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550 exhaust pipe by-pass?

Discussion in 'Technical Q&A' started by Bab13, Aug 17, 2004.

  1. Bab13

    Bab13 Rookie

    Feb 6, 2004
    35
    Switzerland
    Full Name:
    Barnabé
    Anybody know the function of by-pass (valve) in 2 of the 4 exhaust pipes of 550 Maranello? (stock exhaust)

    Is it for noise regulation at idle? Or to create a back pression in pipes for more torque in low and medium engine revs?

    With an other exhaust system (like Tubi...), this valve doesn't exist. What is the influence in torque, below 4000 1/min for example?

    And, for the 355, is it the same function (concerning by-pass before mufflers)?

    (sorry for my chinese-english!!)
     
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  3. Thatsmytoy

    Thatsmytoy Karting

    Nov 5, 2003
    228
    San Diego, CA
    Full Name:
    Bill
    My 550 sales booklet says the by-pass valve are similar to the F50. "Greater back pressure, with the valve closed, allows the torque to be improved in average load conditions, while reduction of the back pressure at the exhaust by opening the by-pass valves enhances engine efficiency at high speeds with a full load". When I bought my 550 in April, my FSF salesman said if i wanted to rig the valves open, I would get a throatier exhaust sound at low RPM...it sounded good to me...so we did that..and its a temp rigging. The original 550 exhaust note is notoriously tame....i'm getting ready to buy the CarGraphics exhaust....my question is....do i unrig my by-pass valves when I get a new exhaust?

    Bill
     
  4. maranelloman

    maranelloman Guest


    It is for all the above. It keeps noises down at the Toyota Camry level (which is why so many 550 owners replaces the stock mufflers), and aids low RPM torque by creating more back pressure, while aiding high RPM horsepower by removing backpressure.

    But in reality, when removed & replaced with freer flowing (and sounding) mufflers, there is barely any noticeable drop in low RPM torque at all.
     
  5. AEHaas

    AEHaas Formula 3

    May 9, 2003
    1,350
    Osprey, Florida
    Full Name:
    Ali E. Haas
    There is another function. The higher back pressure at lower RPM helps keep the cats hot. This decreases emissions and helps burn unburned fuel. This increases the life expectancy of the cats and emission system from say 60,000 to 100,000 miles. Many have cat problem way too soon. This type of modification contributes to these problems. As cats foul they decrease performance.

    I liked the sound when I bypassed my cats. I then decided to find out what the long term result would be. Then I put them back the way they belong.

    aehaas
     

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