the picture actually lies, not as wide as it looked
I did the old 60% of the bore width and used the dunno what its called shape - loaf of bread? so that most of the ex port area was above the transfers
the sides were divergent easing the rings gently out and back in
vertical sides as you know just allow it to plop out and in = snagsville.
and oval ex ports most of the area blow transfer opening calls for a good bit of pipe assist
then I just went wider and wider until I hit 70% with no problems
I was just playing. I tried flat roofed transfers = no difference then to get them angled again I had to raise them and matched the exhaust height so it revved too high for the big heavy old crank
it was just fun -learning by mistakes
same road different/(better) pipe and porting only revved to 8-9 ish (analogue tacho no worky)
in the end I got it going 120mph and 100 sat upright and could play and embarrass the litre hypersports guys on the right road thanks to an enthusiastic riding style that belies my old codgerism
aplologies for bragging
i am in awe of you guys and your achievements with so little to work with and i am now inspired to have a go
just need one more beer......