Performance is all about pushing the envelope. As camshafts become more aggressive in the search for more power, these lobes make life increasingly difficult for valvesprings. This may seem like a problem only for drag racers spinning stratospheric-rpm small-blocks, but this situation applies even to everyday street engines. Valve float and loss of valve control can happen even at conservative engine speeds.
Mass HysteriaThe valvespring's only job is to control the valve. This means that the valve should open and close only when the camshaft signals the valve to do so. Roller cams drastically increase acceleration rates, especially compared to flat-tappet lifters, which means that the valvespring must now control a mass that is now moving much quicker at the same rpm. That might seem like a simple thing, but keep in mind that the rocker-arm ratio also multiplies the acceleration rate of the valve. On the opening side of the lobe, the valve accelerates up to its greatest speed and then must start decelerating back to zero velocity at maximum valve lift. Then, the valve must begin to close, accelerating up to a given speed and then back to zero again as the valve closes. All of this has to happen very quickly, especially at high rpm.
All of this sounds fairly simple-and for stock engines, it is. But as we add variables like increased valvetrain weight and engine speed, the situation changes drastically. As engine speed increases, the valve must open and close in a shorter period of time. What is easily accomplished at 3,000 rpm must be completed in half the time at 6,000 rpm. At 6,000 rpm, an intake valve must open and close 50 times a second! Again, if the valvespring is designed, installed, and used properly, this is usually not a problem. But consider what happens when we add weight into this equation with a larger valve. Simple physics tells us that heavier objects require more force to accelerate, just like a heavier car requires more horsepower to accelerate. Adding larger valves means the valvespring must control additional weight, more than likely at higher engine speeds.
Here's the rub. Bump the valvespring pressure up to increase control, and that additional load pushes down on that little piston inside the hydraulic lifter. At higher engine speeds, the acceleration loads are so great that the lifter is no longer able to maintain the oil in the lifter cavity, pumping the lifter down. This creates excessive lash and lost valve lift that quickly kills power. So, there is a limit to the amount of valvespring pressure we can apply to control this heavy valvetrain. Of course, we could bolt in a new mechanical roller camshaft, but that's an expensive solution. Since we can't increase the spring load with a hydraulic lifter, the more elegant solution is to reduce valvetrain weight.
Weight WatchersRacing-engine builders have known for decades that lighter valvetrain components allow higher engine speeds without loss of valve control. The key is to reduce weight on the valve side of the rocker arm, because the rocker multiplies the lobe acceleration rate by the rocker ratio. This is the idea behind titanium retainers, valvesprings, and ultra-lightweight titanium valves. All of these are excellent ways to reduce the mass of the valvetrain that must be accelerated, but they are also very expensive, and for the most part, race-only solutions. But let us consider the valvespring itself.
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