Why Manton Valve Springs?
A valve spring cannot be accurately judged by seat pressure and open pressure alone. Its shape, wire profile, spring rate, mass, natural frequency, stress level, and operating environment all influence how effectively it controls the valvetrain.
Manton valve springs are designed and selected around the requirements of the complete valvetrain. Our goal is not simply to provide the highest possible spring pressure. It is to supply the force needed to maintain control throughout the engine’s operating range without creating unnecessary load, heat, friction, or wear.
Designed for the Complete Application
Valve-spring requirements can vary substantially from one engine to another. A street engine expected to run for hundreds of thousands of miles has different requirements than a drag-racing, circle-track, marine, or high-boost pulling engine.
Selecting the correct spring requires considering factors such as:
- Common camshaft profiles and valve accelerations
- Maximum valve lift
- Intended RPM range
- Valvetrain mass
- Installed height
- Available coil-bind clearance
- Boost pressure and exhaust backpressure allowances
- External spring cooling availability
- Intended use and maintenance interval
Manton evaluates these factors together to help match the spring’s pressure, rate, travel, geometry, and expected service life to the application.
More Than Seat and Open Pressure
Seat pressure is the force applied by the spring when the valve is closed. It helps keep the valve seated while resisting forces created by spring surge, boost pressure, exhaust backpressure, and combustion pressure.
Open pressure is the force applied when the valve is at maximum lift. It provides the force needed to decelerate the valvetrain as it approaches full lift and accelerate it as the valve begins closing. Proper open pressure helps the lifter remain in contact with the camshaft so the valve can follow the intended cam profile.
However, a valve spring does not operate at only these two positions. The force required to control the valvetrain changes throughout the entire lift cycle.
Manton looks beyond the two pressures printed in a catalog. Spring rate and the available force throughout the lift curve must also be considered. The point where the available spring force comes closest to the force required to control the valvetrain represents the system’s smallest force margin, which Manton refers to as the “minimum gap.”
Maintaining an adequate minimum gap helps the valvetrain remain stable when RPM, heat, component deflection, manufacturing variation, and spring surge reduce the available control margin.
Spring Geometry Selected for a Purpose
No single valve-spring shape is ideal for every application. Manton uses straight, beehive, and conical designs where their individual characteristics provide a meaningful benefit.
Straight Valve Springs
Straight springs maintain a relatively consistent coil diameter throughout their height. They are economical to manufacture, fit well in smaller spring pockets, and make it easier to nest two or three springs together.
These characteristics make straight springs an effective solution for many conventional dual- and triple-spring assemblies.
Beehive Valve Springs
A beehive spring reduces in diameter near the top. Because the upper portion of the spring and the retainer experience the greatest movement, reducing mass in this area can improve valvetrain control.
The smaller upper diameter also allows the use of a smaller retainer, which can be both lighter and stronger.
Conical Valve Springs
A conical spring gradually decreases in diameter from the bottom to the top. This reduces the mass of the upper and intermediate coils, providing a greater reduction in dynamic mass than a spring that tapers only near the top.
The changing coil diameter can also produce a broader range of natural frequencies instead of one dominant frequency. Selected coils may progressively become inactive as the spring compresses, creating additional damping and increasing the spring rate.
As the upper coils stack within the coils below them, the spring can also gain lateral stability. This helps reduce damaging side-to-side movement when the spring encounters severe surge or valvetrain instability.
The vast advantages of a conical valve spring is what encouraged us at Manton to repolarize the conical spring design, featuring this shape whenever it is advantageous.
Wire Geometry That Supports Load and Travel
Round wire is a practical and cost-effective choice for many valve-spring applications. When additional stiffness or travel is required within a limited space, properly designed ovate wire can offer an important advantage.
Stress is not distributed evenly throughout valve-spring wire. The highest corrected torsional stress generally occurs near the inside diameter of the coil. Ovate wire can place additional material in this highly stressed area while removing material where it contributes less to spring strength.
This more favorable stress distribution can allow the spring to carry the required load while providing increased lift capacity and improved fatigue life within the available package.
