I need some 306ci questions answered

Discussion in 'Fox 5.0 Mustang Tech' started by StangYellow, Dec 6, 2003.


  1. StangYellow

    StangYellow Founding Member

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    Some of this might not be right, but ill try my best to describe it.

    A friend of mine has a 306, with a Holley 650double pumper, X303 cam, GT-40X heads, GT-40x intake, 1.6 lifters Hedman longubes, MSD ignition/distributor. The car feels strong down low, but seems to fall flat on the tip end. We have made trips to the track and it runs high 13's with 2.2 60ft times. On paper, the car looks like a performer, but it just isnt there. Any ideas? I know the GT-40x heads come with .500 springs and the x303 lifts .542. I dont know if the springs were changed or not. Any idea on hp/tq at the flywheel for this car? Like the said, the car is real stout down low and runs perfectly fine, it just doesnt seem to have the consistent top end power to run a lower ET.

    Thanks :nice:
     
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  2. BlackFox5.0

    BlackFox5.0 Founding Member

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    maybe it's the cam, my car starts to loose power after around 5500RPMs, andi can really feel it, the engine is screaming and it stops pulling....I think it's my cam
     
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  3. SynMan5.0

    SynMan5.0 New Member

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    What MPH did the car trap? Did he have it tuned? I would think it could be any number of things.
     
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  4. TIMMY2734

    TIMMY2734 Founding Member

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    doesnt answer your question, but what kind of intake is on there? There is no gt-40x for a carb application that im aware of
     
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  5. StangYellow

    StangYellow Founding Member

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    The car trapped 100 or 101. It has 3.73 gears. The car does throw some black smoke though at high rpm (gas) I think the carb is just running too rich.
     
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  6. StangYellow

    StangYellow Founding Member

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    sorry, its an Edelbrock Performer intake.

    (excuse me, i drive a car that requires 2 cams. I mix up a few 5.0 parts)
     
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  7. TIMMY2734

    TIMMY2734 Founding Member

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    trap speeds seem low for what he has.

    like synman said, it could be a number of things. Hes definitely got the parts and potential to be quicker than what he has now. Id start out small, and go over everything. all little BS stuff. Are the valves floating? do you have any idea of the springs?
     
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  8. SynMan5.0

    SynMan5.0 New Member

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    Timing? :shrug:
     
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  9. StangYellow

    StangYellow Founding Member

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    no idea whats up with the springs, or how strong they are. Although that would be a good thing to find out.

    I believe the timing is at 13degrees
     
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  10. OutLawSE

    OutLawSE Founding Member

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    I would check the springs. Sounds to me like they are floating on top end.
     
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  11. PURESTREET5006

    PURESTREET5006 New Member

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    In the tech line for tear down"AGAIN"
    Change your springs first of all...You said that the heads cam with .500 inch lift springs and that cam is .560 thats your first problem and then you need to check what spring pressure that cams requires(open and closed pressures)
     
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