Calculating valve spring requirements for engines is a critical aspect of engine building, particularly in high-performance and racing applications where precise valvetrain control is essential for maximizing power and reliability. Valve springs play a crucial role in ensuring the proper opening and closing of the intake and exhaust valves, as well as maintaining valve train stability at high engine speeds.
It has been said that the valvetrain has a pair of dance partners: The camshaft takes the lead, while the valvespring follows while managing the handicap of dancing backwards. This makes choosing valvesprings challenging – which spring will complement your engine best? Here’s a closer look at the process of calculating valve spring requirements for engines.
- Understand Engine Dynamics: Before delving into valve spring calculations, it’s important to understand the dynamics of the engine and its valvetrain. Factors such as engine displacement, cylinder head design, camshaft specifications, desired RPM range, and intended use (e.g., offshore marine, street driving, drag racing, circle track racing) all influence valve spring selection.
- Determine Maximum Valve Lift: The first step in calculating valve spring requirements is to determine the maximum lift of the camshaft. This information is typically provided by the camshaft manufacturer and is specified as the maximum lift at the valve, measured in inches or millimeters.
- Consider Valve Train Weight: The weight of the valvetrain components, including valves, springs, retainers, and lifters, affects the forces exerted on the valve springs. Heavier valvetrain components require stiffer valve springs to control valve motion effectively.
- Calculate Spring Rate: Valve spring rate, measured in pounds per inch (lb/in) or newtons per millimeter (N/mm), refers to the amount of force required to compress the spring by a certain distance. The spring rate determines how much pressure the spring exerts on the valve at different lift points.
- Account for Dynamic Forces: In high-performance engines, especially those equipped with forced induction or high-lift camshafts, additional dynamic forces come into play. These forces include valve acceleration, boost pressure (in supercharged or turbocharged engines), and valve float (the condition where the valve does not fully follow the cam profile). It’s essential to consider these dynamic forces when calculating valve spring requirements to prevent valve float and ensure valve train stability at high RPM.
- Select Appropriate Valve Springs: Based on the calculated spring rate and dynamic forces, choose valve springs that can provide sufficient pressure to control valve motion throughout the engine’s operating range. Consider factors such as material composition, coil bind height, maximum valve lift capability, frequency and compatibility with other valvetrain components.
- Consult with Experts: For complex engine builds or applications where precise valvetrain control is critical, consulting with experienced valvetrain specialists can provide valuable insights and ensure optimal valve spring selection.
If you’re interested in trying out a valvespring estimation tool, Allmond Marine has developed that for you. Contained in it are all the inputs that should be considered when selecting a valvespring.
By accurately calculating valve spring requirements and selecting appropriate springs for the engine’s specific needs, engine builders can achieve reliable valvetrain operation, minimize the risk of valve float or component failure, and unleash the engine’s full performance potential.
