Not enough... Seriously though I'm not positive, but I think their may have been more than one engine for the chevette, I know they made a diesel one at some point. the wiki for it claims between 53 and 70 at the wheel... I personally find that hard to swallow haven unfortunately having to drive one once...
Horsepower? THAT'S funny... hahaha....and yes there was more than one engine.
I own a 1980 chevrolet chevette. it makes somewhere between 80 to 100 horses. and yah its definitly not enough. gets great gas mileage though.
I have an 82 5spd diesel, it has like 60hp max, but gets down the road just fine. It cruises at highway speed (70) just fine, and if you keep it under that, it gets about 42mpg! It also will haul a deceptively large volume of gear!
(I bet the automatic transmission cars are real dogs though!)