Can a pit bull outrun a greyhound and how close would it be?

If it was in the mood then biologically yes. A greyhound runs a 37-43 mph ( very rarely exceeds 40 mph, so 37-39 mph greyhound). A guinea pig runs at 39-47 mph, however such sprints can only last for 5-15 seconds. So the cavy could outrun the sighthound, but it would need a crevice to run into, and fast.