Hi there guys, my first post here. I too am looking for a very strong 4WD system for a possible 4WD street rod project, and may be able to help with some suggestions.
The GTR gearbox is incredibly strong, in Japan 1000+Hp drag cars are running in the eights on slicks with standard geaboxes, so strength is not an issue. The ratios are quite good too, 3.21, 1.90, 1.30, 1.00, 0.75 and gearboxes are fairly readily available. But the transfer case has a perculiarity in that it works in a rather unusual way. Expect to pay about $2000 for a complete gearbox and transfer case. The Last GTR (R34) used the Getrag six speed, not the old Nissan 5 speed used in all previous GTRs, and is well known to not be as strong, and prone to breakage on the drag strip as the older box.
The GTRs gearbox output shaft goes solidly to the rear diff as in any RWD car, and a wet multiplate clutch feeds power to the front wheels, on demand, activated by hydraulic pressure. There is no central diff, and it is not a full time 4WD system. It threfore needs some sort of electronic control system to make it work. Without that it will never work properly and may not do quite what you want anyway.
Gearboxes fitted to the GTST Skylines are almost identical in strength and design to the GTR gearbox, but without the transfer case. I believe GTST gearboxes usually go for about $1500, ratios are 3.214, 1.925, 1.302, 1.00, 0.752 They are a lot more common than the R154, and probably comparable in size and strength, but a lot easier to come by.
As is known here, the H151F gearbox fitted to the GXL 4WD is extremely strong, and has a transfer case with a central diff for full time 4WD, but the gearbox ratios are truly horrible. 4.08, 2.94, 1.49, 1.00, 0.881
I have no idea if the R154 Supra box can be adapted to the 4WD transfer case, or if the gearsets can be changed over directly between the two boxes, anyone here know for sure ? The R154 ratios are excellent 3.3, 1.95, 1.34, 1.00, 0.75 very similar to the GTR box. I have no idea if this is at all even feasible, but it would be a very expensive job to buy both gearboxes, and then swapping the parts across may not even be possible ??
Staying with Toyota bits, another freaky idea might be to use the new 5 speed 4WD automatic box from the GXL, fitted with a clutch. It has the good centre diff, and would certainly be strong enough, and the ratios are a lot closer than the manual gearbox. 3.520, 2.042, 1.436, 1.00, 0.716
Being an electronic auto it could be driven like a manual by using the clutch, and even by changing gear with paddles on the steering wheel as in a 5 speed sequential. For drag racing no need to use the clutch at all (maybe) except at launch.
How about the new 4WD Holden Monaro from HSV with the 300Kw LS2 engine and fitted with the Aussie Tremec five speed. It has a centre planetary differential that splits power 68% rear 32% front. The Tremec is damned strong, has good ratios, and the transfer case is undoubtedly pretty good too. I believe this same identical transfer case is being used in some Ford 4WD vehicles, but not sure exactly what.
Dellow may be able to supply a five speed Tremec with that transfer case already fitted to it, I have not checked with them yet. Chances are they are supplying HSV with theirs, so maybe it is now a standard item for them ?? Dellow no doubt can also supply bellhousings to fit the Tremec onto just about anything.
Most if not all the old 4WD transfer cases had no centre diff at all, you used locking front wheel hubs to go into 4WD, and unlocked the hubs for RWD. Not possible to drive it on bitumen in 4WD for too long without killing something in the transmission.
I have been looking at this 4WD problem for quite a while. The challenge is to find something strong enough, with good close ratios, and that has a proper centre power splitting centre differential.
It is difficult because all the really strong off road boxes have crappy ratios for a high powered V8 road car, or they don't have a proper centre diff.
