If your engine is vibrating or sounding like it is stressed at speeds above 50 mph it's past time for an engine rebuild. Back when the Falc's were new people drove them 70 mph (speed limits were just going up to 60 on major highways) and I recall seeing more then one doing 80 on old route 66 in the California desert.
The real problem is that in the US we have had "big enigined" cars for so long that we have forgotten how to drive small displacement engines. We expect instant gradification (up to speed quickly) while people in other countries continue to live with engines of less then 2 liters and don't complain. "The times they are a changin..." | 
