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An H engine (or H-block) is an engine configuration in which the cylinders are aligned so that if viewed from the front, they appear to be in a vertical or horizontal letter H.
An H engine can be viewed as two flat engines, one atop or beside the other. The "two engines" each have their own crankshaft, which are then geared together at one end for power-take-off. The H configuration allows the building of multi-cylinder engines that are shorter than the alternatives, sometimes delivering advantages on aircraft. For race-car applications there is the disadvantage of a higher center of gravity, not only because one crankshaft is located atop the other, but also because the engine must be high enough off the ground to allow clearance underneath for a row of exhaust pipes. The power-to-weight ratio is not as good as simpler configurations employing one crankshaft. There is excellent mechanical balance, especially desirable and otherwise difficult to achieve in a four-cylinder engine.
Two straight engines can be similarly joined to provide a U engine.
- Fairey Aviation
- Klöckner-Humboldt-Deutz DZ 720 - H-32, 102.9 litres
- Napier & Son, UK.
- Napier Rapier (1929) - H-16 air-cooled vertical, 8.83 litres 340 hp
- Napier Dagger (1934) - H-24, air-cooled vertical, 16.85 litres 890 hp, a development of the Rapier
- Napier Sabre (1938) - H-24, water-cooled horizontal sleeve valves, 36.7 litres 3,500 hp.
- Pratt & Whitney
- Rolls-Royce Eagle (1944) - H-24, 46.2 litres, 3,200 hp.
Brough Superior H-4 motorcycle engine
Other uses of H term
Subaru produces water-cooled flat-four and flat-six "Horizontally-opposed" engines that are marketed as H4 and H6 which are not to be confused with H-block engines. The naming scheme refers to engine description, simlar to inline engines being named I4 or I6, rather than their appearance front-on.
- ^ Willoughby, Vic (1989), Classic motor cycles, Ivy Leaf, ISBN 0-86363-005-7.
- ^ "BRM engines H16". Members.madasafish.com. Retrieved 2010-09-12.
- ^ Wilson, Hugo (1995). "Brough Superior Dream". The Encyclopedia of the Motorcycle. London: Dorling Kindersley. pp. 34–35. ISBN 0-7513-0206-6.
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