Dual fire ignition systems fire both spark plugs from a single coil at the same time. The majority of the spark energy goes to the cylinder under compression while a small portion goes to the cylinder on the exhaust stroke causing a small wasted spark. Single fire ignitions separate the firing pulses, only firing the cylinder under compression. The main advantage of dual fire systems is simplicity and low cost. The advantage of single fire systems are smoother engine operation and the elimination of the popping that sometimes occurs when long duration camshafts are used. There is no horsepower advantage with single fire ignition systems.