gutted cats and wired open exhaust bypass valve | FerrariChat
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gutted cats and wired open exhaust bypass valve

Discussion in '348/355' started by skierlawyer, Jul 7, 2011.

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  1. skierlawyer

    skierlawyer Formula Junior

    Sep 12, 2010
    385
    Golden, CO
    Full Name:
    Brian
    #1 skierlawyer, Jul 7, 2011
    I have searched and read everything I can find on these topics. I am curious what is best for the health of the car. Stock cats or Gutted cats? Exhaust bypass left alone, or wired open?

    The F355 I recently purchased came with a set of OEM Cats and Gutted ones. The previous owner ran the car with the gutted cats and the exhaust bypass wired open. The car sounded amazing. When I purchased the car he put the OEM cats back on and un-wired the exhaust bypass valve to go through emissions.

    Now I have the car and am curious if I should put the gutted cats back on and/or if I should re-wire the exhaust bypass valve open. The car currently has a stock muffler.

    Thanks
     
  2. roadracer311

    roadracer311 Formula 3

    May 6, 2009
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    Paul
    #2 roadracer311, Jul 7, 2011
    I've heard people say that it's bad for the car to wire the bypass open. I'd be more worried about losing mid-range power with the bypass open.

    Did you get a gutted Y-pipe too? Since that's the part the car does most of its screaming through, I'm surprised more folks don't gut the bypass cats instead of the regular cats.

    I'd rather my 355 be quieter at idle and scream more on the bypass.
     
  3. pourquoi_ne

    pourquoi_ne Karting

    Mar 16, 2006
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    John
    #3 pourquoi_ne, Jul 7, 2011
    Gutting the Y-pipe doesnt make a great deal of difference to the sound, I found.
     
  4. roadracer311

    roadracer311 Formula 3

    May 6, 2009
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    #4 roadracer311, Jul 7, 2011
    Interesting. Thanks for that data point. I've been thinking about trying to find an old one (preferably one that has already mostly failed) and gut it.
     
  5. Monteman

    Monteman Formula 3
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    Feb 9, 2006
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    Santa Barbara, CA
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    Monte
    #5 Monteman, Jul 7, 2011
    There is a really good thread about the risks of back flow in the exhaust system at lower RPM's if the bypass is wired open It was done by the guys from Capristo and had enough actual data points (not opinion) to convince me it is a bad thing.
     
  6. skierlawyer

    skierlawyer Formula Junior

    Sep 12, 2010
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    #6 skierlawyer, Jul 7, 2011
    I think I will leave the exhaust bypass alone. I am probably going to put the gutted cats on though. The car sounded much better this way. Any risks with this? I would think it would lower the engine bay temp and be better if anything...
     
  7. pourquoi_ne

    pourquoi_ne Karting

    Mar 16, 2006
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    England
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    #7 pourquoi_ne, Jul 8, 2011
    Last edited: Jul 8, 2011
    The problem is:- in order to gut the Y-pipe cats you have to remove the heatshield and fibre cloth from around the pipe. That means that there will be no heat insulation and your lower engine bay temparature idea will not happen. I had my pipe ceramic coated to compensate. I'm not sure the whole operation was worth it, quite honestly! I obviously have too much spare time on my hands!

    PS You are probably talking about the main cats, I guess so my comments above are not too relevant - sorry!
     
  8. pourquoi_ne

    pourquoi_ne Karting

    Mar 16, 2006
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    #8 pourquoi_ne, Jul 8, 2011
    I bought a second hand one in here in the UK for £100, gutted it, fitted it to my car then sold mine for £130!
     
  9. Rob'Z

    Rob'Z Formula 3

    Mar 29, 2008
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    Tucson,AZ
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    Robert
    #9 Rob'Z, Jul 8, 2011
    FWIW, I did some tests of my own on my car with a wired open bypass valve. I did the 'paper test' holding a piece of paper across both passenger side exhaust tips and had my friend rev slowly through from idle to about 6000.......the paper never tried to 'stick' to either tip, it was always pushed away.

    I ran my car on a dyno and sampled the air/fuel mixture from both inside and outside tips, neither ever had a lean reading indicating fresh air was passing the sensor.

    This was done on a '97 with stock ungutted cats and stock ungutted Y-pipe with a Mille Miglia muffler.



    Rob
     
  10. skierlawyer

    skierlawyer Formula Junior

    Sep 12, 2010
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    Brian
    #10 skierlawyer, Jul 8, 2011
    Thanks Rob, great info.

    I live just outside Denver, where its usually sunny, and its rained every day since I took the car home. I went for a drive today for some petrol therapy with the top down and within 1/4 mile, the sky started to open and light rain, I pulled into the nearest lot and put the top back on, and continued my drive to and up through a beautiful canyon. I took it easy on the car because of the wet, I can't wait to really wail on it on a nice day. I think early morning will be my best bet...

    Going to put the gutted cats on asap!
     

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