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Thread: Double Frame Rail car

  1. #1
    Junior Member SHOW GUEST
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    Double Frame Rail car

    I have been told that a double frame rail car "eats 150 HP" and will not work well with a small block setup. Any truth in this ? ? ?

    (I am looking for a new car for a 1400 HP Nitrous small block / Glide combination.)

  2. #2
    Senior Member DYNO OPERATOR
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    Double

    I had a double rail car door and it was faster after I cut the top rail for more flex. That was with 900 HP with PG.

    There are different types of double rails. There are angle bars from the top of the 4 link down to the trans mount to the full rail going all the way to the front motor plate.

    Pro Stock cars have them and 1400 HP is enough to consider at least a partial double rail, whether small block or big block, even with PG.

  3. #3
    Senior Member DYNO OPERATOR
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    What?

    That is a little funny that someone might believe that the stiffness of a frame would cost horsepower. If the car were heavier due to excessive tubing for the job, then there would be some weight savings in not having the extra tubing. I would go with the double frame rail for any car application that could afford the small additional 30 to 40 pounds it could possibly weigh maximum, if chromoly.
    Bruce

  4. #4
    Senior Member DYNO OPERATOR
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    I always thought that a chassis should be rigid and let the suspension do it's job?

    TS1955

  5. #5
    Senior Member RACING JUNKIE TheYellaBrick's Avatar
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    IMHO ...... and observations....
    Door cars have different requirements than rails. They NEED to be as stiff a platform as possible in order to tune the suspension.
    Rails need SOME flexibility to take up the shock load as they are sooo much lighter and hit the tires harder.
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  6. #6
    Senior Member DYNO OPERATOR
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    Flex bad, Double Frame good

    I believe that the above comments are correct in there assumption. The frame can not be flexible in a drag car and be tunable. The result of a flexing frame is that the frame acts as a spring, not allowing the purposeful spring rate that was installed to work as it should. Also the shocks only act at they are acted upon, therefore if the frame that they are fastened to is moving with the shock or flexing, then the dampening force of the shock will not be controlling the wheel it is fastened to. The rear suspension mounts (4 link or ladder bar etc.) that the inner frame rails are fastened to can not move independent of the four suspension mounts. The movement or flex in this area will not allow controlled pre-loading of the suspension and can effect consistancy and traction when conditions change at the track. This flexing condition is why I always use the double frame rail in my own race cars. The only time the inner frame rails are difficult is when the chassis is very narrow and leaves little room for the driver to clear the funny car cage, but is always possible, just more challenging.
    Flex (eats) horsepower because the force is not directly applied to forward motion and does not apply an equal opposite force when the chassis returns to the pre flex position. The energy is used in bending and lifting the frame so some of that energy is not returned to forward motion applied the suspension.
    Bruce

  7. #7
    Senior Member RACING JUNKIE TheYellaBrick's Avatar
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    Re: Flex bad, Double Frame good

    Quote Originally Posted by TopspeedLowet
    The energy is used in bending and lifting the frame so some of that energy is not returned to forward motion applied the suspension.
    Bruce
    The above applies to forward motion eating wheelies, as well.
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  8. Racing Junk


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