The Clatworthy bikes are amazing machines.
If you buy a modern bike, you usually get that. But some people still tune them. To me, that is what is wrong with modern bikes. If you make them go faster, they become far too fast. If you tune and old Commando. they become fast enough to be fun without creating a disaster.
When I bought my 6 speed TTI box, I could have had magnesium instead of aluminium cases. My bike would probably have become 20 MPH faster in my imagination.
Four speeds close ratio is all you need to make a Commando fast, but first gear is usually too high for a clutchn start. 3 speeds close and high with a normal commando first gear was probably all I needed, but I got the hump. What I race against have been developed into 4 cylinder superbikes. I got frustrated - the bit I lost at the start of two races was impossible to regain. The one time I got brave and revved the tits off the motor on the start line, I got past them at turn 2 and ended up 100 metres ahead of the three leaders. The clip for the fuel line is right up under the tank where it cannot be seen. Both my helper and I both forgot it. The lower two speed in the 6 speed box are used to launch the bike away from the start. One low gear and four high and close is enough. The gap between first and second is irrelevant, once you are moving. You never go back to first during a race.
Of course it would !
I would never increase capacity to get more go. My motor is 2mm oversize, so it is probably almost 900cc. I think that if it was a 750, I could probably make it go faster. Jim's long rods and light pistons look very good to me. With a 920cc engine, you probably get more torque which would make the bike a better ride on public roads. But if it came to a speed contest, there are different effects when you have light engine internals.
What about if you have both, have you ever thought about that?
There is another old saying 'torque wins races'. The gear box is a torque multiplier. On a short tight circuit, torque is more beneficial than on a big circuit with wide sweeping bends. My 500cc short stroke Triumph was far quicker than my Seeley 850 around the tight bits of Winton, if I lowered the overall gearing - but too slow at the ends of the straights. I usually ran higher gearing so I did not end up running into the back of guys at the ends of the straights. The Seeley 850 is much faster in sum total and much safer. One of my mates said 'if you have a torquey motor, you do not need a close ratio gearbox'. I tried racing with the normal Commando gearbox ratios - the bike was too slow everywhere.
