Engine configuration

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The engine configuration describes the fundamental operating principles by which internal combustion engines are categorized.


Piston engines are often categorized by their cylinder layout, valves and camshafts. Wankel engines are often categorized by the number of rotors present. Gas turbine engines are often categorized into turbojets, turbofans, turboprops and turboshafts.

Types of cylinder layouts

Single cylinder engines

Straight / inline engines

1928-1942 Indian Four straight-4 motorcycle engine Indian 4 engine manifold side.jpg
1928-1942 Indian Four straight-4 motorcycle engine

Straight engines, also known as inline engines, have all cylinders aligned in one row along the crankshaft with no offset. When a straight engine is mounted at an angle, it is sometimes called a "slant engine". Types of straight engines include:

V engines

V6 engine IC engine.JPG
V6 engine

V engines, also known as Vee engines, have the cylinders aligned in two separate planes or 'banks', so that they appear to be in a "V" when viewed along the axis of the crankshaft. Types of V engines include:

Flat engines

Douglas flat-twin motorcycle engine Douglas motorcycle engine, Abergavenny steam rally 2012.jpg
Douglas flat-twin motorcycle engine

Flat engines, also known as "horizontally-opposed" or "boxer" engines, have the cylinders arranged in two banks on either side of a single crankshaft. Types of flat engines include:

Opposed-piston engines

An opposed-piston engine is like a Flat/boxer engine in that pairs of pistons are co-axial but rather than sharing a crankshaft, instead share a single combustion chamber per pair of pistons. The crankshaft configuration varies amongst opposed-engine designs. One layout has a flat/boxer engine at its center and adds an additional opposed-piston to each end so there are two pistons per cylinder on each side.

W engines

W engines have the cylinders in a configuration in which the cylinder banks resemble the letter W, in the same way those of a V engine resemble the letter V. Types of W engines include:

X engines

An X engine is essentially two V engines joined by a common crankshaft. A majority of these were existing V-12 engines converted into an X-24 configuration.

U engines

U engines consist of two separate straight engines (complete with separate crankshafts) joined by gears or chains. Most U engines have four-cylinders (i.e. two straight-two engines combined), such as square four engines and tandem twin engines

H engines

Similar to U engines, H engines consist of two separate flat engines joined by gears or chains. H engines have been produced with between 4 and 24 cylinders.

Horizontal K type engine

Horizontal K-Type engine configuration proposed and analyzed by Rushiraj Kadge. This engine boasts the following benefits:

Better balanced. This means more power can be extracted from Horizontal K configuration. The proposed configuration has least frictional losses. CG height of proposed configuration is less which denotes higher stability Mass of proposed configuration is less with same number of reciprocating and rotating masses. This is due to the reduced length of crankshaft. If power is assumed to be constant, then Power-to-weight ratio of proposed configuration is more. [1]

Radial engines

A radial engine has a single crankshaft with cylinders arranged in a planar star shape around the same point on the crankshaft. This configuration was commonly used with 5 air-cooled cylinders in aircraft.

Delta engines

A Delta Engine has three (or its multiple) cylinders having opposing pistons, aligned in three separate planes or 'banks', so that they appear to be in a Δ when viewed along the axis of the main-shaft. A notable example of this type of layout is the Napier Deltic.

Other layouts

Less common configurations include the Swashplate engine with the K-Cycle engine being one where pairs of pistons are in an opposed configuration sharing a cylinder and combustion chamber.


The majority of four stroke engines have poppet valves, although some aircraft engines have 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, four or five valves per cylinder, with the intake valves outnumbering the exhaust valves in case of an odd number. Interference engines are such engines in which a valve could collide with a piston if the valve timing was incorrect.


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 banks of cylinders) or in the cylinder head.

If the camshaft is located in the crankcase, a valve train of pushrods and rocker arms will be required to operate overhead valves. Mechanically simpler are side valves, where the valve stems rested directly on the camshaft However, this gives poor gas flows within the cylinder head as well as heat problems and fell out of favor for automobile use, see flathead engine .

The majority of modern automobile engines place the camshaft on the cylinder head in an overhead camshaft (OHC) design. There may be one or two camshafts in the cylinder head; a single camshaft design is called single overhead camshaft (SOHC). A design with two camshafts per cylinder head is called double overhead camshaft (DOHC). Note that the camshafts are counted per cylinder head, so a V engine with one camshaft in each of its two-cylinder heads is still an SOHC design, and a V engine with two camshafts per cylinder head is DOHC, or informally a "quad cam" engine. [2] [3]

With overhead camshafts, the valvetrain will be shorter and lighter, as no pushrods are required. Some overhead camshaft designs still have rocker arms; this facilitates adjustment of mechanical clearances.

