Supermono, the engineers' class with few rules, has spawned many a monster single. Mine is an adapted Godden 500, kitted with three reed valves, a transfer pipe, injector throttle body and 12 years' track development - resulting in a full flow system aided by the normally detrimental crankcase pressure.
Each upward piston stroke 'sucks' a volume of air via two reed valves into the crankcase.
Each downward stroke displaces a large fraction of these volumes via an outlet reed into a long transfer pipe (around the saddle).
As the head inlet valves open, this transfer pipe volume gushes into the cylinder resulting in good volumetric efficiency, brutal bottom end torque and better acceleration. The more it revs, the more HP gain over a standard engine. This one revs to 10,000 rpm.
I'm building my own 1300cc Ellwood Hybrid single now, with four reed valves, and shall race it in the British Supermono series.
If there's any budding sponsors who want to see (and hear) the 500 version racing at the 100 years jubilee TT , then get in touch.