Engine configuration

Engine configuration is an engineering term for the layout of the major components of an internal combustion engine. These components include cylinders, pistons, crankshaft or crankshafts and camshaft or camshafts.

For many automobile engines, the term block is interchangeable with engine in this context, for example V block and V engine can often be used interchangeably in American English. This is because the most common forms are all based on a combined engine block and crankcase that are milled from a single piece of cast metal. The locations of the major components are largely determined by the shape of this one component.

The standard names for some configurations are historic, arbitrary, or both, with some overlap. For example, the cylinder banks of a 180° V engine do not in any way form a V, but it is regarded as a V engine because of its crankshaft and big end configuration, which result in performance characteristics similar to a V engine. But it is also considered a flat engine because of its shape. On the other hand, some V-twin engines which have none of the typical V engine crankshaft design features and consequent performance characteristics are also regarded as V engines, purely because of their shape. Similarly, the Volkswagen VR6 engine is a hybrid of the V engine and the straight engine, and can not be definitively labeled as either. The names W engine and rotary engine have each been used for several unconnected designs. The H-4 and H-6 engines produced by Subaru are not H engines at all, but boxer engines.

Categorisation by piston motion

Engine types include:

• Single cylinder engines
• Inline engine designs:
  • Straight engine, with all of the pistons are placed in a single row
  • V engine, with two banks of cylinders at an angle, most commonly 60 or 90 degrees.
  • Flat engine, two banks of cylinders directly opposite each other on either side of the crankshaft.
  • H engine, two crankshafts.
  • W engine. Can be both 3 banks and 4 banks.
  • Square engine.
  • Opposed piston engine, with multiple crankshafts, an example being:
    • Delta engines, with three banks of cylinders and three crankshafts
  • U engine, two separate straight engines with crankshafts linked by a central gear.
  • X engine.

• Radial designs, including most:
  • Rotary engine designs.

• Pistonless rotary engines, notably:
  • Wankel engine.

Other categorizations

The majority of four stroke engines have poppet valves although some aircraft engines had sleeve valves. Valves may be located in the cylinder block (side valves) or in the cylinder head (overhead valves). Modern engines are invariably of the latter design. There may be two, three or four valves per cylinder. ie exhaust and inlet valves.

Poppet valves are opened by means of a camshaft which revolves at half the crankshaft speed. This can be either chain, gear or toothed belt driven from the crankshaft and can be located in the crankcase (where it may serve one or more bank of cylinders) or in the cylinder head. There may be one or two camshafts in a cylinder head. If the camshaft is located in the crankcase, a valve train of pushrods and rockers will be required to operate overhead valves. With the side valve arrangement, the valve stems rested on the camshaft. This is a very simple mechanical arrangement but the gas flows within the cylinder head with the side valve arrangement is very poor. If the camshaft(s) is/are located in the cylinder head, the valvetrain will be shorter, no pushrods being required. Some single camshaft designs, still have a rocker. This facilates adustment of mechanical clearances. If there are two camshafts in the cylinder head, (DOHC, double overhead cam)the cams normally bear directly on to the valve stems. This is the usual arrangement for a four-valves-per-cylinder design. This latter arrangement is the most inertia free, allows the most unimpeded gas flows in the engine and is the usual arrengement for high performance automobile engines. It also permits the spark plug to be located in the centre of the cylinder head, which promotes better combustion characteristics. Very large engines eg marine engines can have either extra camshafts or extra lobes on the camshaft to enable the engine to run in either direction.