Andy is of course correct. And thinking about it, why would anyone want to use the 'inferior' RR barrels when SP's are available.

The internals of the NSR150 are reasonable robust so the RR cylinder will struggle to stress anything. Even the SP with a pipe is only making 30 odd ponies with no engine work.

We ran 40hp NSR150's back in '96 and didn't suffer any engine failures. A bit of clutch slip was the worst we had to deal with but that was cured with some stronger clutch springs.