THE FIVE-VALVE HEAD
Why Yamaha’s engine revolution was about far more than pub bragging rights
Successful club and national racer in the 80s and 90s who turned to tuning in 1992. He now builds the Bennetts Suzuki engines and acts as Crew Chief for Sylvian Guintoli.
The Yamaha FZ750 was the first bike to have a five-valve head when it was launched in 1984. It was a big deal for Yamaha as it was its first supersport bike so the budget for engine development was substantial, giving the bike inclined cylinders, downdraught carbs and those 20 valves.
The five-valve head became part of Yamaha’s highperformance brand, used in their V8, V10 and V12 Formula One engines, as well as the YZ250F and YZ450F motocross bikes, so they continued to be developed and were used in the Fzr-series bikes with the EXUP valve and then the R1.
By 2004 Yamaha had reached the limits of the concept and went back to a fourvalve head on the R1 and other engines. By then metallurgy had improved to such an extent that the large valves in the R1 were lighter than their smaller five-valve predecessors. Going back to four valves allowed a shallower valve angle so the combustion chamber dome height could be reduced to raise compression.