The inline-four engine or straight-four engine is a type of inline internal combustion four-cylinder engine with all four cylinders mounted in a straight line, or plane along the crankcase. The single bank of cylinders may be oriented in either a vertical or an inclined plane with all the pistons driving a common crankshaft. Where it is inclined, it is sometimes called a slant-four. In a specification chart or when an abbreviation is used, an inline-four engine is listed either as I4 or L4 (for longitudinal, to avoid confusion between the digit 1 and the letter I).

The inline-four layout is in perfect primary balance and confers a degree of mechanical simplicity which makes it popular for economy cars.^[1]However, despite its simplicity, it suffers from a secondary imbalance which causes minor vibrations in smaller engines. These vibrations become more powerful as engine size and power increase, so the more powerful engines used in larger cars generally are more complex designs with more than four cylinders.

Today almost all manufacturers of four-cylinder engines for automobiles produce the inline-four layout, with Subaru and Porsche 718^[2] flat-four engines being notable exceptions, and so four-cylinder is usually synonymous with and a more widely used term than inline-four. The inline-four is the most common engine configuration in modern cars, while the V6 engine is the second most popular.^[3] In the late 2000s (decade), due to stringent government regulations mandating reduced vehicle emissions and increased fuel efficiency, the proportion of new vehicles sold in the U.S. with four-cylinder engines (largely of the inline-four type) rose from 30 percent to 47 percent between 2005 and 2008, particularly in mid-size vehicles where a decreasing number of buyers have chosen the V6 performance option

Power Stroke is a name used by a family of diesel engines for trucks produced by Ford Motor Company since 1994. Along with its use in the Ford F-Series (including the Ford Super Duty trucks), applications include the Ford E-Series, Ford Excursion, and Ford LCF commercial truck; the name was also used for a diesel engine used in South American production of the Ford Ranger.

From 1994, the Power Stroke engine family existed as a re-branding of engines produced by Navistar International, sharing engines with its medium-duty truck lines. Since the 2010 introduction of the 6.7L PowerStroke V8, Ford has designed and produced its own diesel engines. During its production, the PowerStroke engine range has been marketed against large-block V8 (and V10) gasoline engines along with the General Motors Duramax V8 and the Dodge Cummins B-Series inline-six.

The RB engine is a 2.0–3.0 L straight-6 four-stroke petrol/gasoline engine from Nissan, produced from 1985-2004.

Both SOHC and DOHC versions have an aluminium head. The SOHC versions have 2 valves per cylinder and the DOHC versions have 4 valves per cylinder; each cam lobe moves only one valve. All RB engines have belt-driven cams and a cast iron block. Most turbo models have an intercooled turbo (the exceptions being the single cam RB20ET & RB30ET engines), and most have a recirculating factory blow off valve (the exceptions being when fitted to Laurels and Cefiros) to reduce compressor surge when the throttle quickly closes. The Nissan RB Engine is derived from the six cylinder Nissan L20A engine which has the same bore and stroke as the RB20. All RB engines were made in Yokohama, Japan where the new VR38DETT is now made. Some RB engines were rebuilt by Nissan’s NISMO division at the Omori Factory in Tokyo as well. All Z-Tune Skylines were rebuilt at the Omori Factory.

VTEC (Variable Valve Timing & Lift Electronic Control) is a syste m developed by Honda which was said 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 (or occasionally three) camshaft profiles and hydraulically selects between profiles. It was invented by Honda engineer Ikuo Kajitani.^[1][2] It is distinctly different from standard VVT (variable valve timing) systems which only change valve timing and do not change the camshaft profile or valve lift in any way.

SOHC: Is where the camshaft is inside the cylinder head

DOHC: Is where there are 2 camshafts inside the cylinder head.

Camshafts:In internal combustion engines with pistons, the camshaft is used to operate poppet valves. It consists of a cylindrical rod running the length of the cylinder bank with a number of oblong lobes protruding from it, one for each valve. The cam lobes force the valves open by pressing on the valve, or on some intermediate mechanism, as they rotate.

Engine Configurations:

Engine configuration is an engineering term for the layout of the major components of a reciprocating piston internal combustion engine. These components are the cylinders and crankshafts in particular but also, sometimes, the camshaft(s).

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. The Subaru H-4 and H-6 designs are so named because they are horizontally opposed pistons.

