Building reliable horsepower takes matched parts, proper octane fuel, and ignition to light the fire. The focus is normally on induction, camshaft, valvetrain, and exhaust—all selected for the displacement and desired rev range.
Of all the components you’ll purchase, some will last thousands of miles or laps (at least you hope they will), while others are “wearable” items that get changed out regularly. With that in mind, valve springs often fall under the category of parts that must be changed regularly, or at minimum, checked, in a high-performance or high-rpm build.
What Do Valve Springs Do?
Valve springs have a unique job. At rest, they keep the valves shut tightly against the seats, and they are compressed as the valves to open. High pressure allows them to create a controlled motion of the valvetrain.
As you’re probably aware, cam specifications and rpm limit often dictate the stiffness of the springs. And this can change wildly based on application.
Common spring shapes are cylindrical, beehive, and conical. In addition, you’ll find dual- and triple-springs in some applications. There are a few common spring materials along with different wire size and wire shapes, too. Selecting springs is not an easy task, but we’re here to help and SummitRacing.com carries a seemingly endless list of springs for virtually all applications.
“Valve spring are just one component of the valvetrain system,” said Chris Osborn of PAC Racing Springs.
“Springs provide force to keep the valves in contact with the mating components during the valve opening, peak lift, and during closing events of the intake and exhaust cycles. The spring has to maintain that force at a rate of nearly 100 times a second, without losing any load or failing run after run. Many times, the engine speeds are limited by the ability of the springs to maintain this force, so they become an extremely critical component of any engine,” he stated.
“Valve springs are extremely high-stressed components, if not the highest stressed in the engine,” added Osborn. “They need to have specific alloys and manufacturing methods to be able to withstand the lift and rpm to which they are subject. Almost all high-performance valve springs are produced from chrome-silicon steel alloys specified in material standard ASTM A877. The valve spring wire goes through extensive levels of inspection and control to maintain cleanliness within the steel and maintain high ductility with high tensile strength. These alloys have varying amounts of silicon, vanadium, nickel, molybdenum and carbon that provide various levels of performance with tensile strengths over 300 ksi. PAC Racing Springs has developed its own alloy that has been around for years and is known as “PACaloy.” This is a specific spring material for the racing industry that optimizes the alloys with the mechanical properties to provide exceptional fatigue life with minimal load loss.”
He continued, “The lightweight nature of titanium is great for valvetrain parts, but the rapid development of the chrome-silicon steel alloys in the past decade have created a large decline in its use. Titanium is expensive with a limited lifetime and the dual-spring designs that PAC Racing pioneered over the last decade have rivaled the weight advantage of titanium with superior life with a much more advantageous cost/run factor.”
Many builders have experience selecting springs for a given combination, but if you’re taking on the job yourself, you’ll want to look at camshaft configuration, class rules, budget, and the physical room in the cylinder head. You’ll need spring with enough pressure, but not too much, and you’ll need to prevent the springs from going into coil bind.
“The first step is usually to discuss required forces with the cam designer,” said Jeff Villemure, engineer at Performance Springs, Inc. “They will take into consideration the acceleration of the cam lobe, max engine rpm, and the weight of the valvetrain. A few calculations go into determining the forces needed to control the valvetrain, but a lot has to do with history and experience.”
Osborn added, “Spring selection is not a simple process. You have to start with knowing what size spring you can fit in the cylinder head, the installed height, and valve lift. Determining the load and rate are more challenging questions to answer. Newton’s second law of motion, F=MA comes in to play since F is the spring force, M is the mass of the components (valves, retainer, rockers, pushrods, etc.) and A is the cam/valve acceleration at a given engine speed. The best starting point to determine spring loads is from cam suppliers, spring suppliers, or engine builders who have experience with all the components that go into a particular engine.”
Today, many of the top companies combine computer software, Spintron test equipment and raw experience to get you the best springs for your engine. You may have noticed that many racers have switched to beehive springs as the design has many benefits.
“Beehive springs have been around for a very long time (Wright Brothers Engine—1903) and many OEM companies use them in current engines,” said Osborn. “Anytime the mass of the valve side of the valvetrain is lighter, then the engine will have better valve control and rpm capability. The beehive spring does this by allowing the retainer to be smaller with less mass. The spring also has reduced mass on the moving end. The beehive spring essentially combines two springs into one. The conical top with the straight spring provides two different spring rates and that can also improve the ability to control the valve at high speed. Most beehive springs that PAC Racing Springs produces utilize multiarc or ovate wire that allows the use of more coils at the bottom of the spring to further enhance the damping and control with the spring.
“Beehive springs provide many great benefits; however, they are still just a single spring and can only provide so much force before the stresses become too great and a dual-spring is required. Beehive springs are great for engines that have cams with 0.600 to 0.650 inch lift with relatively lightweight valves and moderate cam profiles. PAC Racing Springs has beehive springs that can handle higher lifts, but ‘smooth’ cam lifts are required to avoid excess stress.”
The reduced diameter at the top of a beehive spring also provides greater spring-to-rocker arm clearance. Racers could consider using beehive springs for many hydraulic lifter applications. The lighter retainer weight is more important with hydraulic lifters because the spring pressure must be limited for the lifters to function and survive. With solid/mechanical lifters you can increase spring pressures significantly to control the valve movement. With solid lifters it is advisable to always err on the side of higher rather than lower spring pressures.
Valve Float/Valve Loft
The term ‘valve float’ can be misleading, as it generally is assumed to be when the valve motion at peak lift exceeds what the cam/rocker can provide. “This is what is more commonly referred to as valve loft, and lofting the valve can help make power if it’s in the right spot. But too much loft in the wrong areas can bend valves when they contact pistons. What is more detrimental is when valves close at such a high rate of speed that the valve will bounce off the seat. This is referred to as valve bounce. High levels of valve bounce can cause catastrophic problems such as broken valves, rockers, cams and springs. This is especially noticeable on a Spintron test stand. All of this is corrected with matching valvetrain component selection, especially the valve springs.”
Indicators of valve float are when an engine goes flat or stops accelerating at the upper rpm range. Or sometimes it seems to pick up a high rpm misfire. You may also see carbon residue from reversion in the intake manifold.
Coil bind is another evil that should be avoided.
As the name implies, coil bind occurs when the springs are compressed to a point that the coils jam against each other. When this occurs, the spring can no longer work properly. Knowing your valve lift, you can check the springs to make sure they can be compressed (from the installed height) to max lift, without binding.
“Springs should be compressed in a checking station or very cautiously in a bench vise to determine the exact height where all the coils touch and become solid,” explained Chris Osborn.
“It is ok to take a high-end spring and compress them solid. All PAC Racing valve springs are taken solid several times during the manufacturing and inspection process.
“This needs to be done with a retainer that compresses the inner spring as well as it may go solid before an outer spring. This coil bind height number is recorded. This is compared to the installed height and valve lift that is measured on an engine. The difference is the coil bind clearance number. This number needs to positive showing there is clearance. This clearance can be modified with shims, retainers, locks, or spring selection to tune the valvetrain for optimum performance.”
It’s also recommended that you inspect all the valve springs individually as tolerances can vary as much as 0.050 to 0.060 inch, which can be enough to cause coil bind in an individual spring.
Lastly, it’s important to inspect everything in the valvetrain for loose or broken parts, springs, spring tips. Ideally, this is done with an on-head valve spring load tester. These loads should be recorded after the engine has been broken in and then checked periodically.
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