Free tools
Valve saturation
Beyond a certain lift, more lift gives no extra flow, because the port becomes the bottleneck instead of the valve gap. Enter the valve head diameter, the port's minimum cross-sectional area and the number of intake valves, and you get the saturation point.
All tools
Saturation point for lift
10,19 mm
The lift where the curtain area meets the port's minimum cross-sectional area. Beyond that point the port, not the valve gap, is the limit. With two intake valves the minimum cross-sectional area must apply to the whole port that feeds both.
How the calculation works
The curtain area is the cylindrical surface that opens between the valve head and the seat at a given lift, that is π times the valve diameter times the lift. The factor 0,98 removes a couple of percent to reflect the effective circumference. Setting the curtain area equal to the port's minimum cross-sectional area and solving for the lift gives the height where the gap just catches up with the port.
Measured in square millimetres divided by a diameter in millimetres, the result comes out directly in millimetres. Beyond the saturation point the port's minimum cross section governs the flow, not the valve lift. With two intake valves the minimum cross-sectional area must apply to the whole port that feeds both valves, otherwise the result is wrong.
Example
A 51 mm valve with a minimum cross-sectional area of 1600 mm² and one intake valve gives a saturation point of about 10,2 mm (roughly 0,40 inch).
What the saturation point means
| Lift compared with saturation | Meaning |
|---|---|
| Below the saturation point | The valve gap limits the flow |
| At the saturation point | Curtain area and minimum cross-sectional area are equal |
| Above the saturation point | The port limits, more lift gives a little extra |
The factor 0,98 is an effective share of the geometric curtain circumference. Real flow is measured on a flow bench.
More tools
Related services
Building for real? We take care of the job.
Common questions about valve saturation
Need help with your engine build?
Describe your project and we will get back to you within 24 hours. Quote after inspection.