Engine response time - deceleration | FerrariChat

Engine response time - deceleration

Discussion in '206/246' started by jselevan, Jan 27, 2009.

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  1. jselevan

    jselevan Formula 3

    Nov 2, 2003
    1,873
    #1 jselevan, Jan 27, 2009
    What factors might cause the Dino engine to take its time when returning to idle? Assuming that the throttle linkage is not the culprit, and short of lightening the flywheel and pressure plate, is there a way to improve response? When shifting, it seems as though it takes a long time for the engine speed to drop, thereby forcing the driver to hesitate before engaging the next gear and releasing the clutch.

    Is this a timing issue? That is, will advanced or retarded timing lead to this symptom in the absence of other traditional timing symptoms (back firing, missing, lack of power, etc.)? I assume that my butterflys are closing and that the linkage is set correctly (I have paid great attention to this).

    All thoughts are welcome.

    Jim S.
     
  2. tx246

    tx246 F1 Veteran
    Owner Rossa Subscribed

    Nov 4, 2003
    6,472
    Texas
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    Shawn
    #2 tx246, Jan 27, 2009
    most likely not the problem you are having, but the drivers carpet sliding into the throttle will cause a similar problem.
     
  3. daviekj

    daviekj Formula Junior
    Silver Subscribed

    May 9, 2008
    465
    UK
    #3 daviekj, Jan 27, 2009
    Jim, I expect you have checked this. Are the distributor weights sticking on return. ie. timing staying too advance for the revs as they drop? I played with some new replacement weights and could feel the damping pistons catching as they returned. I am a little doubtful that this is the cause, but all I can think of.
    Stonger return spring to take up any slack in throttle cable?
    Kevin
     
  4. jselevan

    jselevan Formula 3

    Nov 2, 2003
    1,873
    #4 jselevan, Jan 27, 2009
    TX246 and Kevin - both good thoughts. The carpet has been adjusted to eliminate the possibility. Kevin, your comment suggests that advanced timing could lead to the symptom. Is it advanced timing (static), or is it failure to revert to the designed timing curve after reving that is the culprit?

    It is a bit of a pain to remove the distributor and check all this. However, when I rebuilt the car several years ago (3,000 kilometers), I rebuilt the distributor with new bearing, and cleaned and lubricated the advance mechanism.

    Has anyone else noted this symptom? It may be the normal response dynamic for the engine.

    Jim S.
     
  5. John Corbani

    John Corbani Formula 3
    Honorary Owner

    May 5, 2005
    1,153
    Santa Barbara, CA
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    John Corbani
    #5 John Corbani, Jan 28, 2009
    Jim,
    My engine has always been slow on deceleration. Have had the distributor apart so many times that I don't think that that is the problem. Carbs are fine, they close NOW. My immediate comparison on buying the car was an Alfa 1600 full Veloce. The Alfa was faster at decel and had some torque off the line. The Dino has nothing below 3,000 rpm. I think it has something to do with the cams and a relatively heavy flywheel. The transfer gears and all the gearbox gears are part of the flywheel mass as long as the clutch is engaged. An inline engine-gearbox should be faster. Napolis seems like the person to ask. He has both a Fiat Dino and I believe an inline setup on his new Dino.
    John
     
  6. daviekj

    daviekj Formula Junior
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    May 9, 2008
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    UK
    #6 daviekj, Jan 28, 2009
    Jim, The degree of slow deceleration that you are experiencing is obviously difficult to judge without feeling the car. I don't remember experiencing any anomolous effect in mine, but may be I havn't thought about it. My suggestion was a long shot in the absence of any other reasonable logic I could come up with. I agree its unlikely. None the less, this is what I was trying to suggest:

    A few degrees of advance is enough to make a noticeable increase in engine speed, especially at lower rpm. I know this simply form playing with the dynamic timing and logic. Prior to gear change, the distributor is rotating at medium to high rpm and the advance weights are extended. During a gear change, the throttle is only momentarily closed, so fuel vapour will be entering the cylinders. If the advance weights are not retracting appropriately, then the mixture ignites too far advance for the rpm. I think this could slow the deceleration. This is purely a weak guess.

    Kevin
     
  7. jselevan

    jselevan Formula 3

    Nov 2, 2003
    1,873
    #7 jselevan, Jan 28, 2009
    John and Kevin - I suspect that my engine response dynamic is normal for the car, and that I am simply aware of it as I shift. I have two Dinos, and while I drive one most of the time, the other seems to have the same symptom. I was just wondering if others had noticed this, and if there was an easy fix.

    Perhaps I am influenced by one of the first articles in a Auto magazine that described the Porsche Carrerra GT. The author noted, with particular emphasis, the instant response time of the engine...it revved up and down without delay.

    Jim S.
     
  8. TonyL

    TonyL F1 Rookie

    Sep 27, 2007
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    Norfolk - UK
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    Tony
    #8 TonyL, Jan 29, 2009
    First thought air/ vac leak from the o ring manifold

    second sticking bob weights

    Third are the carbs really shutting off. Make sure that the accelerator arm is not touching the plastic cam at idle;
    remedy is simple tweak out the actuating arm so there's about 10 thou gap otherwise it will be squirting fuel constantly.

    Tony
     

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