Yes I was planning on YZ250 heads, pistons and rods, carbs might be harder to achieve because of the angle the inlets end up at. I had thought bored out NSR250 carbs. Pipes will need to be designed as near to the right length and as big diameter as possible that will fit on the bike.
Ring life I'm not that worried about in itself - just would be good to know, it all add to the decision making process. The NS/RGV is currently road legal, but it's a track / weekend toy, rather than practical transport. The oil pump will probably have to go as well as the front cylinders will not have enough space to allow the oil pipes to come past. But I've learnt with the NS/RGV that whilst premix is a pain, having to take off a one piece seat unit to put oil in the tank is also a pain!
I figured it would be enough of a challenge to get the thing to work, I figured port timings, custom ignition etc and optimisation can happen later, as long as the thing is theoretically going to work and technically viable. And gets built correctly enough to work. I have adjustable advance CDIs for the NS, modded by BDK, but I've not played with the curves on them.
I have identified all the steps needed and have a method (and resource) to achieve each part, it's just weighing up the risk, the cost, the effort and probable end result.
I think vibration will be a problem and max RPMs will be quite limited. Porting will have to be set up to suit. But talking to the crank people it may be a case of run it and see what vibration you end up with, even at the very tight tolerances they work at.
The powervalve I'm hoping will really help, but making measurements on the frame and engine, I will have to either not have a powervalve on the rear cylinder, or have a very tight initial turn on the pipe.
No doubt I'll be round to yours at some point for some expert advice! The main thing I'm keen to avoid is a load of money spent and a non working / crap engine.
I guess the real reason for asking is - if someone says 'don't use a YZ barrel, there rubbish' or similar. I rode one years ago and it seemed bonkers fast, but then I'm not very good at riding off road bikes...
Cheers, Mat.