A big bang engine has an unconventional firing order designed so that some of the power strokes occur simultaneously or in close succession.
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 engine 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.
A 270° crank gives the best possible secondary engine balance for a parallel twin, and its exhaust note and power delivery resembles those of a 90° V-twin.
[citation needed] A narrow angle V-twin such as the 45° Harley-Davidson naturally has slightly unevenly spaced power strokes.
The "split" in this case is referring to the difference in phase between piston pairs in "opposite" banks that would normally share a crank pin in a four-stroke engine.
Just as with a boxer-four, piston pairs from opposite banks reach top-dead-centre at the same time, but with a crankpin split of only 60° instead of 180°, potentially giving a shorter and stronger or stiffer crankshaft.
A "long bang" inline 4 engine fires both pairs of cylinders in quick succession or simultaneously; the power delivery is identical to a parallel twin with a 180° crank and similar to a V-twin.
This is primarily because each piston needed its own sealed crankcase volume for the purposes of efficient induction, where in some cases separate crankshafts served each bank in order to achieve this.
HRC crew chief Jerry Burgess explained "The 180 got back a direct relationship between the throttle and the rear wheel, When the tire spun I could roll off without losing drive.