A four valves per cylinder design usually has two valves for intake and two for exhaust, which requires two camshafts per cylinder bank. If there are two camshafts in the cylinder head, the cams can sometimes bear directly on cam followers on the valve stems (tappets). The cam followers aid in noise reduction, dampened vibration, shock absorption and the carrying of axial load. [4] [5] This latter arrangement is the most inertia free, allows the most unimpeded gas flows in the engine and is the usual arrangement for high performance automobile engines. It also permits the spark plug to be located in the center of the cylinder head, which promotes better combustion characteristics. Beyond a certain number of valves, the effective area covered decreases, so four is the common-most number. Odd numbers of valves necessarily means the intake or exhaust side must have one valve more. In practice this is invariably the intake valves - even in even-numbered head designs, inlet valves are often larger in size than exhaust.

Very large engines (e.g. marine engines) can have either extra camshafts or extra lobes on the camshaft to enable the engine to run in either direction. Furthermore, other manipulations of valves can be used for e.g. engine braking, such as in a Jake brake.

A disadvantage of overhead cams is that a much longer chain (or belt) is needed to drive the cams than with a camshaft located in the cylinder block, usually a tensioner is also needed. A break in the belt may destroy the engine if pistons touch open valves at top dead center.

Wankel (rotary) engines

Wankel engines (sometimes called 'rotary engines') can be classified based on the number of rotors present. Most production Wankel engines have two rotors, however engines with one, three and four rotors have also been produced. [6] [7] Wankel engines can also be classified based on whether they are naturally aspirated or turbocharged.

Most Wankel engines are fueled by petrol, however prototype engines running on diesel and hydrogen have been investigated.

Gas turbine engines

Gas turbine engines— mostly used for aircraft— are usually separated into the following categories:

Related Research Articles

Poppet valve Type of valve

A poppet valve is a valve typically used to control the timing and quantity of gas or vapor flow into an engine.

Camshaft mechanical component that converts rotational motion to reciprocal motion

A camshaft is a rotating object— usually made of metal— that contains pointed cams, which converts rotational motion to reciprocal motion. Camshafts are used in internal combustion engines, mechanically controlled ignition systems and early electric motor speed controllers. Camshafts in automobiles are made from steel or cast iron, and are a key factor in determining the RPM range of an engine's power band.

Cylinder head Component of a cylinder of an internal combustion engine

In an internal combustion engine, the cylinder head sits above the cylinders on top of the cylinder block. It closes in the top of the cylinder, forming the combustion chamber. This joint is sealed by a head gasket. In most engines, the head also provides space for the passages that feed air and fuel to the cylinder, and that allow the exhaust to escape. The head can also be a place to mount the valves, spark plugs, and fuel injectors.

Hemispherical combustion chamber

A hemispherical combustion chamber is a type of combustion chamber in a reciprocating internal combustion engine with a domed cylinder head in the approximate shape of a hemisphere. An engine featuring this type of hemispherical chamber is known as a hemi engine.

VTEC Engine system

VTEC is a system developed by Honda to improve the volumetric efficiency of a four-stroke internal combustion engine, resulting in higher performance at high RPM, and lower fuel consumption at low RPM. The VTEC system uses two camshaft profiles and hydraulically selects between profiles. It was invented by Honda engineer Ikuo Kajitani. It is distinctly different from standard VVT systems which change only the valve timings and do not change the camshaft profile or valve lift in any way.

Chrysler 1.8, 2.0 & 2.4 engine Motor vehicle engine

The Chrysler 1.8, 2.0, and 2.4 are inline-4 engines designed originally for the Dodge and Plymouth Neon compact car. These engines were loosely based on their predecessors, the Chrysler 2.2 & 2.5 engine, sharing the same 87.5 mm (3.44 in) bore. The DOHC head was developed by Chrysler with input from the Chrysler-Lamborghini team that developed the Chrysler/Lamborghini Formula 1 V12 engine in the early 1990s.

Ford Modular engine Engine family produced by Ford Motor Company

The Ford Modular engine is Ford Motor Company's overhead camshaft (OHC) V8 and V10 gasoline-powered small block engine family. Despite popular belief that the Modular engine family received its moniker from the sharing of engine parts across numerous Ford vehicle platforms, in reality, the Modular engine family was named as such by Ford Motor Company for the new “modular approach” to the setup of tooling and casting stations in the Windsor and Romeo engine manufacturing plants.

Overhead camshaft engine Valvetrain configuration

An overhead camshaft (OHC) engine is a piston engine where the camshaft is located in the cylinder head above the combustion chamber. This contrasts with earlier overhead valve engines (OHV), where the camshaft is located below the combustion chamber in the engine block.

