TopspeedLowet

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