The various components of the engine are also vital to the performance of the vehicle. As certain components were mentioned previously, they will now be explained. The core of the engine is the cylinder. This is where the pistons slide up and down, and where all of the four strokes of an engine are performed. Vehicle engines are often classified by their number or arrangement of cylinders. The four-cylinder vehicles are the smallest. They are often aligned in a row (in-line four), but can also be aligned horizontally, two on each side, stroking away from each other. Many foreign cars use this technique, and refer to it as a "flat-four". The larger vehicle engines are constructed so that the pistons stroke in a V form, with three or four pistons on each side of the engine. This is why engines are referred to as either a V6 or a V8. The spark plug is the component that supplies the engine with ignition. The signal comes from the ignition box and must be timed perfectly for correct performance. The intake and exhaust valves are what allow fresh air and exhaust into and out of the cylinder. The valves are pushed into the cylinder my means of the camshaft, which is a cylindrical rod that had oblong lobes that push the valves as it spins. The pistons are cylindrical pieces of metal that move up and down inside the cylinder. The pistons must be of the highest quality of metal because they go through a large amount of friction, as well as the explosions. The combustion chamber is where compression and combustion take place. This is the area that is unoccupied by the cylinder when it is on its lower strokes. The connecting rod connects the piston to the crankshaft. It can rotate at both ends so that its angle changes as the piston moves and the crankshaft spins. The crankshaft turns the pistons" up and down motion into a circular rotation, just as the crank on a jack in the box does.