The 1916 Curtiss OX-2 aero engine was a water-cooled eight-cylinder V which produced 100hp from 567.44ci and a dry weight of 401 lb.

Except for a bigger bore, it was almost identical to the OX.

The 1917 Curtiss AB conceptual 12-cyl experimental low-drag, low-weight power engine for fighter planes project was shelved with only one built. The acquired technology went into development of the Curtiss-Kirkham K-12.

Designed by Charles B. Kirkham and first tested in 1916, the V12 K-12 featured a cast aluminum upper crankcase and integral cylinder blocks, four valves per cylinder, and “wet sleeve” construction for improved cooling. It relied upon high rpm and reduction gearing to develop the same power as larger engines. Although technologically advanced, many of the K-12’s innovations challenged the state-of-the-art and created serious reliability problems. Most problems were centered on producing reliable reduction gears. The K-12 design, however, led to the development of the very successful Curtiss D-12 (1922) engine used in fighters and racing planes. By 1926 the D-12 design had evolved into the more powerful Curtiss V-1570 “Conqueror,” noted for its use in military aircraft. That evolution was continued in the powerful liquid-cooled, V-12 aircraft engines of World War II that owed so much to design concepts pioneered in the K-12 engine of 1916.

Curtiss K-12
Type: 12-cylinder liquid-cooled V
Bore: 4.5 in (114.3 mm)
Stroke: 6.0 in (152.4 mm)
Displacement: 1,145.1 cu in (18.77 L)
Cooling system: liquid
Power output: 375 hp / 280 kW at 2,250 RPM
Weight: 307.5 kg (678 lb)
Length 152.4 cm (60 in.)
Width 70.8 cm (27.875 in.)
Height 101.9 cm (40.125 in.)