DaveKillens wrote:The more revs you ask of the engine, the stronger the spring has to be, so that it pushes the valve back up in time before the piston gets there and makes contact. For a steel (or any metal) wound spring, the further it compresses, it also resists. So if the first millimeter requires 500 Kg of force, it may require even more force too move it the next millimeter, and so on and so on. This requires a lot of force, making the cam and cam drive gear work much harder. And not only that, each compression and relaxation cycle generates a lot of heat. In NASCAR, where they have to run coil springs for the large valves they run almost red hot, they have to receive a constant bath of cooling oil or the valve spring would fail very quickly. And of course, the valve spring itself has mass, which resists the returning force., Inertia.
So the pneumatic system has a lot less mass, generates a lot less heat, does not ask the cam to push as hard to get equivalent valve lift, and returns the valve to the closed position much quicker than coil springs. All advantages in the racing world, but impractical in the real day to day world because if your valve system lost pressure overnight, when you tried to start your engine, all you would hear was all the valves making ugly contact with the pistons.
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