BRM H16 engine

The BRM H16 Formula One engine in its final, 64-valve incarnation.

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.[1]

Two straight engines can be similarly joined to provide a U engine.

H enginesEdit

Aircraft enginesEdit

Napier Sabre

Napier Sabre H-24 engine. The two starboard 6-cylinder banks can be seen in this view

Other enginesEdit

Brough Superior Golden Dream (close up)

Brough Superior H-4 motorcycle engine

BRM H16 in P83

A BRM H16 engine, mounted in the back of a BRM P83 Formula One car.

Other uses of H termEdit

Subaru produces water-cooled flat-four and flat-six "Horizontal" engines that are marketed as H4 and H6 (also thought to represent the configuration of the cylinders from a 'top down' POV as opposed to the traditional 'head-on' POV).


  1. Willoughby, Vic (1989). Classic motor cycles. Ivy Leaf. ISBN 0863630057. 
  2. "BRM engines H16". Retrieved on 2010-09-12.
  3. Wilson, Hugo (1995). "Brough Superior Dream", The Encyclopedia of the Motorcycle. London: Dorling Kindersley, 34–35. ISBN 0 7513 0206 6. 

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