When you get right down to it, all the valvespring essentially does is pull the valve closed after the cam has pushed it open. Unfortunately, if that is all you care about when it comes to valvesprings, then you are on a quick road to broken parts and poor finishes.
Valvesprings are among the most stressed parts on any race engine. They have to be strong enough to handle extreme cam lift characteristics at high rpm, yet light enough to reduce the amount of mass in the valvetrain. They are constantly pushed to the limits of valve float (and often beyond it) in the search for more rpm. They live in an environment of extreme heat. And to top it off, there are 16 of them in your race engine, so you can multiply the probability of a broken spring ending your night early by that factor right there.
Fortunately, the technology behind valvesprings has made great advancements in the last 10 years, and the possibility of a broken spring is actually quite low if they are correctly installed and monitored. Part of that responsibility falls on your engine builder, but much of it, for example monitoring your springs, falls on you. This is especially true if you are racing a stock engine or plan to change out your own springs.
It's All About PressureAs we mentioned, the spring's role in the engine is to close the valve. More truthfully, the spring has to keep the entire valvetrain connected so that the valve (either intake or exhaust) closes at the rate determined by the back side of the cam lobe. This means it has to be strong enough to keep the valve from lofting, or continuing to open past the point where the lifter reaches the crown of the cam lobe. If the valve continues to open because of its own momentum, it creates a break in the valvetrain. A healthy valvetrain is one in which all the components are in continuous contact. When they aren't and the valve separates from the end of the rocker, the spring eventually regains control and sends the valve crashing back into the seat and rocker, sending a shockwave through the system. Too much of this ends in broken parts. You have to make sure you have enough spring pressure when the valve is fully open (the spring is at its greatest compression). This is referred to as pressure over the nose.
If you've heard the phrase over the nose, then you've probably also heard of pressure on the seat. This is the amount of pressure that the spring is exerting on the valve when it is fully closed. A valvespring should never be in a totally relaxed state. Instead, it should always exert some pressure on the valve, even when the lifter is on the base circle of the cam for that valve. This is necessary to keep the valve seated tightly against the head to promote a good seal as well as eliminate valve bounce. Bounce is the tendency of the valve to rebound or bounce back up off the seat after it closes. This can become a problem at high rpm, so the faster the motor, the more seat pressure you are normally going to need.
Finding the right mix between spring pressures is one way an engine builder earns his keep. Too little spring pressure results in poor valve control and limits engine rpm. Too much pressure causes the pushrods to flex and shortens camshaft and lifter life. One important factor to remember if you're running a stock class is that high seat pressures can pull pressed-in rocker studs from the head. If the rule book allows you to use screw-in studs, this is always a good idea for a racing engine.
Installation and Coil BindA spring's seat pressure is adjustable by how much it is compressed between the spring seat on the cylinder head and the bottom of the spring retainer, which is attached to the top of the valve stem. This is called the installed height and is critical to proper valvetrain geometry. Increasing the installed height reduces the seat pressure, and to an extent the open pressure.
Normally, increasing the installed height cannot be done by switching to valves with longer stems because this can lead to rocker arm alignment problems (and also adds mass to the system). Better options for increasing the installed height are to cut into the spring seat in the head, which requires a qualified cylinder head machinist, or offset valve locks, which raise the retainer height.
Lowering the installed height is good for increasing the seat pressure, and the opposite steps are usually taken. Instead of cutting into the spring seat, you can add shims underneath the spring. Offset valve locks that lower the retainer are also available.
Be careful when reducing installed height if you are trying to raise the spring's open pressure. Increasing the seat pressure too much can lead to durability problems; plus, reducing the installed height too much can cause coil bind issues.
Finally, once you have determined the correct installed height, always use extreme care when installing and removing valvesprings. Never use another metal object to pry or otherwise manipulate a spring. "Any time you use metal on a spring, such as a screwdriver if you are trying to remove an inner spring, you run the risk of scratching the surface," explains Billy Godbold of Comp Cams. "That's a bad idea, because that will introduce inclusions on the surface of the spring, which creates a weakened area. Keep Popsicle sticks or something on hand. As a general rule, never stick anything in a spring that you wouldn't stick up your nose or in your ear."
Coil BindNo matter what size the spring, there is a limit to how much the spring can compress before the coils begin to touch, and the spring can be compressed no further. When it comes to valvesprings, coil bind over an extended period can be disastrous.
"As a general rule, you want at least 0.060 inch of travel in the spring over maximum valve lift," explains Allen Bechtloff of Crane Cams. "On the extreme end of the spectrum, some Cup teams are actually setting up their springs to bind at the very end of the lift. They do this because when a spring binds up, it dampens the harmonic wave traveling through it. But this is not something everybody should do. These Cup teams have done a lot of work on the spintron and know exactly how far they can push things. They are aware of the extra wear this puts on parts and can afford to replace parts regularly to avoid a failure."
