There’s no doubt that the control center of any engine is its valvetrain. The camshaft, lifters, pushrods, rocker arms, and valvesprings all have to work in perfect unison in order to open the valves the correct amount, for the correct amount of time, at the correct time in the operating cycle of the engine.
While there has been an incalculable amount of time and money spent in the past half-century trying to enhance the precision of valve events by minimizing deflection and maximizing control of the valvetrain, one of the easiest places to look within the average combination are the valvesprings. Getting the right spring doesn’t have to be rocket science (unless you’re doing something off-the-wall or way outside of the norm).
Erson Cams put together the above video as a way to walk you through the Rules To Remember when selecting valvesprings. In it, they also take some of the mystery out of the little coils under your valve cover that keep your engine’s valvetrain in check, while conveying that there are many more factors to choosing the correct valvespring than just the spring rate. However, for the most part, spring rate is the main factor of a spring and, much like the story of Goldilocks, too much or too little spring rate can cost you power, or even broken parts.
First, we need to define what exactly your valvesprings do. Not only do they return the valve to a closed position once opened, but they also keep the valve in contact with the rocker arm, which in turn stays in contact with the pushrod, which stays in contact with the lifter, which stays in contact with the cam lobe itself. If any of those parts becomes unloaded, it is no longer transmitting the camshaft motion into valve motion.
The first factor that needs to be taken into consideration when selecting a valvespring is the amount of valve lift. This might seem simple enough, but in order to properly establish variables down the line, the total amount of valve travel will need to be known. Erson points out that most engine builders aim for the valve’s maximum lift to fall within .050 to .060 inch from coil bind (the point where the spring can no longer compress because the coils are physically touching).
The second factor is engine RPM. As engine speed increases, so do inertial loads (valve speed plays an exponential factor in the force exerted on the spring), as well as creating harmonic resonances. This can all be factored into the spring when designing it and is part of the reason builders shoot for a specific distance from coil bind. This allows for complete compression of the spring, while not allowing excess distance between coils when the valve is closed, which could allow harmonics to run rampant.
The third factor taken into consideration is knowing the aggressiveness of the camshaft lobe. A lobe that gently moves the valve off the seat to max lift can have a lighter valvespring than one that has to deal with an aggressive ramp rate, yanking the valve off the seat violently. On the other side of the valve’s travel, too light of spring on an aggressive return to the seat can cause a loss of control, which is bad for power and hard on parts.
Loss Of Control
Losing control of your valvetrain can have a wide variety of results, ranging from a simple loss of power to near-immediate parts destruction. Even the mildest instances of loss-of-valvetrain-control are bad for the longevity of the engine, as it accelerates component wear. To clarify, there are two types of typical loss-of-control — valve loft and valve bounce, which can both be referred to as valve float.
Valve Loft occurs when there is not enough spring pressure as the cam swings through peak lift, and the lifter is separated from the camshaft until the spring catches up with the rest of the valvetrain. Loft is caused by insufficient open pressure.
Valve Bounce occurs when the valve meets the seat with more force than the spring has, allowing the valve to come off the seat and open briefly when it should be closed. Bounce is caused by insufficient seat pressure.
Valvesprings come in a number of different designs, the most easily identifiable of which is the number of coil springs in the assembly. Single springs are, as the name suggests, a single coil of wire. A double-coil has one smaller coil spring nested inside of a larger coil’s I.D. A triple-coil spring is, you guessed it, three coil springs looking like a Russian Matryoshka doll, all nestled inside one another.
The parameters described above will dictate the valvespring load required to maintain control of the valve throughout the operating range. Once that is decided, how you achieve that load is where the different spring types come into play. Each design comes with different characteristics that allow it to exert the force required, in a manner which best corresponds to your engine’s needs.
As a general guideline, Erson recommends that for a flat-tappet camshaft, a seat load of between 120 and 140 pounds of pressure. For Hydraulic roller lifters, 160 pounds of valve seat pressure from a single or double valvespring is the recommended starting point. Moving into solid roller territory, loads start to increase significantly, as Erson recommends between 200 and 400 pounds on the seat, from a double- or triple-coil valvespring.
While far from an end-all-be-all guide on valvespring selection, this video should at least make you more comfortable with the options available when looking at a potential valvespring for your combination.