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There is plenty of technical language used to describe the engines which power the racing prototypes on which the riders participate in the MotoGP™ World Championship, but most of it is fairly easy to understand if taken piece by piece and explained simply, even if the machinery itself is technologically advanced and complex in nature.
2-stroke and 4-stroke - 2-stroke engines were predominant in the World Championship until the switch to the 990cc 4-stroke class in 2002, reflecting production trends, with 2-stroke bikes being the popular choice from the 1960s through to the 1990s.
If 2-stroke engines proved more powerful than 4-strokes with similar engine capacities and similar rev counts, 4-strokes engines are more energy efficient and greener. This is because 4-strokes have a dedicated lubrication system, while 2-stroke engines burn a mixture of oil and gas.
As most manufacturers shifted their production towards bigger 4-stroke powered machines, the move to a 4-stroke prototype formula only seemed natural.
The key difference between the two types of engine lies in the combustion process: the four ‘strokes’ refer to the intake, compression, combustion and exhaust movements which occur during two crankshaft rotations per working cycle.
The 2-stroke internal combustion engine differs from the 4-stroke engine in that it completes the same four processes in only two strokes of the piston.
Single cylinder, two cylinder, four cylinder and six cylinder engines - While technical rules restrict the Moto3™ World Championship to single cylinder engines and Moto2™ to the Official Engine, MotoGP™ bikes were allowed from one to six cylinders or more up until 2012 when a limit of 4 cylinders with a maximum cylinder bore measurement of 81 mm was introduced.
According to the FIM rulebook, the number of cylinders dictates what the minimum accepted weight of the bike will be, and ballast may be added to achieve it. Due to unit cylinder performance and power-to-weight ratio, all the MotoGP™ manufacturers opted to use four cylinder engines even before the regulation was introduced.
However, those engines come in different forms, as some manufacturers, such as Ducati, Aprilia and Honda currently opt for V4 architecture, while Yamaha, BMW and Kawasaki have developed ‘inline four’ engines.
With V4’s the cylinders and pistons are aligned separately to each other, so that they take on a ‘V-shape’ from an angle looking along the crankshaft axis. This configuration decreases the total height, length and weight of the engine, in comparison with straight engine inline equivalents.
The choice of engine architecture has as much to do with design philosophy and the manufacturer’s heritage as with weight transfer and goals in terms of bike ‘rideability’.
Meanwhile, the terms 250cc(Moto3™), 600cc (Moto2™), 1000cc (MotoGP™) used to describe the three current categories in the World Championship simply refer to the ‘engine displacement’ or ‘cubic capacity’ of the respective machinery.
DEVELOPMENT THROUGH THE AGES
The biggest change in the premier class over the years has been the switch from 4-stroke to 2-stroke engines and back to 4-stroke in 2002, reflecting the need for technical progression and innovation in the sport - in keeping with the development of production bikes.
In the early days of the World Championship the premier class was dominated by 4-stroke machinery from mostly European manufacturers. The early 4-stroke engines were cumbersome, heavy, required a lot of maintenance and were never the most reliable of units.
Through the 1960s Japanese manufacturers such as Suzuki and Yamaha started to make their presence felt in the smaller cylinder classes with 2-stroke machinery. The lighter 2-stroke presented more possibilities for tuning and was seen as the future of the sport.
Although the 1970s and even 1980s saw a period of technical change that permitted even private ‘built in the garage’ motorcycles to go Grand Prix racing, it was the might of the Japanese engineering and initiative that would soon provide the most competitive racing tools.
THE EMERGENCE OF 2-STROKE
As the Japanese slowly forged ahead with 2-stroke technology, the 4-strokes would fade out in a matter of seasons as the 500cc four-cylinder 2-stroke became available on a production scale from Japan.
With the 2-strokes becoming more reliable and more powerful, the engines actually threw more emphasis onto the rest of the motorcycle and evolution began at a rapid rate through the 1980s. Tyres, suspension, aerodynamics and even chassis design all saw a wealth of development.
