Old school thinking on these matters has usually been to increase spring pressure as much as possible by using the stiffest dual or triple springs that can be installed in the engine. But that kind of thinking is changing, thanks to improvements in spring technology.
Stiffer springs are obviously needed if you are building a high rpm performance engine. But the stiffest springs are not necessarily the best anymore. If you can achieve essentially the same degree of valve control with a lower spring rate, the springs will last longer and be less apt to break.
Several spring manufacturers we interviewed for this article told us that there have been significant improvements in the quality of the wire that many source from Japan for making springs. It’s called “super clean wire” because it contains almost no inclusions or imperfections. When the wire is formed, it is rolled in such a way that any inclusions in its microstructure are pushed to the center of the wire.
The center experiences the least stress, so the overall strength and durability of the wire is enhanced. The wire is then scanned with an electrical eddy current to reveal any hidden imperfections. If an imperfection is found, the spot is marked with a dab of paint, and all the wire up to several feet in either direction from that imperfection is discarded when it is made into a valve spring.
Because of these improvements, the wire that’s available to spring manufacturers today for making top-of-the-line high performance valve springs is much better than it was five to ten years ago. The ultimate tensile strength rating of the wire has gone up about 10 percent from where it used to be. This may not sound like much, but in a slightly stressed valve spring it can make a huge difference in performance and durability. Consequently, valve springs can be made smaller and lighter to handle more total valve lift and higher engine speeds without breaking.
Spring manufacturers are also using special surface finishing procedures to extend spring life. Shot peening has long been used to create compressive residual stresses in the outer layer of the spring wire. Shot peening leaves a matte finish on the springs, while hardening the surface to help the spring handle higher loads and speeds without failing.
Nitriding has a similar effect. By diffusing nitrogen into the surface of the spring, the surface is made harder and stronger.
Polishing is another technique that’s used to extend spring life. Small nicks in the surface of a spring can form stress risers that may lead to cracking and failure. By micropolishing the wire to a mirror-like finish, the stress risers are eliminated along with any chance they might cause the spring to fail.
The shape of the wire can also influence its physical properties. Over the years, ovate wire that has an oval cross-section has been used to make some high performance springs. The main advantage with the slightly flattened wire is that a spring of a given installed height can handle more valve lift without the coils binding. So for applications where installed height is limited, a valve spring made of ovate wire may be needed with a high-lift cam.
The drawback with ovate wire is that the spring forming process is more difficult to control. The wire must be carefully oriented within a certain number of degrees with respect to the spring axis; otherwise it can twist and end up in the wrong position. This may create interference problems as well as spring failure issues.
So for this reason, most of the performance valve springs for high-end racing applications use round wire. It’s easier to control during the manufacturing process, and with the new super clean wire can provide increased lift clearance by using smaller diameter, stiffer wire with fewer turns.
Smaller, Lighter, Stronger Springs
One trend that has emerged in recent years is the use of smaller diameter valve springs. Several spring manufacturers now offer cylindrical double springs for small block Chevy, LS Chevy engines and other applications with an outside diameter of 1.32?. The advantages of using a small spring is that the spring has less mass, so it can handle higher rpms with less spring pressure. Or, you can run the same spring pressure as before with a smaller spring and get more rpms out of the engine without losing valvetrain control.
One manufacturer (Comp Cams) has recently introduced a couple of new 1.32? outside diameter springs. One is a polished double spring rated at 400 lbs. per inch that can handle .650? of maximum valve lift. The other is a micropeened double spring rated at 505 lbs. per inch that can handle .654?of lift.
Other manufacturers (PAC Racing and Manley) now have 1.5? O.D. double valve springs for drag racers that can be used in place of triple springs. The double springs are lighter (30 to 50 grams), and can handle up to 1.00? of maximum valve lift. Using the lighter springs provides much the same benefit as using lighter valves. There’s less strain on the valvetrain so the valve springs can control motion and harmonics better.