Controlling Spring Surge and Resonance
Each time a valve opens and closes, stress waves travel through the spring. These waves can temporarily increase or decrease the force produced by the spring. If they are not adequately controlled, the spring can develop surge, lateral motion, and resonance.
This instability can contribute to valve float and increase wear on the valve, valve guide, retainer, rocker arm, pushrod, lifter, and camshaft.
Depending on the application, Manton valve-spring designs can use several methods to control this behavior:
- Different natural frequencies within dual- or triple-spring assemblies
- Controlled friction between nested springs
- Dedicated spring dampers
- Progressive coil contact
- Beehive or conical spring geometry
- Reduced dynamic mass
In a multiple-spring assembly, the individual springs generally have different natural frequencies. If one spring begins to surge at a particular engine speed, the other springs may continue helping control the valve. Controlled interference between the springs can also convert unwanted vibrational energy into heat through frictional damping.
Premium Spring Wire
Few engine components accumulate as many severe load cycles as a valve spring. A spring may deform and return to its original shape thousands of times per minute, accumulating millions of fatigue cycles during its service life.
Because fatigue cracks commonly begin at or near the wire surface, material cleanliness and surface quality are critical. Even a small inclusion, seam, or surface defect can concentrate stress and provide a location for a fatigue crack to begin.
Manton uses premium-quality spring wire selected for demanding valvetrain applications. The material is processed to minimize harmful inclusions near the highly stressed wire surface and inspected so detectable abnormalities can be removed before the springs are manufactured.
Fatigue-Resistant Surface Processing
The surface of a valve spring is especially important because microscopic surface imperfections can grow incrementally during repeated loading until the remaining material can no longer support the applied force.
Properly controlled shot peening improves fatigue resistance by introducing beneficial residual compressive stress into the spring’s surface. This compressive stress helps counteract the tensile stress responsible for initiating and growing fatigue cracks.
Shot-peening intensity and coverage must be carefully controlled. An inadequate process may not produce the desired benefit, while an overly aggressive or poorly controlled process can damage the spring surface.
Because of shortening advantages with near no disadvantages, all of Manton’s valve springs are precision shot peened.
Performance Balanced With Durability
Every spring material has a stress limit. As operating stress approaches that limit, the number of cycles the spring can survive generally decreases. This creates an unavoidable relationship between maximum performance and service life.
A spring intended for a short-duration racing engine may operate successfully at a stress level that would provide unacceptable durability in a street engine. Conversely, designing every racing spring around conservative street-life requirements can sacrifice RPM capability, lift capacity, or packaging efficiency.
Manton matches the spring to the engine’s actual duty cycle. This allows the spring selection to reflect the required performance, expected operating conditions, and realistic maintenance interval.
A Complete Valvetrain Perspective
Available valve lift is not determined by the spring alone. The spring and retainer may encounter other interference before reaching coil bind, including:
- Retainer-to-valve-seal contact
- Retainer-to-rocker-arm contact
- Spring-to-locator or valve-guide-boss interference
- Rocker-arm travel limitations
- Excessive roller sweep across the valve tip
Temperature and lubrication must also be considered. Valve springs generate heat as coils, dampers, and nested springs interact. Oil is often responsible for carrying away much of this heat, but cylinder-head geometry and vehicle acceleration can prevent every spring from receiving the same amount of oil.
Manton’s experience throughout the valvetrain helps engine builders evaluate these interactions and choose components that work together as a system.
Choose the Spring Your Valvetrain Needs
The best valve spring is not automatically the spring with the highest pressure or greatest advertised lift. It is the spring that provides the necessary force throughout the lift cycle, controls surge and resonance, fits the available space, manages stress and temperature, and delivers an appropriate service life.
Manton valve springs combine application-specific selection, purposeful geometry, premium wire, controlled manufacturing processes, and a complete-valvetrain approach to provide dependable control in demanding applications.
Contact Manton to discuss your engine combination or review our valve-spring specifications to find the correct spring for your valvetrain.