Big-bang firing order
||This article or section appears to contradict itself about whether it is a conventional or a "big bang" engine that can "overwhelm the rear tire". (October 2011)|
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, 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 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, but when the rear tire does slide, the temporary lull in power between power strokes generally makes the slide easier to catch.
Twins and twingles
BSA, Triumph, Norton, AJS, Matchless and BMW F800S
BMW R series
|Parallel twin||180°||180-540||1-0-1-0-0-0-0-0-||1966 Honda “Black Bomber”, Yamaha TX500 and Kawasaki ER-6|
90° V twin
Triumph Thunderbird (since 2009)
|45° V twin||360°||315-405||1-0-0-010-0-0-0-||Harley-Davidson|
|45° V twingle||360°||45-675||110-0-0-0-0-0-0-||Modified Harley-Davidson XR-750 for flat track racing|
The classic British parallel-twins (BSA, Triumph, Norton, AJS & Matchless) all had 360° crankshafts that, compared to a single, gave twice as many ignition pulses which were evenly spaced. However, the 360 twin had a mechanical primary engine balance that was no better than a single.
By contrast, Japanese parallel twins of the 1960s (such as the 1966 Honda “Black Bomber” and the Yamaha TX500) adopted a 180° crank that afforded perfect mechanical primary engine balance. However, the 180° crank yielded some "tingling" secondary vibration (which could be minimised with a balance shaft), and an uneven firing order.
The Yamaha TRX850 pioneered the used of a 270° crank. This configuration allowed a firing pattern more regular than a 180° crank, and less regular than a 360° crank. 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.
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 four-stroke singles "hook up" (or get and maintain traction) better than two-strokes in the dirt. This is because four-stroke singles have half as many power strokes per crankshaft revolutions as a two-stroke single. This creates a recovery gap during which the rear tire regains traction.
Inline twins with a 360° crankpin offset or flat-twins can be easily converted into twingles by firing both of the cylinders at the same time and installing a camshaft or camshafts that operate both cylinders' valves in parallel. Because many such engines already employ the wasted spark principle, only the camshaft modification is necessary.The Vintage Dirt Track Racing Association (VDTRA) 2010 Rules have banned vintage motorcycles from being set up as a twingle.
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.
|I4 'Long bang'||180°||180-540||2-0-2-0-0-0-0-0-||Shinya Nakano's Kawasaki Ninja ZX-RR|
|I4 'Uneven bang'||crossplane||180-90-180-270||1-0-1-1-0-1-0-0-||2009 Yamaha YZF-R1|
|1-0-1-1-0-1-0-0-||1985-2007 Yamaha V-Max
|90° V4 'Twin pulse'
||70°||90-200-90-340||1-1-0-1-1-0-0-0-||Ducati Desmosedici RR|
|90° V4 'Droner'||360°||90-270-90-270||1-1-0-0-1-1-0-0-||Honda VF/RC30/RC45|
|112° V4 'Big bang' (2-stroke)||180°||68-292-68-292||2-2-0-0-2-2-0-0-||1990 Honda NSR500|
|90° V4 'Screamer' (2-stroke)||180°||90-90-90-90-90-90-90-90||1-1-1-1-1-1-1-1-||1984 Honda NSR500|
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. 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 was the first production sportbike to use a crossplane crankshaft and big-bang firing order. The 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.
|This section requires expansion. (April 2010)|
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 two 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 the 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."
- Kawasaki continues big bang testing, MotoGP.com, 20 March 2005, retrieved 2010-04-20
- 2008 Ducati Desmosedici MotoGP Replica, Fast Dates, 2008, retrieved 2010-04-20
- Honda NSR500 GP Racing History, Ultimate MotorCycling, 2010, archived from the original on 10 May 2010, retrieved 2010-04-20
- NSR500, Superbike Planet, retrieved 2010-04-20
- 2009 Yamaha YZF-R1 Features Uneven Firing Order For Improved Power Delivery, Yamaha press release via Road Racing World, 2008, retrieved 2009-05-23
- 2009 Star V-Max Review/Test, Motorcycle.com, August 26, 2008, archived from the original on 1 May 2010, retrieved 2010-04-20