The Offenhauser:
One of the keys to the Offenhauser engine's success and popularity was its power. A 251.92 cubic inch (4,128.29 cm³) DOHC naturally-aspirated four-cylinder racing Offy with a 15:1 compression ratio and a 4.28125-by-4.375-inch (108.744 mm × 111.125 mm) bore and stroke could produce 420 hp (310 kW) at 6,600 rpm (1.77 hp per cubic inch, 81 kW/L) making it remarkably power-dense. Other variants of the engine produced even higher outputs of 3 hp per cubic inch (137 kW/L), unparalleled for their size and capacity in power-to cubic-inch/cylinder-count ratio. Another reason for the engine's success was its reliability. Its monobloc construction made it immune to head gasket or cylinder stud problems, and allowed for higher cylinder pressures.
From 1934 through the 1970s, the Offenhauser engine dominated American open-wheel racing, winning the Indianapolis 500 27 times. From 1950 through 1960, Offenhauser-powered cars won the Indianapolis 500 and achieved all three podium positions, winning the pole position in 10 of the 11 years.
Offenhauser produced engine blocks in several sizes. These blocks could be bored out or sleeved to vary the cylinder bore, and could be used with crankshafts of various strokes, resulting in a wide variety of engine displacements. Offenhauser (and Meyer-Drake, in later years) frequently made blocks, pistons, rods, and crankshafts to specific customer requests. However, certain engine sizes were common, and could be considered the "standard" Offenhauser engines:
97 cu in (1.59 L) - to meet the displacement rule in many midget series
220 cu in (3.6 L) - displacement rule in AAA (later USAC) sprint cars
270 cu in (4.4 L) - displacement rule for the Indianapolis 500 under AAA rules
255 cu in (4.18 L) - for Indianapolis (during the 1930s fuel consumption rules)
252 cu in (4.13 L) - displacement rule for Indianapolis under USAC rules
168 cu in (2.75 L) - displacement rule for turbocharged engines at Indianapolis (to 1968)
159 cu in (2.61 L) - displacement rule for turbocharged engines at Indianapolis (1969 and later)