With the new Observer blocks it is possible to create an incredibly fast and compact engine that can be single-directional or bidirectional.

The image above shows you how to build it layer-by-layer. For a bidirectional engine make both pistons sticky, for signge-directional engine make only the piston at the side you want to move to sticky. It is that simple. (e.g. if you want the engine to be single-directional and move to the left, make the left piston sticky and the right piston not sticky)

To start moving in the opposite direction after stopping, simply power the piston that is facing the direction you want to move to, with a 1-tick pulse.

The second image demonstrates how fast this new engine is compared to the previous best engines. (the obsidian on the left is the starting line)

Very easy to build, very simple to use, the most compact and the fastest engine possible!