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Old 01-23-2004, 11:38 AM
mgoulde mgoulde is offline
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Location: MA
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Mein Auto: Z3 3.0 Roadster
Removing catalytic converter for racing

BMWCR Prepared and SCCA ITS let you remove the catalytic converter. Has anyone done this? What did you put in its place between header and muffler?

1. Any power gain?
2. Any weight savings?

SuperSpring makes a racing only resonator, but I'm not sure what I'd gain (for $350).

Any thoughts?


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Old 01-23-2004, 12:56 PM
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tim330i tim330i is offline Founder
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Mein Auto: Ti Silver 03 M3
If you have OBDII (Post 96) you will throw check engine codes as the DME (ECU) is looking for the post cat O2 sensor to show a difference.

Not sure on the Z3s but E46 have the cats built into the headers for US spec so "swapping" them isn't something simple.

getting aftermarket headers and high flow cats mounted down stream should show a nice power gain from the improved header shape. Removing the high flow cats for racing seems a bit extreme to me.


PS I could be wrong because i know nothing about z3s but it would seem to hold true based on US emissions regulations.
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Old 02-02-2004, 04:58 PM
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TeamM3 TeamM3 is offline
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the typical fix for the downstream O2 sensors is to replace them with simulators that generate a "proper" signal to fool the DME. I know the TCKR Z4's are running without cat's in Grand Am and TC told me they were using the OE software programming, so there must be some way around it

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