look very closely along one of the grooves the shift fork's peg slides in (cant remember which one he does) and at a certain spot you can see where an end mill has just widened the slot at that point by maybe .100" so the gear can slide over a little more and the dogs make full engagement (you'll see swirly machine marks just barely)
i think the drum mod is a blueprinting type thing so a certain sliding gear can make it all the way over and not bend the shift fork like a backcut tranny could do if the angles on the dogs really pulled hard under load and the fork is limited in moving sideways by the width of the slot cut at that point
nitrous cut is rounding the backside of the dogs so if the bike spins the tire (trans speeds up from inertia, overruns the rear wheel speed, and pegs the downshift side of the next dog)....instead it will "ratchet" so to say (instead of sticking to the factory slight backcut or even straightcut on the next dog)...then it can disengage even under load and go to the next gear
the way robinson and fbg do it, if requested, is mill off every other dog on the high gear set (slider gear on input shaft and its adjacent engaging gear on both side) so as to open a larger "window of engagement" for the higher gear changes contolled by that single fork on the input shaft
its hard to understand unless you really know how these constant mesh motorcycle tranys work and exactly what backcutting is and what i mean by pegging the downshift side (with no chain and a bike in gear think of the little bit of rotation you can get from the countershaft sprocket back and forth....)
look at robinsons website at what auto gear look like too and it will help understand it (ramps)
theres some tricky stuff that can be done to these trannys....read prostars rule book about illegal trannys.....windowed drums, split gears, overdriving, spring loading the gears
