Car, truck and SUV manufacturers use a wide range of engine types and sizes to power the vehicles people use every day. From the 4-cylinder engines you can find in compact cars, to the powerful V8, V10 and V12 engines in sports cars, each engine relies on precise engineering and a number of different components, all tuned to the right specifications, to operate properly and efficiently.
Layout
The vast majority of 4-cylinder engines in passenger cars use an inline cylinder layout. This means that the engine block places all four cylinders in a single row. The major alternative to an inline layout is a V-layout, which gives V6 and V8 engines their designation. While V4 engines do exist, they are rare in automobiles.
Cars can use 4-cylinder engines in a number of positions. Some vehicles use a rear-engine, rear-wheel-drive layout, with the 4-cylinder engine mounted behind the passenger compartment. Others have the 4-cylinder engine in the front, under the hood. When a front-engine car features rear-wheel drive, the 4-cylinder engine is mounted in a longitudinal position, running parallel to the length of the car. In front-engine/front-wheel-drive cars, the engine takes a transverse position, running perpendicular to the length of the car, or side-to-side under the hood.
Displacement
A 4-cylinder engine's displacement measures the total volume of its four combustion chambers, or cylinders. Automakers commonly advertise an engine's size as its total displacement, either in cubic inches or liters. You can compute an engine's displacement using its bore, or the width of each cylinder, with the stroke, or the functional depth of each chamber, and multiplying the result by four for the number of cylinders. Most 4-cylinder engines have a displacement of less than three liters, and many are below two liters.
Valves
In a 4-cylinder engine, each of the four combustion chambers needs at least one fuel valve, to allow fuel and air in, and one exhaust valve, to expel unburned fuel and gasses after combustion. The smallest number of valves a 4-cylinder engine can have is eight, with two valves per cylinder. However, some 4-cylinder engines use three, or even four, valves per cylinder for a total of 12 or 16. Valve layouts vary from one automaker to another, and don't necessarily represent more power or greater efficiency.
Output
Horsepower is the major metric for ranging an engine's ability to produce power. A 4-cylinder engine produces a range of horsepower at different engine speeds, with automakers generally advertising the engine's peak horsepower, even if it only occurs within a narrow range of very high engine speeds. Torque is another important measurement, referring to how much turning power the engine produces at a car's wheels. A 4-cylinder engine with a low horsepower rating but a reasonable amount of torque should deliver ample power in most driving conditions.
Aspiration
Aspiration refers to the process through which an engine receives air, which contains the oxygen necessary for combustion. A naturally aspirated engine draws in air on its own through a four-stroke cycle of intake, compression, combustion and exhaust. However, to compensate for the small displacement and low power output of some 4-cylinder engines, automakers may add a turbocharger or supercharger. These devices force additional air into the engine for a more powerful combustion stroke and, ultimately, more power. Turbocharged 4-cylinder engines have higher horsepower ratings than similar engines that are naturally aspirated.
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