Car engines for modern cars are all internal combustion engines and are in general run by petroleum-based fuels, whether gasoline or diesel. Although there are two- and four-stroke internal combustion engines, the use of the four-stroke cycle for car engines is universal. Engines for automotive use come in inline, horizontally-opposed, V and rotary configurations. In all but the last configuration, these engines are driven by pistons rotating a crankshaft connected to a transmission system.

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Petrol engine cars have the most configurations and engine types. In Europe and Australasia, diesel engine cars have a loyal following unlike in North America, where diesel engine cars are normally shunned and their use is more often found in commercial vehicles. Diesel engines are also known as compression-ignition engines, because the ignition of the fuel mixture is initiated by the heat of compressing the air-fuel mixture. Diesel engines do not have an electrical ignition system like that found in petrol engine cars. Because of its high compression ratio (typically in the 16:1 to 22:1 range) diesel engines have the highest thermal efficiency of all internal combustion engines. In terms of fuel efficiency and operating cost, diesel-powered cars are typically cheaper to run and maintain. Furthermore, diesel engines are built stronger, so engine life is almost twice that of gasoline-powered engines. Diesel engines lend themselves well to turbo- or supercharging for this very reason. Diesel engines are not known for their high horsepower ratings. Rather, they excel in producing torque at low rpm, which is more desirable when pulling loads or going up hilly or mountainous terrain.

Technology for diesel engines has not been stagnant, however. In the last few years, winners of the prestigious Le Mans 24-hour endurance race have been powered by diesel engines. It is only a matter of time before the technology used in these competition diesel engines trickles down to mass production applications. Although diesel engines have more particulates in their exhaust, diesel engines actually produce less carbon monoxide, compared to petrol engines. Most diesel engines in use today use an inline or V configuration.

Modern petrol fuelled car engines have become so sophisticated that computers and electronic sensors are now needed to enable them to run at peak efficiency. Before the fuel crisis of the 1970s, petrol was cheap and plentiful and petrol engines tended to be inefficient, wasteful of fuel and polluting the atmosphere with the rich fuel mixtures that engineers tuned carburetors with. The oil crisis precipitated by OPEC together with government mandates to increase fuel efficiency and reduce pollution forced car manufacturers to adopt technologies that would make engines cleaner-burning and much more fuel-efficient.

Japanese manufacturers were able to make tremendous inroads into major automotive markets because they were able to combine the technologies necessary to make fuel-efficient cars. Where automakers like Ford and GM generally stuck to their large displacement engines, Toyota and Honda produced tiny 1600 cc, or even 1100 cc engines to power their cars using throttle-body fuel injection systems that were advanced for their time but crude by todays standards.

Most car engines today use inline-4 and V6 configurations in different displacements. V8s and engines with up to 16 cylinders in a V or W configuration are also being used but these are seen in lower-volume, high-performance luxury cars such as those from Mercedes, BMW, Audi and Ferrari. Notably however, Subaru has made its EJ-series engine a world standard in the use of a horizontally-opposed engine (also called a boxer engine) in mass-produced vehicles. While Ferrari and Porsche have both been producing boxer engines for decades, Subaru brought efficient, reliable and high-performance boxer engines to the masses.

Most especially in the past decade, forced induction systems (turbochargers and superchargers) have seen favour with manufacturers because they offer huge horsepower increases while allowing the use of smaller displacement engines. This has the dual benefits of improving fuel consumption and reducing the pollution generated by car engines. In the face of continually tightening government regulations, this has sometimes proven to be the only way to provide cars with adequate performance with the requisite fuel economy.