what valve springs should i use

Internal Combustion Engine Valve Spring Characteristics

Valve springs are critical components in internal combustion engines responsible for closing the valves after they have been opened by the camshaft. Their proper function ensures efficient engine operation and prevents valve float.

Functional Requirements

  • Valve Closure: Providing adequate force to consistently and rapidly seat the valves against the valve seat, maintaining cylinder sealing.
  • Cam Follower Control: Maintaining contact between the cam follower and the camshaft lobe profile throughout the engine's operational speed range.
  • Prevention of Valve Float: Avoiding a condition where the valve loses contact with either the cam follower or the valve seat due to insufficient spring force.

Key Spring Parameters

  • Spring Rate: Measured in pounds per inch (lbs/in) or Newtons per millimeter (N/mm), indicating the force required to compress the spring by a given distance.
  • Installed Height: The height of the spring when installed on the cylinder head, with the valve closed. This is a crucial dimension.
  • Open Height: The height of the spring when the valve is fully open. This is determined by valve lift and installed height.
  • Coil Bind Height: The minimum compressed height of the spring where the coils are fully compressed and touching each other. Operation beyond this point can cause damage.
  • Seat Pressure (Installed Load): The force exerted by the spring at the installed height.
  • Open Pressure (Open Load): The force exerted by the spring at the open height.
  • Wire Diameter: The diameter of the spring wire, affecting spring rate and durability.
  • Number of Coils: The number of active coils in the spring, also impacting spring rate.

Types of Springs

  • Single Springs: A simple, cost-effective design.
  • Dual Springs: Two springs, one inside the other, offering increased spring rate, damping, and resistance to fatigue. Often, the inner spring serves as a damper.
  • Triple Springs: Less common, offering the highest spring rates and durability for extreme applications.
  • Beehive Springs: Tapered springs with a smaller retainer, reducing valvetrain mass and improving high-RPM performance.
  • Progressive Rate Springs: Springs designed with varying coil spacing to provide different spring rates at different compression levels.

Material Considerations

  • High-Tensile Steel: The most common material.
  • Chrome Silicon Steel: Offers increased strength and heat resistance.
  • Titanium: Provides exceptional strength-to-weight ratio but is more expensive. Often used in retainers.

Factors Influencing Selection

  • Camshaft Profile: More aggressive camshafts with higher lift and faster ramp rates require stronger springs.
  • Engine RPM: Higher engine speeds necessitate springs with higher rates to prevent valve float.
  • Valve Train Weight: Lighter valves and retainers reduce the required spring force.
  • Valve Lift: Greater valve lift requires springs that can accommodate the increased compression.
  • Operating Conditions: Engines operating under high heat or stress conditions may require springs made from more durable materials.

Potential Issues

  • Valve Float: Loss of control due to insufficient spring force.
  • Spring Surge: Harmonic vibrations within the spring, leading to premature failure.
  • Coil Bind: Compression beyond the spring's design limits, causing damage.
  • Fatigue Failure: Progressive weakening and eventual breakage due to repeated stress.