The amount of valve spring pressure that’s required depends on the application, the type of racing, the weight of the valvetrain components, the design of the valvetrain, and peak engine rpm. Every additional 100 rpm may be worth an extra 20 or more horsepower on a highly modified performance motor.
For small block street performance engines with a flat tappet cam and no more than .450? of lift, single springs with 80 to 90 lbs. of seat pressure is usually all you need. For a street/strip performance engine, single springs with 100 to 120 lbs. of seat should do the job. For street hydraulic roller cams, seat pressure should typically be 105 to 140 lbs., and should not exceed a maximum of 150 lbs. with a mechanical roller cam.
NOTE: Today’s motor oils contain very little ZDDP (zinc) anti-wear additive. This change was necessary to extend the life of the catalytic converter. Roller cams don’t require much ZDDP because there is much less friction on the cam lobes. But with a flat tappet cam, there may not be enough ZDDP to prevent cam lobe wear even with stock valve springs, let alone stiffer performance valve springs. For this reason, some type of ZDDP additive should be used in the crankcase if the engine has a flat tappet cam. Luckily, ZDDP additives are very easy to find these days.
On late model Chevy LS engines, the stock valve springs only have 105 lbs. of seat pressure when closed, and 290 to 300 lbs. open. Many Pro Stock drag motors, by comparison, have double or triple springs with closed seat pressures of 400 to 500 lbs., and open pressures in the 1,350 to 1,450 lb. range. They need this kind of pressure to handle 9,000 to 10,000 rpm engine speeds with relatively large valves and heavy valvetrains. But durability isn’t as important because the runs are short and they typically replace the springs after a few runs.
With NASCAR, the requirements are different. NASCAR engines are also high revving engines, but they can’t stop in the middle of a race to change valve springs. The springs have to go the distance. Because of this, they can’t use as much spring pressure. Ten years ago, the typical NASCAR engine was using springs with 200 lb. seat pressure that could handle .700? lift and 9,000 rpm.
Today, thanks to improvements in spring technology, they are now running smaller, lighter springs that generate only 125 to 130 lbs. of closed seat pressure, but can handle higher .850? valve lifts and engine speeds up to 9,600 rpm.
Lightweight titanium springs can offer many of the same advantages as the new super clean wire steel valve springs, but titanium is too expensive for many racers. So most valve spring manufacturers are concentrating their efforts on improving and expanding their product lines with new, high tech springs.
Computer Simulations
The way in which new springs are engineered has also changed in recent years. Many spring manufacturers now use Finite Element Analysis (FEA) software to evaluate new spring designs on a computer before the real spring is ever made.
By measuring the pitch angle of the wire, the wire diameter and wire spacing, the computer simulation can reveal where the points of greatest stress are so the design can be optimized for maximum strength and durability. The software can accurately predict how many cycles the spring can withstand before it fails under various operating conditions. The software can even simulate spring harmonics, which can be verified by Spintron-testing real springs in a real engine with other valvetrain components.
Some spring manufacturers list the natural frequency ratings of their springs to help engine builders choose springs that will resist harmonic vibrations. There’s no simple correlation between the frequency rating and the rpm ranges where a given spring may experience harmonic vibrations because it can vary depending on the style and weight of the rocker arms, pushrods, lifters and valves.
So it may still require some trial-and-error testing and spring swapping if an engine is experiencing some bad harmonics at a certain rpm range. Hopefully, the spring’s natural frequency will be such that any harmonics that occur will be outside the normal power band of the engine.
One of the advantages of “beehive” springs that are used as original equipment in LS engines and Ford modular V8s is that the narrower coils at the top of the spring create a variable spring rate. This reduces harmonics and allows better performance with a single spring. The smaller O.D. at the top of the spring also allows the use of a smaller and lighter spring retainer.
The disadvantages with the beehive design is that maximum spring pressure is limited because only one spring per valve can be used. So don’t plan on building a 9,500 rpm drag motor with beehive springs. There’s no second spring as a backup to prevent the valve from dropping down into the cylinder head if the spring breaks. The last thing any drag racer wants to do is suck a valve and destroy an expensive CNC-ported aftermarket cylinder head.
