Darracq was an important early French aircraft engine manufacturer. A contemporary reference is the 1920 book by E. Charles Vivian (ECV) in which a chapter covers horizontally-opposed aircraft engines. The Darracq engines are described as notable engines among several HOAE from various countries. Vivian's book is available on the Internet and can be found here. Another reference is Setright's book (LJKS).
OL-195 -- {5.118 / 4.724 / 194.4} / {130 / 120 / 3186}
Same bore and stroke as OL-390.
2cyl; N/A; 25-30hp@1500rpm; 1907-1914; Wt = 121#.
Liquid-cooled, single-ignition engine.
Ae39; J1912; LEO.
Applications: (France) deBrageas monoplane (8 built for Russia); Nieuport IIB; Santos-Dumont XX Demoiselle (Bébé, JouJou).
OL-390 -- {5.118 / 4.724 / 388.8} / {130 / 120 / 6371}
Same bore and stroke as OL-195.
4cyl; N/A; 50-60hp@1500rpm; 1909-1914; Wt = 242#.
Liquid-cooled engine.
Ae39; J1912; LEO.
Applications: (France) Bonnet-Labranche No. 5.