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Big-bang firing order
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Big-bang firing order
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, it tends to run rougher and generates 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 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.
In a parallel twin, both pistons reach top dead center at the same time. In a parallel twin where the pistons move up and down at the same time, the crankshaft angle is 360 degrees.
The classic British parallel-twins (BSA, Triumph, Norton, AJS & Matchless) all had 360° crankshafts that, compared to a single, gave twice as many power/torque impulses for a given amount of crankshaft rotation, these impulses are equally spaced to give an equal firing interval: once every 360 degrees of crankshaft rotation. However, the 360 twin had a mechanical primary engine balance that was no better than a single.
Inline twins, Japanese inline 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, but gave an unequal firing interval; 180 degrees, 540 degrees, 180 degrees, 540 degrees etc - due to one of the two pistons needing to be at top dead centre at the beginning of the power stroke.
The Yamaha TRX850 pioneered the use 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.
The BMW F 450 GS uses a 135° crank, which results in an uneven firing interval (225 degrees, then 495 degrees, and that in a repeating pattern). The same firing order was also in use during the 1980s and 1990s for two V-Twin engines: Two Honda models, the touring bike PC800 Pacific Coast and the enduro bike XLV750R, used 45° V2 engines with a split pinned crankshaft using a crankpin offset of 90°.
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.
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Big-bang firing order
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, it tends to run rougher and generates 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 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.
In a parallel twin, both pistons reach top dead center at the same time. In a parallel twin where the pistons move up and down at the same time, the crankshaft angle is 360 degrees.
The classic British parallel-twins (BSA, Triumph, Norton, AJS & Matchless) all had 360° crankshafts that, compared to a single, gave twice as many power/torque impulses for a given amount of crankshaft rotation, these impulses are equally spaced to give an equal firing interval: once every 360 degrees of crankshaft rotation. However, the 360 twin had a mechanical primary engine balance that was no better than a single.
Inline twins, Japanese inline 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, but gave an unequal firing interval; 180 degrees, 540 degrees, 180 degrees, 540 degrees etc - due to one of the two pistons needing to be at top dead centre at the beginning of the power stroke.
The Yamaha TRX850 pioneered the use 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.
The BMW F 450 GS uses a 135° crank, which results in an uneven firing interval (225 degrees, then 495 degrees, and that in a repeating pattern). The same firing order was also in use during the 1980s and 1990s for two V-Twin engines: Two Honda models, the touring bike PC800 Pacific Coast and the enduro bike XLV750R, used 45° V2 engines with a split pinned crankshaft using a crankpin offset of 90°.
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.