Vapor lock index
Also known as: VLI
VLI = 10x(Vapor pressure in kPa) +7x(% evaporated at 70C)
Typical values range from 800 to 1,250, and lower VLI is better.
In the US, vapor lock is controlled by the vapor-liquid ratio rather than VLI. Vapor-liquid ratio is the temperature at which gasoline forms a ratio of vapor volume to liquid volume that is equal to 20.
The normal range for vapor-liquid ratio is 35 to 60 C (95 to 140 F). Higher vapor-liquid ratio is better.