i know wennys car is a drag racer albeit road legal nearly 600 hp and his cozzie has a barra and his wheelspins all 4 wheels for about 30 foot off the start line and it doesn't shit itself, that is the test for a 4wd box i think and his works time and time again. i would say buying a box rated for 300 hp and running massivly over was daft and asking for it to break if used to the engines potential.