Spring height is the distance between the spring seat and the retainer. There are 3 important heights to consider when buying valve springs:
- Installed Height - The height of the spring when the valve is closed (zero lift).
- Open Height - The height of the spring when the valve is open (max lift).
- Coil Bind Height - The height of the spring when the coils touch each other.
- Follow this link to learn more about Coil Bind.
How is it measured?
Installed height is measured with a Height Micrometer. This is a tool that installs in place of the valve spring. It expands to seat the valve. Then, the reading on the micrometer is the required installed height.
Open height is a calculated value. It is found by subtracting the max Valve Lift from the installed height.
Open Height = Installed Height - Max Valve Lift
Coil bind height can be found by fully compressing the spring in a vise. Then, measure the spring with a Caliper.
How does it affect performance?
Valve spring height is important because it, along with the Spring Rate, sets the Spring Pressure.
- Installed height sets the seat pressure.
- Open height sets the open pressure.
Correct spring pressures keep the engine out of Valve Float.
Knowing the coil bind height is important so that it can be avoided. Coil Bind will damage the engine.
When needed, spring height and pressure can be fine-tuned using Valve Spring Shims.