A big bang engine has an unconventional firing order designed so that some of the power strokes occur simultaneously or in close succession. This is achieved by changing the ignition timing, changing or re-timing the camshaft, and sometimes in combination with a change in crankpin angle. The goal is to change the power delivery characteristics of the engine. A regular firing multi-cylinder engine fires at approximately even intervals, giving a smooth-running engine. Because a big-bang engine has uneven power delivery, they tend to run rougher and generate more vibration than an even-firing engine.
An early big bang application and possibly the source of its discovery is reputed to be American west coast desert racing off-road and also flat track racing motorcycles in the 1960s where it was thought that large capacity single cylinder engined bikes had better traction compared to twin cylinder engined bikes with similar power, hence 360 degree crankshaft twins were reconfigured to fire both cylinders at the same time, giving the same power impulse interval as a single.
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