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H Engine




For the Saab "H" engine (a Straight-4 ) see Saab H Engine


An H engine (or H-block) is an Engine Configuration in which the Cylinder s are aligned so that if viewed from the front appear to be in a horizontal letter H .

An H engine can be viewed as two Flat Engine s, one atop the other. The "two engines" each have their own Crankshaft , which are then geared together at one end for power-take-off. This leads to a worse Power-to-weight Ratio than simpler configurations with only one shaft. The only obvious advantage of the H configuration is to allow the building of reasonably short engines with more than 12 cylinders, their compact size being useful as Aircraft Engine s where their small size allows for better Aerodynamics - see Lycoming .

The H configuration is therefore very uncommon. Known examples are:

  • The British Racing Motors H-16 Formula One engine, which was a major failure. This engine was powerful but heavy and unreliable, had low torque and a high Center Of Gravity . Jackie Stewart is believed to have said "This piece of metal is better used as a ship's anchor than as a power plant". Despite its poor reputation Jim Clark managed to win the 1966 US Grand Prix with a Lotus 43 powered by this engine.

  • The Lycoming H 2470 Hyper Engine , that did not go into production.

  • The Napier Rapier , Dagger and Sabre airplane engines. Unlike the BRM and the Lycoming, the Sabre eventually matured into a superb design.


Subaru produces water-cooled Flat-4 and Flat-6 "Horizontal" engines that are marketed as H-4 and H-6, despite the fact that their configuration has nothing to do with a real H engine.