Big-bang firing order is an unconventional firing order used in motorcycle engines.

A single-cylinder four-stroke engine has a firing regime of 0-0-1-0. The classic British parallel-twins (BSA, Triumph, Norton, AJS & Matchless) had 360-degree cranks that, compared to a single, gave twice as many ignition pulses, which were well spaced (1-0-1-0), but the dynamic balance was no better. They vibrated just like singles. The early Japanese parallel twins, like the 1966 Honda “Black Bomber” and Yamaha TX500, adopted a 180-degree crank that gave an uneven firing pattern of 1-1-0-0; but the much-better primary balance allowed high rpm (and thus more power) without the engines shaking themselves to bits. However, the 180-degree engines could feel "buzzy" or "tingly", through secondary out-of-balance forces derived from a rocking couple.

The Yamaha TRX850 had a crank that allowed a more regular firing pattern than a 180-crank, and less vibration than a 360-crank. Just like a 90-degree V-twin (but unlike the 180 & 360-cranks) the 270-crank never has both pistons stationary, and this gives a dynamic benefit. Also, although its firing interval is not as uneven as the 180-crank or 90-degree Vee (which both fire 1-1-0-0) the 270-crank avoids being perfectly even. This feature is said to allow better power delivery to the rear tyre, giving two fairly close power pulses followed by a "recovery gap".

Current performance 4 stroke engines utilize the big bang firing order to create a recovery gap during which the rear tire regains traction. A regular interval 4 cylinder engine fires every 180 degrees which can overwhelm the rear tire, and generally makes a slide harder to catch as well. A standard big bang firing order places 2 cylinders firing simultaneously, similarly to a v-twin. The 2009 Yamaha R1 has instead an uneven bang firing order, where the crankshaft will fire thrice with 90 degrees of separation between the firings, will fire again after 270 degrees, and will start the process again after an additional 270 degrees rotation. The uneven bang is the same as a V4, where the VFR and 2009 R1 share the same firing orders.

[edit] Applications

Big-bang firing order was used in MotoGP racing.^[1] The 1992 Honda NSR500 may have been the first racebike to use this scheme.

The big bang concept was adopted for the 2009 Yamaha R1 engine, which has a 4-cylinder crossplane crank.^[2] The 2009 Triumph Thunderbird 1600, which has a 1600 cc parallel-twin engine, has adopted a 270-degree crank to obtain such special benefits.

[edit] References