    #4 mike996, Oct 5, 2008
    Steve, OK, got it. I was thinking that the O2 Sensor was DOWNstream from the cat and would therefore be seeing something different if the cat was removed and a bypass pipe installed, even with the o2 sensor in place. But as you said, if it is before the cat anyway, it would make no difference at all whether the cat is there or not. I thought I was looking at the O2 sensor in the parts diagram but in looking closer I see it was the thermocouple - which, I assume, triggers the slow down light if necessary. A new replacement cat or a bypass pipe does not appear to me to have a fitting for that thermocouple, just the 02 sensor.
     
  5. mike996

    mike996 F1 Veteran

    Jun 14, 2008
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    #5 mike996, Oct 5, 2008
    I got a couple of emails re this so I wanted to add - I was just curious about the technical side re the O2 sensor - I am not planning to remove the cat and install a bypass pipe. No dyno test I have ever seen or performed produced more than 2-3 HP by removing a cat and some engines lose power. If I replace my 328's oem 20 year old cat, it will be with another cat, not a bypass pipe.

    I saw an add from one company that claims a 20-50 HP gain by putting on their bypass pipe. I wonder what they're explanation would be if someone installs it, checks it on a dyno, finds somewhere from minus 3 to plus 3 HP and asks, "What the?" I'm sure the company has a "good" explanation for why it didn't work "In this particular case."
     

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