I have been running an H-150 with (poorly) welded spyder gears for several years behind a Z-20 engine that I estimate makes around 165 to 170 horsepower. In fact, it was my daily driver for quite a while. I know the car saw some hard use while it was "on loan" at a friend's race shop a few years back and it seemes to have held up fine. I guess what I'm saying is, the H-165 should be more than adequate.