The same in-line-4 engine format as the 990cc M1 was chosen as the best format to achieve the YZR-M1 chassis development goal of a short wheelbase and a long swing arm. Also an uneven firing interval of 90 degrees, 270 degrees was adopted. Compared to a 180-degree firing interval, the 90/270 interval has the advantage of making it possible to reduce fluctuations in inertial torque.
The regulation changes in displacement and fuel supply limitation resulted in an engine that was 8 mm slimmer, 18 mm lower in height, 5mm more compact in terms of the distance between the shaft axes and 3.5 kg lighter in overall weight. At the same time, the reduced displacement led to a decrease of about 3 to 5% in top speed and over the course of the season seven upgraded versions of the engine spec were introduced with the aim of increasing the power output. We used Version 2 of the basic spec for the season opener in Qatar and round two at Jerez, and at round three in Turkey we used Version 3 with improved power output and higher rpm. Version 3 continued to evolve up to Version 3.6 by round 11 at Laguna Seca in the US. Then Version 4 with improved output and fuel economy was introduced at round 12, the Czech GP. This version continued to evolve up to Version 4.3 by the last round of the season at Valencia. The total result for the season was a 4% increase in power output, a 1,000 rpm increase in top revving and a 3% improvement in fuel economy. In the process we were able to reduce the gap with the fastest top speed recorded at each circuit by the competitors to about 1%.
Brno
