Today’s automobile engines work on a reciprocating movement known as the 4-stroke cycle, or Otto cycle, named after the person who built the first working prototype. The cycle is made up of the intake, compression, combustion and exhaust strokes. This is the basic operation of most, if not all, automotive piston engines available today.
For a V8 engine to produce power, fuel from the tank is pumped to high pressure into injector rails, to which the engine’s fuel injectors are connected. Operated by the camshafts, the intake valves open during the intake stroke to allow the air and fuel mixture to enter the engine’s combustion chamber from the intake manifold, pulled by partial vacuum as the piston moves down and pushed by atmospheric pressure. The exhaust valves, also being actuated by the cams, are closed during this phase. With the piston at the bottom of its stroke, it now moves up the cylinder (this action being initiated by the piston and rotating crankshaft tied together by a connecting rod) to begin the compression stroke. The camshafts are also connected to the crankshaft, commonly by a chain drive and in the compression stroke, the cam lobes are positioned in such a way that both intake and exhaust valves are now closed. As the piston moves up towards the combustion chamber, the air/fuel mixture is pressurized. Just before the end of the compression stroke, the air/fuel mixture is ignited by the spark plug. The combustion that occurs causes a rise in temperature and pressure to expand the gases that force the piston downward again. As the gases expand through the cylinder and bottom out the piston through its range of travel, the piston, because of its connection to the crankshaft, moves up again and forces the burnt gases out of the cylinder, where the camshaft has opened the intake valves, and into the exhaust system. This is the exhaust stroke and at the top of the piston’s travel, the intake stroke begins the cycle again for that particular cylinder.
This is a very basic description of the operation of a 4-stroke engine. In a V8, the eight cylinders are mounted in two banks of four cylinders with a crankcase beneath the two banks, where the crankshaft is driven by all eight pistons. All multi-cylinder engines have a firing order, which is the sequence of the power delivery of each individual cylinder. Modern V8s from GM and Ford have 1-8-7-2-6-5-4-3 as their firing order. The firing order is determined in the design stage of an engine and is critical to minimizing vibration, achieving long engine life and having a smooth-running engine for user comfort.
Of course, all engines have auxiliary systems to support the basic operation of an engine, such as the cooling system, lubrication system, intake/exhaust systems, ignition systems, electrical system and the engine management system. Although it all sounds very complex and actually is, a basic understanding of the workings of an engine will often spell the difference between what a crooked mechanic is trying to sell you and knowing the limit, or extent, of the repair that actually has to be done.