Canadian John Williams won the world hillclimbing championship five times between 1972 and 1981. His first win in 1972 was on a pushrod harley running 75% nitro.
John decided to try something new, using a CB750 engine from a wreck. A custom frame with an extended swingarm made for better traction on near-vertical hills. John also decided 100% nitro was the way to go.
Nitro is an effective fuel because it contains a lot of the oxygen needed to burn, you can burn about 9 times as much nitro fuel as gasoline in a cylinder without being "rich". Nitro only has about 1/4 the actual energy output of gasoline though... but you still get close to three times the horsepower from a motor using it at 100%.
100% nitro proved too dangerous for even John though: Nitromethane is a high explosive but rather difficult to detonate and this property is not used in an engine - but if a tank of fuel detonated the rider would be blown apart. A railroad carload accidentally detonated in Illinois in the '50s killing two railwaymen and leaving a 30 meter crater 10 meters deep. To temper this high explosive danger he went with about 97% nitro with other the other 3% chemicals to eliminate the explosion hazard.
This got him about 250HP.
And a lot of championship wins. He actually had a racing team with three bikes, his two sons were the other two riders.
They developed the super long wheelbase frames still used in hillclimbing, although I'm not sure there is an actual championship any more.
The biggest risk with 97% nitro is that blow-by accumulates in the crankcase until an explosive mixture forms, then the engine is a bit unpredictable. The races he didn't win usually had scattered shards of his crankcase scattered over the hillside.
He abandoned the 750 SOHC4 in the last years of his career, using the relatively rare Benelli 750 "Sei" six cylinder engine as the smaller pistons allowed a higher rev limit. This is pretty much a stretched CB550 engine. On 97% nitro it was supposedly making well over 300hp at 13000 rpm. Quite a sound.
I have spoken to John several times, he's quite a storyteller.
