the transmission in s chassis is very strong. they are the same tranny used on 2.0 and 2.5L skylines, na z32 300zx too. 600hp will break them eventially. but its far from common.
when a tranny is built up, the replace the input shaft and all gears with wider straight cut gears. they have more surface area when the teeth are meshing together, hense the load is spread out over the entire tooth.
by the way, PAR makes upgrades for this tranny
shaun