VIT has been a traditional feature of Wärtsilä (Sulzer) slow-speed engines allowing to adapt an optimum injection timing over an engine load to various fuel properties having a poor combustion behaviour. Primarily mechanical arrangement, used to keep cylinder pressure high for the upper load range, was changed in the common-rail Wärtsilä RT-flex engines to fully electronically-controlled feature giving longer lifetatime and improved part-load fuel consumption.