can anyone think of any reason that you couldnt put a 400rrsp close ratio box into an fzr600 motor as i have started to put together hybrid no 2 while i wait for some bits to arrive for the other one and started thinking if it could be done or if it may have already been done.the motors are so similar i wondered if it could be done as the sp gearbox ratios are perfect for the track,and it would be exellent to have the 600s power with the sweet sp box.the other hybrid 400sp/fzr600r has reached a bit of a tempory halt as i think my 600 ecu has gone awol.im waiting for another to arrive so i can ride the bloody thing!so come on can it be done?

The theory is sound enough.
As long as the lower revving 600 motor is going to be suited to the gearbox but I gues you can vary that using the sproket ratios.

The FZR600R Foxeye does not have a much lower redline. It is at 13k revs rather than the 400s 14k revs.

Not sure what the redline is on the thundercat.

Alex.