Why are 318's low HP and torque?

Sweet. More bang for my buck! I'm trying to decide what gears an rear end belong in the car with a 318? I have the stock 7 1/4 right now.
Keep an eye out for an 8.25 or 8.75 rear that's close enough to pick up. It may take a while to find but That's what I'm doing. Either as part of a parts car or separate. I look a few times a week and when I find it I'm gonna pounce. The gear choice is going to be your choice based on how you want to drive. 1/4 mile at at a time? or 50 miles at at time? Somewhere in the middle is always good that way you get some fuel economy but still fun to drive.