A camshaft can be a huge performance component for an engine-many people know this. Cam lobe design is often regarded as a black art. Many who have mastered it prefer it that way to keep people from understanding what really happens in a valvetrain. To further complicate things, that lobe is only as good as the system you put it in. Yes, the system.
All of the components that make up a valvetrain system interact with each other and either work, don't work, or fall somewhere in between-most are in between. Mass plays a big part in this system. We are going to use a very basic principal of physics in this discussion to illustrate the complexities of valvetrain motion.
F = MA(Force = Mass x Acceleration)
The mass of the valve and all the reciprocating and rotating components of the valvetrain affects the forces in the system. The acceleration of the system is dictated by the lobe profile-or the rate at which the lobe moves the hydraulic lifter. We can't necessarily minimize force, because often to obtain better performance, we may intentionally accelerate things faster. The key to look for is the proper balance of component mass, stiffness, natural frequency, cam lobe acceleration, and forces experienced in the system to make it all work together.
To most accurately determine the effectiveness and stability of a valvetrain, one must test it on a valvetrain cell. One commercially available, known as the Spintron, is similar to Katech's Test Cell 1, except we use our proprietary data acquisition and data analysis programs. The cell utilizes a DC electric motor to drive a "spin buck" consisting of a block with a window in one cylinder, a dummy crankshaft (no pistons or rods), cam drive chain, and the valvetrain system. By bouncing a laser off the bottom of the valve, we can watch in real time as valvetrain components deflect under load, valves loft over the nose of the cam or bounce upon closing, and find out what impacts the stability of a system-or leads to failures. Our system measures valve lift in 0.0005-inch increments at 1 crank degree resolution up to 12,000 rpm. Valvetrain limiting speed is typically determined by the amount of valve loft at max lift or bounce on the seat during valve closing.
The question you need to be concerned about is what the limiting speed or fuss points of your system are, and are they in the normal operating range of your engine. All systems have a limit, or areas that are less than optimum. We prefer those points to be several hundred to several thousand rpm beyond redline.
Test Objective
Katech recently performed a series of tests to identify cam lobes, valvesprings and their installed heights, valves, retainers, and combinations of these parts that work well for hydraulic systems in GM Gen III and IV V-8 engines. This article will specifically address one portion of the test to understand the effect of valve mass on valvetrain dynamics by testing a hollow exhaust valve against a solid Inconel valve on an LS7 valvetrain. We tested this because many people choose solid stainless steel or Inconel valves as an "improvement" over the factory stainless steel, sodium filled, hollow-stem valve.
The objective of this article is to give the end-user a basic understanding of what is involved when putting together your particular valvetrain system. This should equip you with the right questions to ask of your particular parts supplier or engine builder.