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Removing cats permanently - is a test pipe all I need?

Discussion in 'Gen 2 Prius Accessories & Modifications' started by Waco440, May 10, 2020.

  1. Rmay635703

    Rmay635703 Senior Member

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    I’ve often wondered what the ACTUAL emissions looked like before and after a CAT napping on my old Honda NOx went up as did CO but it seemed like the overall pollution wasn’t much different before and after

    YMMV
     
  2. oldtechaa

    oldtechaa Active Member

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    Here's a graph based on the World Bank data:
    How do catalytic converters work? - Explain that Stuff

    CO is 1/7 of no cat, HCs are 1/6 of no cat, and NOx is 1/3. That big of differences can have a serious impact on health and without cats would literally have killed thousands and thousands of people since the introduction of cats on cars in the US.
     
  3. Rmay635703

    Rmay635703 Senior Member

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    on the older lean burn Honda’s that came both with and without cats from the factory the difference was not that dramatic, much of the emissions controls are due to “other” changes with the engine valves and ECM controls working with the cats behavior .

    the reductions seen Recently are simply impossible just by strapping a cat on

    real data off his car would be ideal, my guess is that specific emissions will go up a lot but others won’t move much

    ah well
     
  4. oldtechaa

    oldtechaa Active Member

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    A lean burn engine probably also is running a two-way converter, which is much less efficient and would create a smaller difference. Pretty much all car engines use three-way converters, which have a much larger impact.