Conical Valvesprings – The Story Behind The Coils

Jeff Smith Aug 26, 2014 0 Comment(s)
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The scenario goes something like this. Our LS3 used to rev freely and make power all the way up through 6,800 rpm, but now it struggles to get to 6,000 and power is definitely down. After a thorough engine diagnosis, we've narrowed it down to weak valvesprings. In the past, the classic fix was to just hit this package with a bigger hammer in the form of big, dual valvesprings. But perhaps there is a better way. Engine builders whose engines routinely spend time in the rpm stratosphere have long known that reducing weight in the valvetrain, especially on the valve side of the rocker arm, is an excellent way to stabilize valvetrain dynamics.

COMP Cams knows this and several years ago introduced the beehive spring. This was the first attempt at reducing valvetrain weight by coiling the top of the spring to a smaller diameter, which creates a much smaller diameter spring retainer. This worked but had limited benefits. An even better solution came from deep in the past. As long ago as the 1920s, engineers knew that creating a tapered, or pure conical, spring was beneficial, but the metallurgy and machining techniques could not deliver on the idea. Today, high-quality spring wire and CNC coil winding machines make this possible even for street engines.

Before we get into the specific benefits of the conical spring, let's look at how a conventional, cylindrical coil spring operates in an engine. If you've ever watched a high-speed video of a conventional dual valvespring at rpm, the video radically slows the valve action so that we can see what's really happening. After the valve completes its lift cycle and closes, there is a vibration wave that travels through the spring. Each coil vibrates slightly and passes this vibration to its neighbor. This wave is caused by the inertia of the mass of the valve and spring hitting the seat at high speed. It looks just like a wave in a pond after you've dropped a rock into the water. COMP Cams' cam designer and resident astrophysicist Billy Godbold describes the wave in the spring this way "It's as if you had a cylinder of Jello and whacked the top of it with a spoon. It gets all wiggly."

Conical Springs Comparison 2/10

The best way to illustrate the conical spring concept is through comparison. On the far left is COMP’s traditional PN 26925 dual spring. In the center is a beehive spring for a 6.0L LS engine, while on the far right is COMP’s new PN 7230 conical spring.

Conical Spring 3/10

The conical spring is not only progressively wound tighter as it nears the top, but the spring also varies the spacing between the coils to enhance its natural damping effect.

Godbold also says the spring sees this wave literally just like another valve lift cycle in terms of stress imposed on each individual coil in the spring. If this is a traditional, cylindrical valvespring, each coil in the middle of the spring is exactly like its neighbors in terms of diameter and spacing. Each coil also has a natural frequency. This is important to remember when we compare it to the performance of a conical spring. Because all the middle coils on a conventional spring are the same, they react to input (lift) the same way. The wave has a frequency that is determined by a combination of factors that include the diameter of the wire, the uniform spacing of the coils, and the spring's overall diameter. To improve valvespring performance and durability, this wave action must be damped. That's where coil spring dampers come into play.

Single springs generally use a flat wire damper that is designed to press against the wire coils and damp this frequency (the wave) that travels through the spring. This is also part of the function of inner springs on dual valvesprings. The inner spring is designed to rub against the inner portion of the outer spring to damp these wave motions, but it is only partially successful. The problem with this rubbing action is that it creates friction, heat, and wear. Plus, when any coil spring is compressed, the stress on the wire is concentrated on the inner diameter of the spring. So when we introduce a dual spring, whose job is to create an interference fit between the inner and outer spring, it rubs on the most highly stressed portion of the main spring! It's obvious that if you could design a spring that would naturally damp this wave action without the negative aspects of a damper, you would have a superior valvespring. That's the conical spring.

Progressively reducing the diameter of the spring from the very bottom coil all the way to the top creates multiple advantages. First and foremost, each coil now has its own frequency that is different from its neighbor. This does not completely eliminate the wave that is created when the valve hits the seat, but the spring now has natural damping, which drastically reduces the wave's amplitude (load). This is important because Godbold told us that when COMP subjected the conical spring to long-term, high-speed durability testing on the company's Spintron, they witnessed minimal reduction in load compared to a traditional dual spring. Remember earlier we mentioned that each wave action in a traditional coil spring subjects the spring to the same stress levels as a normal valve lift cycle. By reducing the amplitude of the wave in a conical spring, this reduces the stress on the spring—so it lasts longer. If you look at COMP's graph of the difference in oscillation reduction at 7,000 rpm, the difference in the amount of load (stress) imparted to the spring after the valve closes is the reduction in amplitude—the difference between the red and blue lines.

Another way to damp this natural wave action is to vary the spacing of each coil of wire. If you look closely at a side view of the COMP conical spring, you can see that starting from the bottom, the spacing between the coils is progressively reduced. This also helps to damp the natural frequency of the spring. When the diameter and spacing of coils are combined, the spring becomes its own natural damper.

Oscillation Reduction Graph Data 4/10
Single Wire Springs 5/10

Almost all performance single wire, cylindrical springs will use a flat wire damper like this one to help control spring vibrations. Its interference fit damps spring frequency but also causes friction and heat between the damper and the spring.

Dual Spring 6/10

A cylindrical dual spring like this PN 26925 is currently a popular performance spring. The inner spring increases load and also act as a damper. This has been the traditional (but not the best) way to damp spring movement.

Conical Spring Retainers 7/10

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