About 500bhp/400ftlbs i would say. plenty of ways to make it stronger before going aftermarket though its like the evo box its basically on the limits from factory. mine is now good for well over 800bhp with all stock parts except the uprated output shaft.
Basically yeah there is a company that freezes it and warms it very slow, its called cryogenic treatment, the company i was told about is called frozen solid. the guy who built my box (very reputable in the evo world) advised that unless its a proper competition car the benefits wouldnt be worth the extra money. he said its better used for like engine blocks.
As for my box it has had the following.
New Uprated centre diff output shaft
New Uprated Shifter bushes
New Input shaft (evo 9)
New Uprated output shaft bearing
New Lower output shaft bearing
New 3rd gear syncro
New 3rd gear (Dual stage shot peened)
New 4th gear (Dual stage shot peened)
New 5th gear (evo 9)
New 3rd/4th hub
New 1st/2nd Syncro sleeve
New 3rd/4th Syncro sleeve
New 5th/Rev Syncro sleeve
New Input shaft bearing
New Input shaft seal
New 2x thrust washer
New 1 x thrust stopper
New 3 x preload shims (all perfect fit as he bought all of the remaining biggest shims from mitsi and skims them for a perfect fit)
Oil gallery modification
Both new 3rd/4th gears dual stage shot peened as they are the weakest gears and are prone to cracking.
Whole gearset Isotropic Super Finishing
Transfer box was stripped inspected and rebuilt with new shims, seals and uprated diff bolts also.
ISF is a process in which the gears go into a machine with a mix of materials which then basically vibrates and causes the gears to become smoother. the gears from factory are something like 16RA. mine are now around 2RA. RA Is the finish of the material. the company that did mine also do all the F1 cars components. basically the less rough surface means less friction, less heat, and less drivetrain losses.
My gearbox and transfer box ended up costing around £2250 and is worth every penny.
Couple pictures of the internals.
Twisted output shaft (bear in mind this happened at 315bhp! The power it was running when i forst got it)
Damaged input shaft, where 5th gear was sliding up and down ever so slightly rather than sitting solid on the shaft.
Wear on 3rd gear and new gear underneath.
Damage to synchro sleeves and new one.
Above pictures before ISF.
And some below of when they returned (pictures not the best)
Yeah fwd have alot less stress on gears which is good. If you ever want the ISF work doing let me know and i will speak to my guy and see if he will take them in for me. cost as far as i can remeber is circa £400 for a full gearset.
Yeah i like it too.
I was the same, i didnt think it would do much but you can actually feel the difference in gear changes. and obviously less stress and heat etc how can you go wrong. 400 is well worth it and the guy who built mine who is also the builder of norris designs boxes and 90% of the high powered evos about swears by it. this is a guy who bought a second hand gtr box to strip it down and write his own manual and inspect weak parts so he can make and sell stronger parts for it as nissan dont sell individual parts for the boxes and a new box is about 20k!