400 dwell angle | FerrariChat

400 dwell angle

Discussion in '365 GT4 2+2/400/412' started by simonc, May 3, 2015.

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  1. simonc

    simonc Formula Junior

    Nov 1, 2003
    882
    Herfordshire, UK
    Full Name:
    Simon Campbell
    Does anyone know what the dwell angle should be for a 400 carb engine. This, of course, has the two distributors with one set of points in each distributor operated by a six lobe cam. I have rebuilt the distributors (new bearings, cleaned and greased the weights, new points, new condensers etc.) but I can't find any reference to the correct dwell angel anywhere. I have set teh points gap to 0.35mm and testing the dwell angle on the bench shows that this is 30 degrees on both distributors but I do not know if this is correct or not.
     
  2. samsaprunoff

    samsaprunoff F1 Rookie
    Silver Subscribed

    Jun 8, 2004
    4,160
    Edmonton, AB Canada
    Full Name:
    Sam Saprunoff
    #2 samsaprunoff, May 4, 2015
    Last edited by a moderator: Sep 7, 2017
    Good day Simon,

    I do not know the dwell angle, but according to the 400 GT owner's manual you look pretty bang on... assuming your 30 degree is the advance at 5000 RPM. Attached are images from the manual.

    Cheers,

    Sam
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  3. simonc

    simonc Formula Junior

    Nov 1, 2003
    882
    Herfordshire, UK
    Full Name:
    Simon Campbell
    Thanks Sam but I was talking about dwell angle when I said 30 degrees not ignition timing. Dwell angle is the angular rotation that the distributor shaft moves through between the points opening and closing again. When we set the points gap what you are really doing is altering this dwell angle and it the dwell angle that is the important measurement as it sets the time that the coil has to 'recover' between charges.

    I have the owner's manual and it is not shown in this. I have the WSM the 400i and Daytona but the 400i has a single distributor without contact breakers and the Daytona has twin sets of points inside each of it's two distributors so it's dwell angle is different as each distributor shaft has three lobes rather the six lobes the 400 has.
     
  4. samsaprunoff

    samsaprunoff F1 Rookie
    Silver Subscribed

    Jun 8, 2004
    4,160
    Edmonton, AB Canada
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    Sam Saprunoff
    Good day Simon,

    My apologies... I was too busy focusing on the 30 degree number as opposed to looking for the dwell angle. Since the dwell angle is a function of the point gap and that the owner's manual provides a range of 0.32mm to 0.38mm this would imply that there would also be this variance in the dwell angle... would you not agree? Given this is the case I would surmise that Ferrari deemed that this point gap range (and associated Dwell variance) is the acceptable range for the correct operation of the engine. Is there an optimum setting? Probably... but one would need to measure the amount of spark energy being produced in order to determine where this optimum setting should be:

    - setting the gap on the low side would increase the magnetic field within the primary windings of the coil and thus potentially a greater spark... but the issue here is that since the gap is smaller the points will close sooner and so there is less time for the magnetic field to collapse and thus less energy is transferred to the secondary windings and so less spark.

    -setting the gap on the wide side would reduce the time for the magnetic field to build up and thus less energy transference to secondary windings.

    Without actually measuring the secondary voltage output it would be tough to know the optimum gap setting.

    I think using the midpoint like you have done is probably the best solution.

    Cheers,

    Sam
     

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