Overhead valve engine Type of piston engine

An overhead valve (OHV) engine is a piston engine whose valves are located in the cylinder head above the combustion chamber. This contrasts with earlier flathead engines, where the valves were located below the combustion chamber in the engine block.

Saturn I4 engine Motor vehicle engine

The powerplant used in Saturn S-Series automobiles was a straight-4 aluminum piston engine produced by Saturn, a subsidiary of General Motors. The engine was only used in the Saturn S-series line of vehicles from 1991 through 2002. It was available in chain-driven SOHC or DOHC variants.

Multi-valve Type of car engine

In automotive engineering a multi-valve or multivalve engine is one where each cylinder has more than two valves. A multi-valve engine has better breathing and may be able to operate at higher revolutions per minute (RPM) than a two-valve engine, delivering more power.


A tappet is most commonly a component in an internal combustion engine which converts the rotating motion of the camshaft into linear motion of the valves, either directly or indirectly.

The Honda F-Series engine was considered Honda's "big block" SOHC inline four, though lower production DOHC versions of the F-series were built. It features a solid iron or aluminum open deck cast iron sleeved block and aluminum/magnesium cylinder head.

Motorcycle engine Engine that powers a motorcycle

A motorcycle engine is an engine that powers a motorcycle. Motorcycle engines are typically two-stroke or four-stroke internal combustion engines, but other engine types, such as Wankels and electric motors, have been used.

Valvetrain Mechanical system

A valvetrain or valve train is a mechanical system that controls the operation of the intake and exhaust valves in an internal combustion engine. The intake valves control the flow of air/fuel mixture into the combustion chamber, while the exhaust valves control the flow of spent exhaust gasses out of the combustion chamber once combustion is completed.

The cam-in-block valvetrain layout of piston engines is one where the camshaft is placed within the cylinder block, usually beside and slightly above the crankshaft in a straight engine or directly above the crankshaft in the V of a V engine. This contrasts with an overhead camshaft (OHC) design which places the camshafts within the cylinder head and drives the valves directly or through short rocker arms.

The Mazda FE-DOHC was the DOHC variant of the FE. The official Mazda engine codes are FE-DE and FE-ZE, depending on output level. It is still commonly called the FE3 because of its head castings. The FE-DOHC shares the same dimensions as the original FE-SOHC, including the square 86 mm bore × stroke and it has an ideal 1.74 rod/stroke ratio. The FE-DOHC is usually identified by a gold-coloured cam cover, however not always. There were at least five different FE-DOHC engines available with various compression ratio, camshaft and ECU tuning combinations, however none were fitted with a turbocharger from the factory. Despite this, the FE-DOHC is already built for turbo with large forged connecting rods, large journal dimensions, oil cooler, piston oilers, web-stiffened block with main girdles. This robust engine design is a favourite of tuners who are aware of its capability because it already has a high-power capacity perfect for custom turbo jobs. As much as 600 whp has been seen on a stock engine. The common FE-DOHC crankshaft is cast while the forged crankshaft is fitted to the aluminum sump engines with both the main bearing braces and the main bearing girdle plate. In European 10.0:1 compression, non-catalytic trim, the FE-DOHC produces 148 ps (108 kW) at 6000 rpm and 133 lb/ft at 4000 rpm. The 9.2:1 compression, catalytic converter version produces 140 ps. The Japanese domestic market variants produce anywhere between 145 ps and 165 ps. The only vehicle with 165ps was the 96-97 Capellas Wagons, FX or FX Cruising. They had different tail lights to the earlier wagons.


  1. Kadge, R. and Thirumalini, S., "Investigation on Design of a New Horizontal K-Type Configuration for Internal Combustion Engine," SAE Int. J. Engines 14(1):29-45, 2021, https://doi.org/10.4271/03-14-01-0003.
  2. "Camshaft Basics". www.oregoncamshaft.com. Retrieved 2016-02-05.
  3. "OHV, OHC, SOHC and DOHC (twin cam) engine - Automotive illustrated glossary". Samarins.com. Retrieved 2016-02-05.
  4. "How Car Engines Work". HowStuffWorks. Retrieved 2016-02-05.
  5. "Cam Follower Bearings On Emerson Bearing". products.emersonbearing.com. Retrieved 2016-02-05.
  6. "Technically Interesting: Dr. Wankel's Quad-Rotor Mercedes SL". www.bringatrailer.com. 21 March 2018. Retrieved 31 August 2019.
  7. "How a Four-Rotor Wankel Engine Works". www.roadandtrack.com. 23 November 2016. Retrieved 31 August 2019.