The NSR150SP is actually an evolution of the NSR150RR, which was an evolution of the NSR125.

It basically started it's life as the 125 and then Thai Honda (well Japan) redesigned the engine to 150cc for the Thai market, and built a frame around this. It was originally manufactured (the engine) in Italy, and the frame parts came from Japan. It was assembled in Thailand.

The cylinder is nikasil plated, so boring out necessitates replating and finding a suitable piston.

40hp is possible, but you'd be looking at some major engine work and it's streetable factor will drop to zero!

If it's got a pipe and carb then you'll be lookijng at around 30hp. Maybe. Getting more requires careful engine work.

As for top speed. A shade over 100mph probably. Ignore the wildly optimistic speedo as it'll probably show about 195kmh, which is tosh. We had a 40hp NSR150SP on the brake that was set up for Shah Alam in Malaysia. Peak rpm in 6th gear showed 110+mph. And this was the fastest NSR150SP in Asia, running HRC parts and burning avgas.

As it is, is should beat most 125's, but may have a bit of trouble against a well set up, fully derestricted Aprilia RS125.

If you want to be a loon, then any cc will do. I've hadgreat fun hooning around on an old AR80 before, but if I need an adrenaline buzz then I'll jump on the 300.