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."
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.
Weight and Mass
Not only does the conical spring deliver inherent damping improvements, but its shape also means that it's much lighter than a conventional cylindrical spring and lighter in the right place. If you think about it, the top half of any valvespring moves a far greater distance than the bottom half of the spring. So if the top half of the spring is lighter, this makes the spring's job of controlling the mass of the moving components that much easier. Let's do some simple measurements and see what shakes out. A representative COMP dual valvespring for an LS engine would be PN 26925. Its outside diameter is 1.320 inches and it weighs 94 grams, which means the top half of the spring would weigh 47 grams. Now let's add 28 grams for a steel retainer and locks and the top half total comes to 75 grams. The COMP conical PN 7230 spring weighs 72 grams and we'll assume that the top half of it would be 36 grams even though logic dictates that it's much less than that. For the sake of expediency (and because we couldn't bring ourselves to cut one up!) we'll keep this assumption. Add the smaller steel retainer and locks at 16 grams and this totals 52 grams, which is 23 grams (almost a third) lighter than the typical dual spring.
This exercise may seem trivial except for the fact that outrageous g-forces are present in a typical performance engine valvetrain. We're talking about a reduction of accelerating mass by almost 33 percent! When you look at it this way, the effect is huge. According to Godbold, a typical small-block or LS engine at 6,000 rpm can present g-forces at the valve of between 1,000 and 2,000 g's. Much of this force is created by deflection of parts like pushrods and rocker arms that impart these huge loads on the system. With these enormous loads, a simple reduction in weight of even 23 grams at the very top of the valve is equivalent to reducing the load on the spring that has to control these forces by roughly 50 pounds, assuming 1,000 g's. If this soars to 2,000 g's, the load increases to over 100 pounds of additional force the spring must control. With the lighter valvespring and retainer, that's 50 to 100 pounds that the spring can now use to help control the valve as opposed to controlling the additional mass of the spring and retainer. Now let's reduce the weight even more by using one of COMP Cams' tool steel retainers that are roughly one-third lighter than the normal steel retainers. This removes another 4 grams, which, because of the retainer's already small size, is not a tremendous reduction, but still a step in the right direction. Taken by themselves, these changes might appear trivial, but overall with a conical spring and tool steel retainer, this makes for a lighter package that will go a long way toward creating a stable power curve.
If you want the lightest package possible, you can reduce weight by one more gram with titanium retainers—but cost may enter into this equation. The tool steel retainers are more expensive than regular steel versions but not nearly as pricey as the titanium versions. But consider this. A typical 2.00-inch intake valve for a small-block Chevy weighs 103 grams. A hollow stem version reduces valve weight by 12 grams to 91—but this weight reduction move will cost $325. A set of tool steel retainers for roughly $100 more than the stock retainers will generate the same weight savings.
Now that you know the benefits of both conical valvesprings and lightweight retainers, you have more information on which to base your next valvetrain purchases. One thing we've noticed about the evolution of valvetrain componentry is that as soon as the spring engineers create a better piece—that opens the door for the cam lobe guys to build an even more radical lobe that will push those springs a little harder. And anyone who likes making horsepower benefits from the process.
How to Determine Spring Rate
Let's say that you purchased a set of aftermarket aluminum heads but the valvesprings are a mystery. If you have access to a spring checker, you can measure seat and open load, but you might also want to know the actual spring rate. Spring rate is the amount of load that the spring applies to the valve at a given height. It only takes a little simple math to calculate spring rate. After we test the spring, it has a seat load of 200 pounds and an open load of 400 pounds at a half-inch (0.500) of valve lift. The first thing to do is subtract the seat load from the open load (400 – 200) for 200 pounds. This gives us the change in load over the valve lift of 0.500. Next, we divide this increase in spring load by the amount of valve lift to give us the spring's actual rate. So 200 divided by 0.500 equals a spring rate of 400 pounds per inch (lbs/in). Given this equation, we can solve for any variable if you know the other two. As an example, if we know the seat load and the rate, we can calculate the open valve lift load. So with a seat load of 150 pounds and a rate of 438 lbs/in, we can calculate the open load with a valve lift of 0.650 by using the formula: (rate x valve lift) + seat load.
(438 x 0.650) + 150 = 435 lbs of load at 0.650 valve lift.
Conical Spring Specs
This chart lists each of the three different COMP conical valvesprings plus a dual spring for comparison. The PN 7228 and 7230 springs are intended for (but not exclusive to) LS engine applications because of their smaller base spring diameters with two different rates. The 7230 spring is capable of accommodating up to 0.675-inch of valve lift with an open load of nearly 500 pounds. If we compare this to COMP's 26925 dual spring, the conical spring offers comparable seat pressure at a 0.100-inch taller installed height while generating nearly 80 pounds more load at a peak lift of 0.675 (495 vs. 415 lbs.). Combine these advantages with the conical's greater durability and reduced mass and you have a great combination of strength and longevity.
|Conical Spring Specs|
|Valvespring||Seat Pressure||Open Pressure||Coil Bind||Rate|
|7228 - Conical||136 @ 1.80||412 @ 1.170 (0.630 lift)||1.125||438|
|7230 - Conical||145 @ 1.90||495 @ 1.225 (0.675 lift)||1.185||520|
|7256 - Conical||160 @ 1.90||495 @ 1.225 (0.675 lift)||1.165||485|
|26925 – Dual||145 @ 1.80||415 @ 1.125 (0.675 lift)||1.1||400|
|COMP conical valvespring||7228-16||Summit Racing||$278.87|
|COMP conical valvespring||7230-16||Summit Racing||298.97|
|COMP conical valvespring||7256-16||Summit Racing||318.97|
|COMP steel retainer, 8mm valve||774-16||Summit Racing||52.97|
|COMP tool steel retainer, 7 degree, 8mm valve||1772-16||Summit Racing||149.97|
|COMP titanium retainer, 8mm valve||772-16||Summit Racing||236.97|
|COMP locks, 7 degree, 8mm valve||623-16||Summit Racing||31.97|
|COMP dual valvespring||26925||Summit Racing||184.95|