Be The Camshaft Expert

Retainers & Keepers
Retainers and keepers (also known as locks) have a simple job, but they sure take a beating doing it. When selecting retainers, bear in mind they must fit snugly on the springs with which they are to be used. Also, they need to be as light as possible, consistent with surviving. Valves are made with various groove styles, the most common being the square lock and radius lock. The grooves in the valves and the step in the keepers are not there to act as retention for the valve and spring assembly. It is the taper in the retainer driving the keeper to a super-clamping force on the valve stem that, for the most part, holds everything in place.

Retainers and keepers come in two different angles, these being 7 and 10 degrees. Seven-degree retainer/keeper combinations are the norm and are used almost universally by the OEM. These work just fine until spring forces escalate to the levels required to run big valve lifts and very high rpm. Under such circumstances the keepers literally bind themselves into the retainers making a teardown really difficult. By going to a 10-degree angle, the clamping force of the keeper on the valve stem is reduced, but teardown is far easier.

Springs
The most important aspect of a high-speed valvetrain is the spring. It is entirely true to say that the valvetrain is, at best, only as good as the spring. What we want from a spring is near infinite fatigue life, low mass and a high delivered force. Striving for these mechanical virtues produces a long-life spring with a high, natural vibration frequency, or to give it its technical term, resonant frequency. The higher the resonant frequency, the less likely the spring is to go into surge. Without steps to abate it, surge can occur at a number of points as rpm increases. Basically, surge causes the valvetrain to lose some or all control of the valve motion. The result is loss of output at whatever rpm it occurs.

Interference fits between two oppositely wound springs, as in a typical dual spring or a dual spring and flat wound damper, are methods used to damp spring surge. When selecting a spring, consider the delivered force versus the weight of the spring. An 80-gram spring that delivers 110 lbs on the seat and 300 over the nose will control the valvetrain far better than one with the same poundage but weighing in at 110 grams.

Dual and damped high-performance springs have been the valvetrain designer's number-one means of getting the job done for better than half a century. By about 20 years ago, most of the development potential of the dual (or triple) parallel-wound springs had been used. Steel alloys were not going to get much better without some big breakthrough, and titanium, being stiff and light, was a viable alternative, but was expensive and difficult to work.

With gains from conventional materials at a near standstill, the other option spring specialists had was to look at spring design to see if there was a better alternative to the parallel-wound conventional spring. Turns out there was, and during the mid 1980s GM began research on the application of a design known as the "beehive" spring. As its name suggests, this spring is wound in a beehive form. With each coil getting progressively smaller, this spring has no clear-cut resonant frequency. As soon as it starts to resonate at a particular frequency, the resonant frequency changes. Result: Spring surge is, in almost all applications, reduced to levels bordering on insignificant.

The beauty of the beehive spring is that it uses its delivered force far more effectively than a conventional parallel-wound spring. It needs far less of its delivered force to control its own motion, so this leaves more to control the valvetrain. This means less overall valve-spring loads while delivering more rpm. Our spin tests on a street roller cam showed an rpm increase from 5,950 to 6,900. This was achieved with a beehive spring (COMP Cams PN 26918) with 8 lbs less on the seat and 20 less over the nose than its parallel-wound counterpart. Because of the propensity of hydraulic roller lifters to collapse easier than their flat counterparts, beehive springs are well-suited to hydraulic rollers. Reduced loads and better control pay off in terms of added output and rpm. The two occasions tests were run, both in small-block Fords (302 and 392), showed about a 6hp gain in each, but considering just the change in peak hp is only a small part of the story. Take a look at the graph showing the before and after tests of the beehive spring, p. 78. What you see here is a valvetrain that retains control to significantly higher rpm. The regular spring, in spite of being stronger, hit valvetrain crash at a shade over 6,000 rpm, but it was progressively losing control (or collapsing the lifter or a combination of both) at 5,700 rpm. The beehive spring kept it all together up to about 6,600, although power figures were only recorded to 6,400. At 6,000 rpm the beehive's ability to deliver superior control netted an increase of some 65 hp.

Valves and Mass
For the type of valvetrains we are looking at, the mass of the valve is as significant as that of the spring/retainer combination. From the tech point of view there are no dark issues to comprehend. The golden rule is the lighter the better. With lighter valves the amount of acceleration imparted to the valve can be increased either by a more aggressive cam profile or a higher lift rocker. The faster the intake can be opened and closed the greater the engine's output potential. For the exhaust, things are somewhat different in as much as a fast-opening exhaust valve action is not required. Indeed, it is possible to open the exhaust valve too fast and actually reduce output. Costwise, this can actually play into our hands.

Most of us use stainless valves because they are relatively inexpensive. Top-of-the-line lightweight valves are made of titanium, and they cost something bordering an arm and a leg. Fortunately, Ferrea makes a stainless valve that is better than a halfway house at less than a halfway house price. These are their hollow-stem valves. The nearby Spintron tests show where each type of valve lies in the grand scheme of things.

Cost is an ever-present barrier, but there are ways to maximize a valvetrain's ability to run the best rpm possible per valve dollar spent. By juggling valve types between intake and exhaust, we can make the most of our valve budget dollars. Remember, only the intake has to be opened fast. Because the exhaust valve is smaller and consequently lighter and is usually run with a lower-lift rocker, we find that we can use a hollow-stem intake and a less expensive solid-stem exhaust. The same move can be applied if you can go upscale on cost. A combination of a titanium intake with a hollow-stem stainless exhaust works just about as well as having both valves of titanium. Not only is this less costly, but for a long distance engine it is actually more durable.

Next Month...
If you absorbed all this, you should be well along the road to being a cam guru. What we have not touched on, however, is physically timing-in cams and the consequences of advancing and retarding the cam. This will also be a vital part of your cam and valvetrain education, but it warrants a feature all its own. Check PHR next month for the rest of the story.