I found this on another forum a while back. It's been copied and pasted so many times now on different forums I think.
Typical gearbox code: W5M33-2-NQZK
Last 4 characters distinguish the gearboxes..
1st letter - Final drive ratio
N = 3.545 ratio
W = 3.909 ratio
2nd letter - gear ratios??
O = dunno ratio?
P = dunno ratio?
Q = close ratio?
R = wide ratio?
3rd letter - front diff
B = open front diff
F = ?
G = ?
W = viscous front LSD
X = ?
Y = open
Z = ?
M = Galant
K = HH/HJ Galant
E = CC Lancer
D = CB Lancer
Front LSD uses a different crownwheel, and a longer drivers side inner
W5M33-2-NRXD 1990 Cyborg hatch (4WD) 3.545 Ratio no LSD
W5M33-2-NRWE 92-95 Lancer GSR, Viscous Front LSD, 3.545 ratio.
W5M33-2-NRBE ????? Lancer GSR, 3.545 ratio no LSD
W5M33-2-NQBE 92 Lancer GSR 1.8rs no LSD 3.545
W5M33-2-NOBE Lancer GSR 3.545 no LSD
W5M33-2-WQYE, Lancer Evo 1 RS 3.909 ratio, no front lsd.
W5M33-2-WPGE, Lancer Evo 2 3.909 ratio, no front lsd.
W5M33-2-WPWE, Lancer Evo 2 3.909 ratio, viscous front lsd.
W5M33-2-UPYE, Lancer Evo 3 3.909 ratio, no front lsd.
W5M33-2-NQBK 91-2 Galant VR4 up to 4/92
W5M33-2-NQBM 92 Galant VR4 mfg 5/92
W5M33-2-WPVF Galant VR4 E84A
W5M33-2-WQNK Galant VR4 evo (3.909 ratio)
W5M33-2-WQFK Galant VR4 evo
W5M33-2-NPXV 91-94 Eclipse AWD 5spd mfg 6/90-2/94
W5M33-2-NNZT 95? Eclipse AWD 5spd mfg 3/94 [not sure about this one]
W5M33-2-NPZT 95-96 Eclipse AWD 5spd mfg 3/94-6/96
W5M33-2-WQWE 92-93 Lancer evo 1 RS (viscous front LSD) (3.909)
W5M33-2-WQFE evo 1 RS box
W5M33-2-WQGE evo 1 GSR box
wq -> is for the GVR4 RS and the evo1
evo2 and evo3 -> trannies each have letters that are different from all of the above and from one another.
The wq and evo2 and evo3 trannies DO NOT work with the US GVR4 3 bolt nor the US 1G 4 bolt rear diffs.