The Offenhauser engine, familiarly known as the "Offy", was developed by Fred Offenhauser and his employer Harry Arminius Miller.
Impressed by the double overhead cam, four valve per cylinder design, which was a great leap forward at the time, they designed an engine on similar principles. Originally sold as a marine engine, in 1930, a four-cylinder, 151 cubic inch (2.5 L) Miller engine installed in a race car set a new international land speed record of 144.895 mph. Miller developed this engine into a twin overhead cam, four cylinder, four valve per cylinder 220 cubic inch (3.6 L) racing engine.
When Miller went bankrupt in 1933, Offenhauser and another Miller employee, Leo Goossen, bought the shop and the rights to the engine, which they further developed into the Offenhauser engine.
One of the keys to the Offenhauser's success was power. A 251.92 cubic inch (4,128.29 cm³) twin-cam four-cylinder racing Offy with a 15:1 compression ratio and a 4.28125 x 4.375 inch bore and stroke, could produce 420 horsepower (313 kW) at 6,600 rpm; 1.77 horsepower per cubic inch (81 kW/L).
From 1934 through 1960 the Offenhauser engine dominated American open wheel racing, winning the Indianapolis 500 24 times. By then, the company had already been sold, right after World War II, to Meyer-Drake, who continued to build the engines. From 1950 through 1960, Offenhauser-powered cars won the Indy 500 and achieved all three podium positions, winning the pole position in 10 of the 11 years.
When Ford came on to the scene in 1963, the Offy lost its dominion over Indy car racing, although it remained competitive through the mid 1970s even with the advent of turbocharging.
The final 2.65 litre 4 cyl Offy, restricted to 80 in Hg (39.3 psi) turbo pressure, gave 770 bhp at 9,000 rpm. However, the Ford Cosworth DFX soon proved to be unbeatable and the Offy's last victory came at Trenton in 1978, in the hands of Gordon Johncock's Wildcat. The last time an Offy-powered car raced was at Pocono in 1982 for the Domino's Pizza Pocono 500, in an Eagle chassis driven by Jim McElreath, although two Vollstedt chassis with Offenhauser engines failed to qualify for the 1983 Indianapolis 500.