OVAL PISTONS

In 1991 I remember reading about a Honda road/race bike with a 750cc 4 stroke V4 with oval shapped pistons and 8 (eight!) valves per cylinder. It was like a scaled down V8. What ever happend to that? Imagine a 1.5 V8 like that!!

The model was a NR750 and you could buy one from your Honda dealer for about $100000+AUD it was meant to be a attempt to get a four stroke back into GP racing but didn't work quite as well as Honda hoped.
check it out at http://www.california-designs.com/nr750.htm

I have a Popular Mechanics issue somewhere with an in depth analysis of Honda's NSR500 as well. It proved a little too fragile and prone to excess blowby. It too sported 4 intake and 4 exhaust valves per cylinder and reportedly revved over 18,000 rpm.

Apparently, one of the biggest problems with the oval pistons was the difficulty in sealing them. The piston rings didn't like the transition from curves at the end to straight and tended to develop a wave-like ripple.

Oval pistons were specifically banned by F1 at about the same time. No one had tried them, but Honda were dominant at the time and it was believed that to allow them utilise yet another trick would escalate the costs further.