"As previous mentioned, the strongest feature of the YZR-M1 is its short wheel base combined with a long swing arm. The in-line engine configuration suits this concept best," he said. "Also, the distance between the crankshaft and axle drive has been shorted year by year and this has enabled the use of a longer rear arm."
"Looking back to 2002 and 2003, the comments from the 2003 press test on the YZR-M1 said everything. The engine was so aggressive and difficult to control," he admitted. "Everybody that rode the bike said that '2004 will be a very difficult season for Valentino'.
"But at the same time, we had already started to develop the new four valve and un-even firing engine. This engine was tested around 2003 Christmas time and we had a big present from Santa Claus!
"When we started working with Valentino at Sepang in January, he confirmed this was the best direction for the engine. But we struggled to get more power from this engine. However, year by year, we improved the power and revs. The engine was given a shorter stroke to increase the revs even further, and for this we changed the valve train system from chain to gear driven."
The results of these changes can be seen in the 'Evolution of engine performance' diagram (lower picture) which illustrates how maximum engine power ands revs has improved year on year - despite fuel tank capacity reductions.
"This diagram shows how engine performance has improved. From 2002-2004, the power has gone up steadily. After the 22 litre fuel limit regulation was introduced [for 2005] the improvement in power slowed down a little. On the other hand, the gear train system gave the engine more revs. Between 2002 and 2006, the engine power rose by approximately 35 horsepower and revs have increased by approximately 3000 rev/min," he confirmed.
The third and final 'theme' of the M1's development since 2002 has been the evolution of the engine management system (lower picture, 'Evolution of EMS'). This initially began as a way of controlling the effect of engine braking when a rider shut the throttle, but has since grown into a much more complex control system covering torque control, traction control, wheelie control, launch control and more.
"When the [four-stroke] MotoGP class started in 2002, EMS just meant engine brake control. Every team struggled with the engine braking generated by the new four-stroke engines," said Tsuji. "The YZR-M1 had the problem too so we tried several systems and the engine braking problem greatly stimulated the development of EMS.
"Through these developments, the YZR-M1 has changed from an ICS [Idle Control System)] to fly-by-wire system."
Fly-by-wire is a term borrowed from the aviation industry and means a control system which works without having a direct mechanical link; for example there is no cable between the throttle and engine. Instead such systems operate indirectly - the rider input acts as a 'request' which is sent electronically to the management system, this then checks data from other sensors (wheel speeds, gear, lean angle etc) to determine how best to execute that 'request'.
"Now the throttle not only controls the engine power but also the chassis!" revealed Tsuji.