Valvespring Selection

Valvespring Selection

Picking valvesprings for street and strip is like walking a tightrope
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The pattern is almost always the same: You're in the pits and fire up the engine. It sounds fine. You wing the throttle. It still sounds fine. It's time to idle over to the staging lanes and wait your turn. When the time comes to make the pass, you're confident: The motor pulls aggressively until the tach sweeps past 5,500 rpm. Then all hell breaks loose. The engine begins to pop, bang, and miss. The problem gets worse as you row through the gears. Disgusted, you click it off. The thing won't pull within 2,000 rpm of redline-and it's getting progressively worse. So bad, in fact, that it seems to pick up when you back off the gas. Now what? The ignition system is right on the money and you're absolutely positive that the fuel system is in good shape. Welcome to the curse of the poppet valve engine.

Racers in the know have long been conscious of the effects of valvesprings "going away."

Racers in the know have long been conscious of the effects of valvesprings "going away." And if you breeze through the pits at any drag race, you'll find one thing in common: The vast majority of racers-professional and amateur alike-have the valve covers off their engines. Valvespring inspection and maintenance is critical to performance. Even if one spring is suspect, you can expect a loss in overall performance.

Other than swapping the springs on a regular basis, what can you do to fix the problem? One of the keys is preventative maintenance, but there are a number of other solutions, not the least of which is to buy the right valvesprings in the first place. So we decided to take a look at the world of "little guy" valvesprings: Nothing included here will shock a seasoned pro racer, but some of these inexpensive valvespring fixes might surprise everyone else.

The Spring's Job

A valvespring's job description is pretty cut and dry: It has to store energy so that the valve and its companion hardware can return to the seat. Sounds simple enough, and it is-until engine speeds increase. At higher rpm levels, a spring is taxed. This can eventually lead to valve float.

Most people envision valve float in a pushrod engine as the valve lifter physically parting company with the camshaft lobe. While that might (and often does) happen in severe situations, the first phase of the problem actually involves the valve bouncing off the seat. This bouncing action is virtually uncontrolled, and the end result is extended (and unintended) periods of valve overlap. Since the valves bounce open and closed during the compression stroke, power is diluted by a dramatic margin. This rapid bouncing action (coupled with the invasion into the compression stroke) typically causes the engine to pop, bang and miss.

Selecting Springs

Naturally, installing a stiffer aftermarket spring is a good idea. Considering the valve-float circumstances mentioned above, though, it's obvious that there's more to selecting a set of springs than first meets the eye.

The spring's seat pressure is what keeps the valve from bouncing on the seat.

For starters, seat pressure is a very important factor that's often ignored. Keeping in mind the chain of events that creates float, a high open-spring pressure really has nothing to do with controlling valve bounce. The spring's seat pressure is what keeps the valve from bouncing on the seat. Of course, other factors influence valve bounce at its seat: camshaft lobe profile, valve weight, guide configuration, and more. Maintaining adequate valvespring seat pressure is mandatory, though. Because of this fact, virtually all camshaft manufacturers will readily provide you a minimum spring seat pressure for a given cam profile.

Why can't you just slide in the biggest available springs and be done with it? That'll work with a roller camshaft designed for drag racing only, but for use with a flat tappet camshaft of any sort (hydraulic or solid), too much spring can be worse than too little. Typically, a spring with anything more than 335 pounds of pressure on the nose (open pressure) will rapidly increase the wear on a flat tappet camshaft (along with wear in other areas such as cast-iron guides). Depending on the engine design, the cam profile and the valvetrain geometry, the practical limit for open pressure on a flat tappet cam is approximately 375 pounds. Any more and you'll probably be faced with a pile of broken camshaft pieces.

Simply stated, heavier springs require more horsepower to move the valvetrain.

But there's more to the "too much is just right" scenario. If (and it's a big IF) the engine can physically live with a large amount of open spring pressure, you're still behind the 8 Ball. Why? Large amounts of valvespring pressure can eat horsepower. Increasing the open pressure by 50% also increases the amount of friction inside the engine. Simply stated, heavier springs require more horsepower to move the valvetrain. In the end, oil temperature increases and power levels can drop by five, six or more horsepower.

In effect, selecting valvesprings is much like walking a tightrope. Too little seat pressure creates an open invitation to valve bounce and float. Too much open pressure can physically break the camshaft. In order to arrive at a happy (and workable) medium, the correct spring for the intended RPM range should be selected. But before purchasing springs, you have to determine how much "room" is available in your application. The following example looks at a typical Rat motor with a flat tappet camshaft. Look at the facts and figures and plug your numbers into the mathematical model for your application.