In the early 1990s, speeds had reached a peak in MotoGP. Light, agile, and extremely hard to ride, the 500cc bikes were faster than ever to ride as an all-Japanese premier class sought to push the performances of the machines to the limit and new heights. By 1992 a breakthrough emerged when Honda started to experiment with a revised firing order on their all-conquering NS500.
BIG BANG & THE SCREAMER
Dubbed ‘Big Bang’, the revised crankshaft mechanism placed an emphasis more on acceleration than outright top speed and Mick Doohan went on to dominate the class on the new bike. Honda also produced a V-twin version of their four cylinder motorcycle which helped privateers remain competitive against the factory bikes and for the first time technical emphasis leaned more towards corner speed than outright horse-power; a trait that remains to a certain degree in MotoGP™ today.
By the late 1990s Doohan had reverted back to the ‘harsher’ engine order in his quest for more speed. Nicknamed the ‘Screamer’, this and the ‘Big Bang’ version of the NS500 won World Championships from 1994 to 1999.
In 2000 Suzuki enjoyed a last hoorah on the RGV 500 2-stroke; a motorcycle developed from predecessors that had originally dominated the class back in the late 1970s and early 80s.
With 2-stroke technology reaching a plateau, improved 4-stroke engines marked the way forward. The MotoGP™ landscape changed in 2002 in order to ensure that there was continual technological evolution, and 990cc 4-strokes were allowed to compete with the 500cc 2-strokes. The 4-strokes were immediately competitive, and by 2003 no 2-strokes remained on the grid. The following six seasons produced a massive acceleration in the technical possibilities with variable cylinder structures and quantities, telemetry, data collection and manually adjustable engine mapping switches now standard.
MotoGP is now a highly evolved and scientific competition with traction control and electronics playing an important role in the delivery of the power and adjusting the balance of the motorcycle to make the best use of the engine’s performance.
The MotoGP™ category saw the engine size reduced from 990cc to 800cc in 2007, with an aim to reduce speed. While the speeds remained the same, they did so through the size and dynamics of the motors placing more focus on the corner speed of the machinery, as opposed to the brute power of the 990s.
In line with cost reduction policies, engine restrictions have been enforced since 2009. A regulation stating that each rider is allowed only 6 engines at their disposal for the whole season commenced in 2010. Limiting the number of engines means the manufacturers have to produce more reliable powerplants, which calls for reducing their power output and revs, hence slowing down the overall increase in performance of the bikes.
A move to a 1000cc formula in 2012 was accompanied with further restrictions than were in place during the 990cc era. The number of cylinders is limited to 4 and the maximum cylinder bore (the diameter of the cylinder) is 81mm for bikes with a minimum weight of 153kg (or 150 kg for an 800cc engine).
The former 125 and 250cc classes were hosts to 2-stroke engines, being the original homes of the 2-stoke. Firms such as Derbi, Kreidler and Bultaco were 50cc, 80cc and 125cc competitors with 2-strokes in the 1960s, and 2-strokes littered the 350cc division.
Outside the premier class, 2-strokes permitted the most cost-effective means of racing and being competitive. The 2-stroke prospered with carburetion, tuning and set-up becoming a specialised skill that saw a host of names in the Grand Prix paddock making their names through the late 1970s, 80s and into the 90s.
Today, the general consensus is that the limits of 2-stroke technology have largely been reached in all classes, and therefore 2012 was the dawn of a technically relevant new era, with four stroke motorcycles filling all three fields of the championship.
The Moto2™ class replaced the 250cc category from the start of 2010. The bikes are powered by a 600c 4-stroke spec Honda engine that produces around 140bhp, with a prototype chassis free from limitations of design and construction.
The 125cc category was replaced with Moto3™ from 2012. These are single cylinder, four-stroke engines produced by any manufacturer, with a crankshaft speed limit of 14,000rpm and a spec ECU.