[89IROC&RS]

the problem with the stock rear end and transmissions is that they were designd for 170-250hp, so they built the units to handle that power for as cheap as possible. that means they skimped on material in weak areas that they could get away with, such as clutches in the trans, and the strength of the metal and bearing caps in the rear end. so when you start upping the power, the actual metal peices of the rear end will break, as in cracking the ring gear, or stripping teeth off of it. you can actually fracture the housing of the carrier, stuff like that. for the trans what happens is the clutch packs will wear quickly, and fail early. with a manual, its much the same stuff as the rear. the metal is too weak, and will break gears, shafts, or strip teeth off. think of it as a small electrick motor, all you need are cheap plastic gears. throw those same gears on a gas powered lawn mower, and youll understand very quickly why the stock units fail under load.