Valvespring Math

Our sample flat tappet camshaft is designed with the following gross valve-lift figures:

Intake: 0.5865"
Exhaust: 0.6300"

Exhaust: 0.6300"

The valvespring specifics (typical for a Chevrolet big-block with a flat tappet camshaft):

Intake: 0.5865"

Solid height: 1.100"

Outside Diameter: 1.487"

Seat Pressure: 116 pound @ installed height

Open Pressure: 310 pound @ 0.560" valve lift

The valvespring specifics (typical for a Chevrolet big-block wiht a flat tappet camshaft):

Without taking the value lash into consideration, the available valvespring "room" works out like this:

(1) Avalilable Spring (Installed Height minus Solid Height): 1.880" - 1.100" = 0.780"

(2) Net Intake (Available Spring minus Maximum Intake Lift): 0.780" - 0.5865" = 0.1935"

(3) Net Exhaust (Available Spring minus Maximum Exhaust Lift): 0.780" - 0.6300" = 0.150"

This combination has a certain "fudge factor" built in: available room for added spring shims, spring seats (required with aluminum heads) and further adjustment. Unfortunately, some combinations aren't blessed with this luxury. According to Crane Cams, "The spring travel of some late-model engines, especially Fords with exhaust rotators, have very short spring travel, sometimes barely enough for the stock cam, much less an aftermarket cam. The only correct way to check spring and retainer travel is to measure the assembled height of the spring when it is assembled on the head. Then (with the piston out of the way), depress the spring and retainer assembly with an on-head spring compressor until the assembly stops moving. Measure the spring height at the point. The difference between the two measurements is the total travel. This travel must be at least 0.060" more than the valve lift of the cam you are using." Sound advice, but in the end, you have to check your numbers carefully before taking drastic measures such as shimming the spring for more pressure or swapping in a different aftermarket spring (especially one that features a longer length or shorter stack/solid height).

Any time the actual spring is stiffened, then the natural resonance is increased. The spring damper counteracts this phenomenon.
Spring Configurations

The spring used in the above example is a dual style, complete with a damper. The spring damper (if so equipped) is designed to absorb spring vibration. To oversimplify, spring vibration is much like a sound resonance traveling through the valvespring. If this resonance is timed just right, then the valvespring actually loses its effectiveness as a spring. Any time the actual spring is stiffened, then the natural resonance is increased. The spring damper counteracts this phenomenon.

Typically, a damper will be constructed with flat sides. The sides of the damper fit tightly against the inner portion of the spring. As the valvespring goes through its motion, the damper actually rubs the side of the outer spring. In turn, it "damps" out the resonance or vibration (to a certain degree).

The inner spring in a dual-spring package can accomplish almost the same job as a damper. Typically, the inner spring will feature much lighter construction than the outer spring. Because of this, it vibrates or resonates at a much different (higher) rate than the outer spring. With different points of resonance or vibration for the inner and outer springs, then the ultimate RPM potential for the spring is increased over a single spring-even if the dual-spring package has identical open and seat pressures when compared to the single spring. Of course, this is seldom the case: In almost all applications, the added inner spring serves to increase both the open pressure and the seat pressure of the overall spring package.

Given a choice (and if your application can accept it), use the dual-spring/damper combination.

A common combination is a dual spring with a damper. Essentially, the use of a damper with a dual spring allows the spring package to deliver more RPM without excessive spring pressure. However, the damper won't account for major gains over and above a common dual-spring setup without a damper. And where the dual valvespring is perfectly matched to the camshaft application, a damper isn't totally necessary. On the other hand, past experience has shown that a dual-spring package complete with a damper provides better spring life over the long haul. Given a choice (and if your application can accept it), use the dual-spring/damper combination.

What about triple springs? For the most part, triples are best used in roller camshaft applications. They work very well in short bursts of extreme RPM, but in many mild applications, a run-of-the-mill double-spring/damper combination will work just as well. Furthermore, the design and construction of an optimized triple-spring package is totally another story in itself.

Stress Relief

Now that we know the basics of valvesprings, what can a racer do to extend spring life? None of these steps will improve spring life if you have the wrong spring for the application, but if you've done your selection homework, they can prolong the spring life-often in a dramatic fashion.

One easy step is to inspect the spring, inner spring and damper carefully before installation. Some valvesprings have added flashing on their ends. (This is also quite common on some dampers). If that's the case with your spring(s), use a small die grinder to carefully smooth the burrs. Similarly, some dampers have very sharp edges on the "flats." The life of the damper can be improved by gently deburring and chamfering this section.

Damper failure is more common than we'd like to think-especially on high-lift, radical-profile camshafts.

We should point out that damper failure is more common that we'd like to think-especially on high-lift, radical-profile camshafts. Occasionally, a damper will physically "unwind," and the lower portion of the assembly will work its way between two lower coils of the outer spring. Naturally, this stacks the spring into coil bind. When that happens, all kinds of carnage can occur if you don't catch the problem immediately. In most cases, selecting the correct length of damper will suffice, but if the problem plagues your application, it can be solved by slightly shortening the damper. Beyond this, and old racer trick is to glass-bead the damper after it's deburred and chamfered.

