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On old, very low-speed engines, you may find no valve springs at all. Air opens and closes the valve. The main job of the valve springs is to avoid "float" -they overcome the inertia of the valve and lifter and keep them in contact with the cam as they start to close. That force goes up as the square of speed, so it pays to avoid high revs. If you are going to lower the red-line, a cam with less dwell and overlap is better, as there is less inertia in the manifold gasses.
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