Engine types include:

• Single-cylinder engines
• Inline engine designs:
  • Straight engine, with all of the cylinders placed in a single row
    • U engine, two separate straight engines with crankshafts linked by a central gear.
      • The square four is a U engine where the two straight engines have two cylinders each.
  • 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 separate flat engines with crankshafts linked by a central gear.
  • W engine. Combination of V and straight, giving 3 banks, or two V’s intertwined giving 4 banks.
  • Opposed piston engine, with multiple crankshafts, an example being:
    • Delta engines, with three banks of cylinders and three crankshafts
  • X engine.
• Radial designs, including most:
  • Rotary engine designs. Almost only seen on World War I aircraft.
• Pistonless rotary engines, notably:
  • Wankel engine.

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 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 Group VR6 engine is a hybrid of the V engine and the straight engine, and can not be definitively labeled as either.

In automotive engineering, an exhaust manifold collects the exhaust gases from multiple cylinders into one pipe.

Exhaust manifolds are generally simple cast iron or stainless steel units which collect engine exhaust gas from multiple cylinders and deliver it to the exhaust pipe. For many engines, there are aftermarket tubular exhaust manifolds known as headers.

Nitrous: In vehicle racing, nitrous oxide (often referred to as just “nitrous”) allows the engine to burn more fuel by providing more oxygen than air alone, resulting in a more powerful combustion.^{[citation needed]} The gas is not flammable at a low pressure/temperature, but it delivers more oxygen than atmospheric air by breaking down at elevated temperatures. Therefore, it often is mixed with another fuel that is easier to deflagrate. Nitrous oxide is a strong oxidant, roughly equivalent to hydrogen peroxide, and much stronger than oxygen gas.

Hydraulics: a system added to a car which can raise or lower a car on command. Probably by the means of using a liquid to move hydraulic pistons.

A crankshaft—related to crank—is a mechanical part able to perform a conversion between reciprocating motionand rotational motion. In a reciprocating engine, it translates reciprocating motion of the piston into rotational motion; whereas in a reciprocating compressor, it converts the rotational motion into reciprocating motion. In order to do the conversion between two motions, the crankshaft has “crank throws” or “crankpins”, additional bearing surfaces whose axis is offset from that of the crank, to which the “big ends” of the connecting rods from each cylinder attach.

It is typically connected to a flywheel to reduce the pulsation characteristic of the four-stroke cycle, and sometimes a torsional or vibrational damper at the opposite end, to reduce the torsional vibrations often caused along the length of the crankshaft by the cylinders farthest from the output end acting on the torsional elasticity of the metal.

A flywheel is a mechanical device specifically designed to efficiently store rotational energy. Flywheels resist changes in rotational speed by their moment of inertia. The amount of energy stored in a flywheel is proportional to the square of its rotational speed. The way to change a flywheel’s stored energy is by increasing or decreasing its rotational speed by applying a torquealigned with its axis of symmetry,

Common uses of a flywheel include:

• Smoothing the power output of an energy source. For example, flywheels are used in reciprocating engines because the active torque from the individual pistons is intermittent.
• Energy storage systems
• Delivering energy at rates beyond the ability of an energy source. This is achieved by collecting energy in a flywheel over time and then releasing it quickly, at rates that exceed the abilities of the energy source.
• Controlling the orientation of a mechanical system, gyroscope and reaction wheel

Flywheels are typically made of steel and rotate on conventional bearings; these are generally limited to a maximum revolution rate of a few thousand RPM.^[1] High energy density flywheels can be made of carbon fiber composites and employ magnetic bearings, enabling them to revolve at speeds up to 60,000 RPM (1 kHz)

Torque is part of the basic specification of an engine: the power output of an engine is expressed as its torque multiplied by its rotational speed of the axis. Internal-combustion engines produce useful torque only over a limited range of rotational speeds (typically from around 1,000–6,000 rpm for a small car). The varying torque output over that range can be measured with a dynamometer, and shown as a torque curve.

Steam engines and electric motors tend to produce maximum torque close to zero rpm, with the torque diminishing as rotational speed rises (due to increasing friction and other constraints). Reciprocating steam engines can start heavy loads from zero RPM without a clutch.

Horsepower: A unit of measurement of power (the rate at which work is done). There are many different standards and types of horsepower. Two common definitions being used today are the mechanical horsepower (or imperial horsepower), which is 745.7 watts, and the metric horsepower, which is approximately 735.5 watts.

Indicated horsepower

Indicated horsepower (ihp) is the theoretical power of a reciprocating engine if it is completely frictionless in converting the expanding gas energy (piston pressure × displacement) in the cylinders. It is calculated from the pressures developed in the cylinders, measured by a device called an engine indicator – hence indicated horsepower. As the piston advances throughout its stroke, the pressure against the piston generally decreases, and the indicator device usually generates a graph of pressure vs stroke within the working cylinder. From this graph the amount of work performed during the piston stroke may be calculated.

