Big-bang firing order

A big bang engine is an unconventional motorcycle engine designed so that most of the power strokes occur simultaneously or in close succession. This is achieved by changing the ignition timing; sometimes in combination with a change in crankpin angle. The goal is to change the power delivery characteristics of the engine or exhaust sound. A regular firing multi-cylinder engine fires at approximately even intervals, giving a smooth-running engine. Because of a big bang engine's power delivery imbalance, there exists more vibration and stress in the engine. This imbalance can overwhelm the rear tire, and generally makes a slide harder to catch. Until recently, this has limited their use to racing.



Parallel twins
straight-two

The classic British parallel twins (BSA, Triumph, Norton, AJS & Matchless) had a 360° crankshaft that, compared to a single, gave twice as many ignition pulses, which were evenly spaced.

The early Japanese parallel twins, like the 1966 Honda “Black Bomber” and Yamaha TX500, adopted a 180° crank that gave an uneven firing pattern. This configuration has the best possible primary mechanical engine balance for a parallel twin; the uneven firing was a by-product of this design.

The Yamaha TRX850 had a 270° crank that allowed a more regular firing pattern than a 180° crank, and less regular than a 360° crank. This configuration has the best possible secondary engine balance for a parallel twin; its exhaust sound and power delivery is identical to a 90° V-twin.

Twingles
For the Puch 250 twingle, see Split-single.

A twingle is a four stroke twin cylinder engine with an altered firing order designed to give power pulses similar to a single cylinder four stroke engine. It is well known that 4-stroke singles "hook up" better than 2-strokes in the dirt. This is because 4-strokes have half as many power strokes per crankshaft revolutions as a 2-stroke. This creates a recovery gap during which the rear tire regains traction.

Inline twins with a 360° crankpin offset and flat-twins can be easily converted into twingles by firing both of the cylinders at the same time. The Vintage Dirt Track Racing Association (VDTRA) 2010 Rules have banned vintage motorcycles from being setup as a twingle.

V-twin engine

A narrow angle v-twin such as the 45° Harley-Davidson naturally has slightly uneven spaced power strokes. By changing the ignition timing on one of the cylinders by 360° the power strokes are very closely spaced. This will cause uneven fuel distribution in an engine with a single carburettor. The Harley-Davidson XR-750 with twin carburettors was a popular bike to twingle. It had great success in flattrack racing. The sound of a v-twin twingle is generally disliked



Inline fours
I4 engine

A four-cylinder engine with a regular firing interval is sometimes referred to as a screamer. The regular delivery of power strokes can overwhelm the rear tire, and generally makes a slide harder to catch as well.[citation needed] A long bang fires both pairs of cylinders in quick succession; the power delivery is identical to a parallel twin with a 180° crank and similar to a v-twin. In 2005 Kawasaki experimented with this configuration on the ZX-RR MotoGP bike.

The 2009 Yamaha YZF-R1 has instead an uneven firing order.[5] The uneven power delivery is the same as a 90° V4 with a 180° crank, such as the Honda VFR800 and very similar to the Yamaha V-Max which has been lauded for its exhaust sound.[6]
4-stroke V4

2-stroke V4
The Honda NSR500 began and ended its life as a screamer. However in 1990 Honda connected both of the pistons in one bank to the same crankpin and both of the other pistons to a crankpin offset 180°. This NSR500 was called a 'big bang'. Yamaha created a big bang YZR500 in 1992. The YZR500 had 2 crankshafts like a U engine and the angle between each pair of cylinders was 90°, like a V4.

In 1997 Mick Doohan wanted to run a 180° screamer engine. HRC crew chief Jerry Burgess explains why: "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. The big bang has a lot of engine braking, so it upsets to bike into corners, then when you open the throttle you get this sudden pulse of power, which again upsets the suspension. Mick's secret is corner speed, so he needs the bike to be smooth and the 180 is much smoother