Honda NR500 oval piston. The Honda engineers said that the biggest challenge were the oval piston rings
Amazing Bike Tricks -
Honda NR750. Oval pistons, 32 Valves (8 per cylinder!), Gear driven cams, Dual spark plug heads, 20k RPMs. Carbon/ Graphite body work. Incredible motorcycle. Especially, given it's more than 20 years old !
alfonslx2: Honda 50 cm3 RC 115.16 chevaux - 21 000 tr/mn More info: http://velobanjogent.blogspot.pt/2008/06/honda-50cc-racersrc112rc113-rc114-rc115.html Source: Jan Thiel