if you have bent valves you will not get good gas mileage,how do you know you have bent valve ?? did t-belt break or did someone put a new belt on wrong and they bent.that's the only way to bend valves.the car will run okay with slightly bent valves but not great.most of the time it will idle rough & have lack of power.if you keep driving it with bent valves you will burn valves and possabley damage head.get it fixed right!! your mileage will improve.