The end faces of the spring should be dressed prior to installation. Although this sounds exotic, it isn't. Simply polish the ends of the spring smooth on a flat piece of 200-grit wet-and-dry emery paper. Most experts agree that holding the spring upright and using a simple "figure eight" pattern works well for this job. Just be certain that your motion covers all portions of the spring end face. If the surface looks too coarse, repeat the process on 400-grit paper.

The tail end of the spring (where it finally ends) sometimes needs attention. Occasionally, the end will be quite sharp. Not only does this invite stress risers, it can also raise havoc with soft spring retainers (aluminum models) or spring seats. The idea is to gently smooth the sharp edges on the tail. You don't have to re-configure the overall tail shape. Instead, gently break the edges with a whet stone or emery paper.

In the case of a poorly selected spring (or spring retainer), don't be surprised if you see coil bind on the inner spring(s).

Another idea is to pre-stress new valvesprings prior to installation. In other words, the springs are installed in a soft-jaw vise and compressed several times before installation. The idea here isn't to "kill" the spring in a vise and force it into coil bind. Instead, the spring should be compressed gently without physically stacking the spring into coil bind. (Watch the spring carefully as you compress it-instigating coil bind in an 8-inch vise isn't that difficult). Install the spring on the cylinder head and check the seat pressure. If the spring fails miserably, "file" it (or return to the selling dealer) and install a new one. By the way, if you don't have access to a soft-jawed vise, stack some paper notepads on each vise jaw. The thick paper saves the valvesprings from being marred by the steel jaws.

After installing the springs on the cylinder heads, examine the relationship between the inner spring and the damper to both the cylinder head seat and the valvespring retainer. Due to different designs in springs, retainers and spring seats, there might be coil bind at these locations, but no coil bind on the outer spring. Have a close look as the engine is turned through a cycle (by hand). In the case of a poorly selected spring (or spring retainer), don't be surprised if you see coil bind on the inner spring(s). If that's the case, you have to tear everything apart and install an inner spring that suits both the application and the spring retainer.

High-Pressure Lubricant

If you buzz the powerplant on a regular basis and the engine goes into early valve float (or bounce), the spring material can actually become annealed by the heat buildup. The majority of valvesprings are heat-tempered at 400 degrees during construction. Valve float can cause the spring to exceed that temperature by a significant margin. In most cases of valve float, the spring gets so hot that it glows red. This increased heat eventually kills the valvespring.

So what's the solution? Avoiding valve float for one, but what if your combination is always on the edge? In this case, make every effort to maintain adequate lubrication in the cylinder head. Valvesprings can live a much longer life with adequate oil circulation. In a dual-duty application, it's probably best to leave out any oil restrictors. While oil restrictors work well on drag-race-only engines, they can physically starve a street-strip piece.

When it comes to valvesprings, an ounce of prevention is worth more than a few pounds of cure.

On a similar note, take a look at dry-film "coated" valvesprings. A number of friction-reducing coatings are available for valvesprings, but these coatings generally consist of an extreme-pressure lubricant containing molybdenum disulfide that is permanently bonded to the parent part (in this case, the valvespring). In most cases, the coating will be very thin (typically less than 0.0005" in thickness) and will have no appreciable effect on spring fit. Springs that are coated will have measurable amounts of friction reduction, reduced wear as well as a resistance to galling. Many companies apply these coatings, but valvesprings (such as the Crane models shown in the accompanying photos) are available as pre-coated assemblies. Coated valvesprings are slightly more costly than standard models, but if heat reduction in the spring is mandatory, it's a small price to pay.

When it comes to valvesprings, an ounce of prevention is worth more than a few pounds of cure. Springs should be regularly checked using a seat pressure tester. Seat pressure testers simply slip over the rocker arm. Add a bit of muscle power and pull down on the tester. The number that appears on the beam scale (it works like a beam torque wrench) is the spring seat pressure. If the seat pressure is down from the specifications, it's a good sign that the valvesprings are on their last legs. Make it a practice to check the spring seat pressure every time the valves are lashed. This checking procedure will add less than 15 minutes to your normal maintenance schedule.

When all is said and done, the real enemies of valvesprings are heat, excessive RPM (for the application) and incorrect spring selection and installation. Choose the right springs, detail them carefully and include seat pressure checks in your normal maintenance schedule. You might find that walking the valvespring tightrope isn't so difficult after all.

Resources

Competition Cams, 3406 Democrat Rd., Memphis, TN 38118, (901) 795-2400, www.compcams.com

Crane Cams, 530 Fentress Blvd., Daytona Beach, FL 32114, (904) 252-1151, www.cranecams.com

Moroso Performance Products, 80 Carter Dr., Guilford, CT 06437, (203) 453-6571, www.moroso.com

Valvespring Selection
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