A: Yes. It is an unofficial fan modification. As long as you own the base game (OMSI 2), downloading and installing mods is permitted by the developer, Aerosoft.

Do you already have the of your engine?

: Supports 1 to 8 cylinders in configurations including Inline, Vee, Boxer, and Opposed Piston. Free Access vs. Paid Versions

As the piston moves up, it creates a vacuum in the crankcase, pulling in air and fuel. EngMod2T models reed valves, rotary valves, or piston-ported intakes to optimize this volume.