Ultimate piston engine, developed from M-251TK. It was designed for long range heavy bombers, 24 cylinders were arranged in 4 raws. Engine diameter - 1.4m, length (with TK-36 supercharger and gearbox) - 2.5m. Powerplant was a success, but rapid progress of turbojets and turboprops chased those monsters from the scene.
Team of OKB-36 was awarded Stalin's Price in 1951 for this engine.
Designation on development stage - M-253K.