Freezing Springs?
Proponents of cryogenics claim all kinds of advantages for deep freezing valve springs and other engine parts. The process involves chilling parts down to about 300 degrees below zero Fahrenheit using liquid nitrogen in a computer-controlled freezer. At such extremely cold temperatures, most molecular vibration stops.
The parts are allowed to cold soak for up to 24 hours or more. This allows the atoms in the metal’s microstructure to settle down and rearrange themselves into a more densely packed state. The change in metallurgy helps relieve residual stress in the parts that can cause cracks and failure, and it helps some parts hold up better by slightly increasing their surface hardness.
These are all positive changes for a valve spring, but the degree to which a cryogenic treatment improves a valve spring will vary depending on the wire in the spring. One manufacturer said for the average valve spring, it may increase spring life several fold. But for really high quality valve springs, they have not seen enough improvement to justify the extra cost. Even so, if a racer wants his valve springs frozen it isn’t going to hurt anything either.
Retainers
Lighter is better when it comes to spring retainers, no doubt about that. But cost is also a factor most racers have to consider. Titanium is lighter than steel, but titanium is expensive and it is not as hard as steel. This may create wear problems even if a special hard surface coating is used. The most common titanium retainers are Ti64 alloy, and a higher grade Ti17 alloy.
Most spring manufacturers now offer some type of lightweight steel valve spring retainer that is nearly as light as titanium, is much stronger and costs a lot less. Alloys used include chrome moly steel and a hard alloy similar to spring steel. The hardness of the steel alloys are typically in the 50 Rc range compared to 30 Rc for titanium, and the difference in weight in many cases is only a couple of grams thanks to FEA computer software that allows the parts to be optimized for maximum strength and lightness.
The lightweight steel retainers go hand-in-hand with the latest generation of lightweight stainless steel rocker arms that many racers are now using. Steel rockers are much stronger than aluminum rockers, and can be made nearly as light with FEA analysis software these days. So for racing applications that require extremely high spring pressures, or extreme durability, shaft-mounted steel rockers are the hot setup.
Installation Issues
Before you can choose a spring and retainer combination for a particular engine, you first need to establish what the installed height of the springs will be. This dimension is essential to determine how much lift the springs can handle before you run into coil bind problems, and how much spring pressure a given spring will exert once it is installed. The installed height is determined by measuring the distance between the spring seat in the head and the underside of the retainer on the valve stem.
With high lift rocker arms, you have to measure the net lift at the valve to make sure the coils don’t run out of clearance and bind.
As a rule, springs should have a safety margin of .060? of remaining travel at maximum valve lift to avoid coil bind.
The minimum clearance between the retainer and valve guide at maximum valve lift should also be .060?.
Less clearance increases the risk that the spring coils will touch or the retainer will bottom out on the top of the valve guide, forming a solid mass that will prevent further valvetrain motion. Something has to give, and that something is usually the pushrod. An engine that is bending pushrods is either running out of clearance, or it needs stronger pushrods.
If high lift springs are not available for a particular engine application, you can gain more clearance by either raising the installed height of the valve or lowering the spring seat. But both of these will also reduce spring tension, which is not the way to go in a high revving engine.
Shims can be used to adjust spring pressure with a given installed height. But the addition of a shim will also reduce the maximum amount of lift a spring can handle before it binds.
Shims are made of hardened steel, come in various thicknesses and are usually serrated on one side to prevent rotation (the serrated side faces the head). Some shims are also designed to help insulate the springs from heat generated by the cylinder head.
Springs should also be lubricated when they are installed in a new engine, especially double and triple springs, to reduce friction. Soaking the springs in oil or coating them with assembly lube should provide adequate protection during the critical first start-up.
When the valve locks are installed around the valve stem, their edges must not touch each other. They should clamp against the valve stem and hold it securely. Keep in mind that the design of the retainer affects the installed valve height and spring tension.
For a complete list of valve spring manufacturers, refer to our High Performance Buyers Guide.
