The firing order of an internal combustion engine is the sequence of ignition for the cylinders. In a spark ignition (e.g. gasoline/petrol) engine, the firing order corresponds to the order in which the spark plugs are operated. In a diesel engine, the firing order corresponds to the order in which fuel is injected into each cylinder. Four-stroke engines must also time the valve openings relative to the firing order, as the valves do not open and close on every stroke. Firing order affects the vibration, sound and evenness of power output from the engine and heavily influences crankshaft design. Cylinder numbering Numbering systems for car engines The numbering system for cylinders is generally based on the cylinder numbers increasing from the front to the rear of an engine (See engine orientation below). However, there are differences between manufacturers in how this is applied; some commonly used systems are as listed below. Straight engine Cylinders numbered from front (#1 cylinder) to rear. V engine The frontmost cylinder is usually #1, however there are two common approaches: Numbering the cylinders in each bank sequentially (e.g. 1-2-3-4 along the left bank and 5-6-7-8 along the right bank). This approach is typically used by V8 engines from Audi, Ford and Porsche. Numbering the cylinders based on their position along the crankshaft (e.g. 1-3-5-7 along the right bank and 2-4-6-8 along the left bank). This approach is typically used by V8 engines from General Motors, and Chrysler. The selection of whether the #1 cylinder is on the left bank or right bank usually depends on which bank is closer to the front of the crankshaft. However, the Ford Flathead V8 and Pontiac V8 engine actually have the #1 cylinder behind the cylinder from the opposite bank. This was done so that all Ford engines would have cylinder #1 on the right bank and all Pontiac engines would have cylinder #1 on the left bank, to simplify the process of identifying the cylinders. Radial engine The cylinders are numbered around the circle, in clockwise direction with the #1 cylinder at the top. Engine orientation within cars The simplest situation is a longitudinal engine located at the front of the car, which means the engine's orientation is the same as the car's. This illustrates that the rear of the engine is the end that connects to the transmission, while the front end often has the drive belt