THE FIVE-VALVE HEAD

Why Yamaha’s en­gine rev­o­lu­tion was about far more than pub brag­ging rights

Motorcycle News (UK) - - Garage -

Ray Stringer

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.

Newspapers in English

Newspapers from UK

© PressReader. All rights reserved.