I have wondered about this for awhile....It seems that my old valver engine with the JB3 gearbox had a totally different ratio in 4th gear to the JC5? 4th gear seems shorter in my JC5 box than the JB3 box did and seems to work alot better aswell. It will give around 107mph on the willy limiter on JC5 box 6,500rpm. I can't actually be sure if 3rd gear was also a shorter gear in the JB3 aswell? I can remember the revs dropped much more through a 3rd to 4th gearbox on my valver setup though. Has anyone notcied this? Sorry about the dragged out information lol