I am putting together a trans for my CRX road racer. I am finding it difficult to source any good condition 5 speed trans, but I know of a good 4 speed from a CX. Since I never use 5th gear anyways I was wondering if the 4 speed could work if I just swapped in the Si 2-4 gears. Probably use a 4.9FD and MFactory LSD also. Has anyone tried this? What parts do I need, what do I need to watch for to make this work? Constructive advice appreciated, thanks!

 

I don't see why the gear swap wouldn't work but there might be a bearing size difference on the differential that'll prevent the LSD unit from being installed. I have a 4.9FD on my car with the CX transmission and I had to grind the case a little bit to clear the ring gear.

 

Thanks! Glad to know it works.

Now you have me thinking of close ratio ZC gears too, lol. Need to do some gear calcs and review my data to see if that would help on the track. I wish my 3 & 4 were about 500-ish rpm closer.

 

Just had another thought... would there be less power loss through the transmission if there is one less gear (no 5th)?

 

As in drivetrain loss? I wouldn't think so, each gear is essentially allowed to rotate freely until it's engaged. I guess for the super **** engineer that likes to crunch numbers there's going to be some loss per gear but I'd imagine it to be negligible to the typical enthusiast. There's a a couple of transmission experts on here, hopefully they chime in. I haven't been on here regularly for the last couple of years so I don't know how active transzex/Mista Bone or Aquafina are.