Indicated horsepower was a better measure of engine power than nominal horsepower (nhp) because it took account of steam pressure. But unlike later measures such as shaft horsepower (shp) and brake horsepower (bhp), it did not take into account power losses due to the machinery internal frictional losses, such as a piston sliding within the cylinder, plus bearing friction, transmission and gear box friction, etc.

Brake horsepower

Brake horsepower (bhp) is the power measured at the crankshaft just outside the engine, before the losses of power caused by the gearbox and drive train.

In Europe, the DIN 70020 standard tests the engine fitted with all ancillaries and exhaust system as used in the car. The older American standard (SAE gross horsepower, referred to as bhp) used an engine without alternator, water pump, and other auxiliary components such as power steering pump, muffled exhaust system, etc., so the figures were higher than the European figures for the same engine. The newer American standard (referred to as SAE net horsepower) tests an engine with all the auxiliary components (see “Engine power test standards” below).

Brake refers to the device which was used to load an engine and hold it at a desired rotational speed. During testing, the output torque and rotational speed were measured to determine the brake horsepower. Horsepower was originally measured and calculated by use of the “indicator diagram” (a James Watt invention of the late 18th century), and later by means of a Prony brake connected to the engine’s output shaft. More recently, an electrical brake dynamometer is used instead of a Prony brake. Although the output delivered to the drive wheels is less than that obtainable at the engine’s crankshaft, use of a chassis dynamometer gives an indication of an engine’s “real world” horsepower after losses in the drive train and gearbox.

Shaft horsepower

Shaft horsepower (shp) is the power delivered to a propeller shaft, a turbine shaft – or to an output shaft of an automotive transmission.^[28] This shaft horsepower can be measured with a torque (torsion) meter, or estimated from the horsepower at the crankshaft and a standard figure for the losses in the transmission (typical figures are around 10%). Shaft horsepower is a common rating for jet engines, industrial turbines, and some marine applications. Reciprocating internal-combustion automobile engines are rated instead in the USA by SAE certified net power, which is measured at the engine’s crankshaft, and so does not account for losses in the transmission.

Wheel horsepower

Motor vehicle dynamometers can measure wheel horsepower (whp), which is the effective, true horsepower delivered to the driving wheel(s), representing the actual power available to accelerate the vehicle after all losses in the drive train, and all parasitic losses such as pumps, fans, alternator, muffled exhaust, etc. The vehicle is generally attached to the dynamometer and accelerates a large roller and Power Absorbing Unit which is driven by the vehicle’s drive wheel(s). The actual power is then computer calculated based on the rotational inertia of the roller, its resultant acceleration rates and power applied by the Power Absorbing Unit. Some motor vehicle (and motorbike) dynamometers can also be purely inertia-based where the power output is calculated from measuring the acceleration of a roller drum with a known rotational inertia and known parasitic frictional losses of the roller drum’s bearings.

The diesel engine (also known as a compression-ignition or CI engine), named after Rudolf Diesel, is an internal combustion engine in which ignition of the fuel which is injected into the combustion chamber is caused by the elevated temperature of the air in the cylinder due to mechanical compression (adiabatic compression). Diesel engines work by compressing only the air. This increases the air temperature inside the cylinder to such a high degree that atomised diesel fuel that is injected into the combustion chamber ignites spontaneously. This contrasts with spark-ignition engines such as a petrol engine (gasoline engine) or gas engine (using a gaseous fuel as opposed to petrol), which use a spark plug to ignite an air-fuel mixture. In diesel engines, glow plugs (combustion chamber pre-warmers) may be used to aid starting in cold weather, or when the engine uses a lower compression-ratio, or both. The original diesel engine operates on the “constant pressure” cycle of gradual combustion and produces no audible knock.

A spark plug (sometimes, in British English, a sparking plug,^[1] and, colloquially, a plug) is a device for delivering electric current from an ignition system to the combustion chamber of a spark-ignition engine to ignite the compressed fuel/air mixture by an electric spark, while containing combustion pressure within the engine. A spark plug has a metal threaded shell, electrically isolated from a central electrode by a porcelaininsulator. The central electrode, which may contain a resistor, is connected by a heavily insulated wire to the output terminal of an ignition coil or magneto. The spark plug’s metal shell is screwed into the engine’s cylinder head and thus electrically grounded. The central electrode protrudes through the porcelain insulator into the combustion chamber, forming one or more spark gaps between the inner end of the central electrode and usually one or more protuberances or structures attached to the inner end of the threaded shell and designated the side, earth, or groundelectrode(s).