The difference between the installed height of the spring and the coil bind height (plus 0.060) is the spring's working travel. This travel needs to be just slightly larger than the total lift for the corresponding valve. When calculating valve lift, don't just look at the cam spec card and the lift numbers. That number is multiplied by the ratio of the rocker arm to get the valve's total lift. For example, if you are running a camshaft with an intake lobe lift of 0.400, along with 1.7:1 ratio rocker arms, the max valve lift is 0.400 x 1.7, or 0.680 inch.
As a general rule, you want no more working spring travel than you need. If you have more than you need, switch to valves with shorter stems-if it won't screw up the rocker arm geometry-to shorten the installed height. This will also help keep your springs in the correct operating pressure range.
Weighty MattersNow that we've got the mechanics out of the way, it's time to move on to other factors that affect a valvespring's performance. One of the greatest concerns with any racing valvetrain is the total mass of the system. It may at first seem counterintuitive, but a lighter system can be more durable and work better than heavier components.
"Spring mass is kind of like feedback," says Godbold. "A heavier spring means more load on the system. Then you need more pressure to control the additional mass of the spring. But if you do the opposite, the result can be exactly the same thing. The more mass you take off the spring, the less load you need to control the valvetrain. So, if the required loading is less, the spring doesn't need to weigh as much to give you the pressure you require."
Chasing weight has led to a change in philosophy among many engine builders and component manufacturers. A perfect example is Comp Cams' new beehive valvesprings. Instead of heavy, double springs which have become the norm in racing, the beehive spring is designed to cut the most weight possible. The beehive design uses a single spring, cutting the weight of an inner spring as well as a metal separator. Its top coil also has a considerably smaller diameter than a conventional, cylindrical spring. That smaller diameter means a smaller retainer is used to hold it in place, cutting more weight. So, in a properly designed system, a single beehive spring with its lower spring pressures can do the same work as a heavier double spring with higher spring pressures.
Even if you are using a more conventional spring, you should consider the spring's mass when making your selection. Advancing technologies in manufacturing have enabled single-spring designs that are stronger than ever.
"If you are running a class that requires stock-style hydraulic lifters, you should be fine with a good single-spring design," says John Steely of Howards Cams. "Unless you are running extremely aggressive ramp profiles on your cam, a single spring will do the job while limiting weight. The one exception I can think of is a class that has valve lift limitations. In that situation, you normally run a cam that opens and closes the valve quickly and has a flat nose to hold it open and close to max lift for as long as possible. That design can be hard on springs, and you might need a double spring for that."
Steely adds that there is a large overlap in pressure between single- and double-spring designs. The choice is up to the engine builder.
Heat"We've done extensive testing with spintron machines, and it is amazing how much heat a spring can generate on its own," says Bechtloff. "Besides the radiant heat an engine generates from the combustion process, the heat a spring generates internally can be very damaging to the metal."
When it comes to cooling springs, there is nothing better than a continuous flow of good ol' engine oil. On high-end, dry-sump systems, this is best accomplished with dedicated spray bars in the valve covers that direct a mist of oil at the springs. That isn't feasible-or normally legal-in lower classes that require wet-sump oiling systems, in which case the best thing to do is simply not restrict oil to the heads. Do whatever you can to limit the oil from dripping down onto the crankshaft, but do not limit the amount of oil that can get to the springs.
Synthetic oil is also a good idea. Although it doesn't pull heat from metal any better than mineral-based oil, synthetic lubricants do not break down as easily when subjected to heat. This means that in high-heat environments, it can do its job better, longer.
If you are required to run a stock-type valvetrain, another option is Crane Cams' Kool Nut. Designed as an oversized rocker arm nut, the Kool Nut acts as a heat sink and also directs oil from the pushrod onto the fulcrum of the rocker arm, which is an extremely high-temperature area.
Record Keeping"The strongest mind can't hold information like the weakest ink," Godbold says of monitoring your valvesprings' performance. He's talking about record keeping, and he's absolutely right that a simple notepad and ink pen can be among the most valuable tools at your disposal.
"Get yourself one of those pull-down spring checkers," he continues. "Check at least four different springs in four different places, and write it down in your log book. After your first race or warm-up, check those cylinders and write down your findings in your logbook. Continue that every time you run the car.
"What you should see is an immediate drop-off, a plateau, and then another drop-off in pressure after a period of use. As soon as you see your springs on that second drop-off change them immediately, because after the springs reach the end of that plateau they will start breaking. If you keep on top of it, you can just about eliminate spring failures during competition, but you have to be vigilant."