Can you gut cats, as well as precats?

Discussion in 'Technical Q&A' started by gabriel, May 14, 2004.

  1. gabriel

    gabriel Formula 3


    I've seen quite a few threads about people using test pipes and gutting the precats.
    Aside from expense, why not just gut the cats, as well as the precats, and not buy test pipes at all?

    I don't want to get into a big moral debate here on the right or wrong of test pipes, and the impact, if any, on the planet, etc, etc.

    I'm just interested from a technical point of view. Is this feasible, or are there problems with such a setup?
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  3. henryk

    henryk Formula Junior

    Dec 9, 2003
    Door County, WI
    The problem would come at re-sale time. Cats are NOT cheap, so any future buyer would probably want them. Now, if the cats are bad, and need replacing, well............!
  4. Chiaro_Slag

    Chiaro_Slag F1 Veteran

    Oct 31, 2003
    Full Name:
    Plus you usually need to put the cats back on to pass smog.
  5. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
    Lifetime Rossa

    Jan 11, 2001
    Full Name:
    Steve Magnusson
    "...are there problems with such a setup?" -- no (but it would be $ foolish to destroy a decent used cat)


    I've still got 1 bad TR cat that I'd like to trade (with some cash of course) for 1 decent used TR cat -- shoot me a PM if interested.

    Or I'd work it the other way around. If you've got a 1 good/1 bad set like me and want to send me your bad one with some cash for my good one -- send me a PM.

  6. JohnMH

    JohnMH Formula 3

    Jan 28, 2004
    Dubai, UAE
    I have an '84 308 QV, the car runs well now, will the addition of test pipes in place of cats add power? Sound? Are taking a major or minor difference?

    Emissions are not a major issue for me as in my jurisdiction cars over 20 years old need not be smog tested (there are relatively few old cars around).
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  8. Mitch Alsup

    Mitch Alsup F1 Veteran

    Nov 4, 2003
    If the cat is clogged, then removing it or its internals will result in more power.
    If the cat is not clogged , then removing it or its internals will result in miniscule power at best.
  9. gabriel

    gabriel Formula 3

    Hey, Steve. I'll check the ones that I have in the garage to see if they are good, and let you know
  10. don_xvi

    don_xvi F1 Rookie

    Nov 1, 2003
    Outside Detroit
    Full Name:
    Don the 16th
    Also note that a hollow cat can make funny noises.
    It becomes a big resonator that CAN sound strange under certain driving conditions.
  11. bernardo66

    bernardo66 The Crazy Cat Man
    Moderator Owner

    Dec 14, 2003
    Montreal Canada
    Full Name:
    The previous owner of my car gutted the cat. Since the car is set up to run slightly rich, eventually the cat did get blocked. Although I don't hear any unhealthy sounds, it is somewhat louder than the average Ferrari. Luckily I live in Quebec, and our anti-pollution laws are about as effective as a Scottish pay toilet. Therefore resale in my province is not a problem, since the cars do not pass smog tests. Also, collector cars over 25 years are generally exempt from a few laws.
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  13. barcheta

    barcheta F1 Rookie

    Nov 15, 2003
    I just did this... all those worries about a clogged cat got me to thinking this would be good piece of mind. Since a good used cat can be every bit if not more than a decent test pipe, I opted for the test pipe along with an aftermarket (Quicksilver) exhaust. I have no regrets.. the car runs stronger through all gears and sounds wicked when it's near redline. You can hollow out your cats but why destroy a perfectly good one if not neccessary?
  14. gabriel

    gabriel Formula 3

    Other than the car catching on fire, how exactly do you test a cat to find out if it is in good working order?
  15. judge4re

    judge4re F1 World Champ

    Apr 26, 2003
    Never home
    Full Name:
    Dr. Dumb Ass
    Run emissions on the car. They only catch fire if the car is running very rich.
  16. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
    Lifetime Rossa

    Jan 11, 2001
    Full Name:
    Steve Magnusson
    There's two type's of cat failures IME:

    1. The supporting matrix itself is damaged -- either melting or breaking up from excessive internal temperature or from ingesting material from an upstream source (like a precat disintegrating -- which is want happened to me). Either of these is the "blockage" type failure and can be inspected visually -- on most later cats you can remove the O2 sensor for a look on that side of the matrix and there's usually an "inspection" plug provided (or 2nd O2 sensor port) for looking at the other end of the matrix without needing to remove the cat from the system.

    2. The true effectiveness of the cat can degrade if the exotic metal coatings on the matrix become fouled so it won't be doing much emission-wise like Erik suggested, but this is a more "gentle" failure (since the available flow area is not blocked). You can sometimes live with this on the older injected cars that aren't so smart (i.e., those models without upstream and downstream O2 sensors) if your emission test limits aren't too strict.

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