On my quest to build a bike as close as possible to what HRC put on the grid in the SS/SP races ive come to the transmission and have been comparing the parts fiche between the standard and HRC transmission where obviously there are some differences yet some gears remain the same but still have differnent part numbers. Below is the HRC kit transmission set,

Main shaft 16T
Gear, C-1 41T
Gear, C-2 38T
Gear, M-3, M-4 20/22T
Gear, C-3 36T
Gear, C-4 35T
Gear, M-5 23T
Gear, C-5 33T
Gear, M-6 24T
Gear, C-6 32T

And the corosponding parts in the stock trans,

Main shaft, No. of teeth not listed in parts manual although i'll count the teeth next time im in the garage
41T
39T
20/22T
36T
35T
23T
33T
22T
29T

Firstly does anyone know why the gears that have the same anount of teeth in both the stock and HRC trans have different part numbers? and also for the gears that are different is it possible to swap in gears from another model? ie NC23 and NC29 assuming they have the gears with the right amount of teeth. looking at the parts fiches on CMSNL.com for the CBR's the transmissions all seem to have the same layout as the VFR but they dont list the amount of teeth for each gear.

I dont know the answer as I have never seen the HRC parts but there are some options.

The first is the great Honda maketing machine can charge more for a HRC part number

The second, and I would think more likely answer, is that they used different pressure angles and correction factors on the tooth design. For a road bike the most importaint things are noise and both gears must wear out at the same rate. For race transmissions bending strength is the most importaint, so the tooth shape tends to be shorter and wider at the bottom, rather than tall and thin.

That would make sense