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Question about recurve ?

Discussion in '60-Series Wagons' started by El3bolas, Mar 5, 2017.

  1. El3bolas

    El3bolas

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    Pease explain me what is the meaning of recurve the dizzy , and why we have to do it after desmog ?
    What is done to the distributor and why is needed ?
    In simple , not expert
    terms , please ..
     
  2. NeverGiveUpYota

    NeverGiveUpYota Dare me. SILVER Star

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    Lots of threads 'why recurve.' Read up.
     
  3. Output Shaft

    Output Shaft SILVER Star

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    When the EGR system is functional, it allows a small amount of exhaust gas to be sucked back into the engine while driving. The EGR is off at idle.

    Injecting some exhaust into the intake dilutes the percentage of oxygen that gets sucked into the combustion chamber since exhaust gas is devoid of oxygen (for the most part).

    An air fuel mixture that contains less oxygen burns slower and cooler. The goal of EGR is to get the combustion temperature below 1200°F (by reducing the %O2) to minimize the creation of Nitric Oxide (NOx) which is a nasty pollutant.

    Since the EGR diluted charge burns slower, the spark needs to happen earlier (more advanced) to ensure efficient combustion.

    The USA distributors on the FJ60s were all "curved" (calibrated) at the factory to match the combustion speed of an EGR mixture. The "curve" refers to the timing of the spark at different RPMs. If the timing advance vs rpms is graphed and the dots connected, the resulting representation is referred to as the "curve".

    When a distributor gets "recurved" for non EGR use, it's being modified by changing the weights & springs inside it to advance the spark more slowly or to less of a degree for non EGR use.

    When the EGR system is disconnected, the air fuel ratio contains more oxygen which will allow the charge to burn faster (and hotter). If the stock distributor is used without EGR, it's spark advance "curve" will be too advanced and the engine will pre-ignite/ping/detonate/knock at certain RPMS.
     
  4. El3bolas

    El3bolas

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    Output shaft , thans for that great explanation .... I really appreciate it .
     
  5. Cruiser Jimmy

    Cruiser Jimmy Moderator

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    I would like to add this to FAQ. Thanks OS.

    Done!!
     
    Last edited: Mar 5, 2017
  6. rrv333

    rrv333 SILVER Star

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    X2 about adding to FAQ
     
  7. ward93

    ward93

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    So is there a good guide on doing this curve?
     

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