Daimler-Benz DB 604
The Daimler-Benz DB 604 was an experimental German 24-cylinder aircraft engine, which did not progress beyond the initial engine testing phase and was ultimately abandoned in September 1942.
The DB 604 was unique among the DB 600 series of aircraft engines by having its 24 cylinders arranged in an X, with four inline rows of six cylinders. The DB 604 was also unique amongst the X-24 engines, in that it was not conceived as a further development of existing Daimler-Benz aircraft engines such as the DB 601, DB 603 or DB 605, which themselves had been twinned-up as two separate powerplants sharing a new common gear reduction case at their front ends, into the "coupled" DB 606, DB 613 and DB 610 "power systems" respectively, starting before World War II.
The DB 604 was a completely new Daimler-Benz engine design featuring a perfectly square stroke ratio of 135 mm x 135 mm. The square stroke ratio enabled the relatively high engine speed of 3,200 rpm. The first engine tested in 1939 on the engine test stand achieved a power output of 1,725 kW (2,350 hp).