Уоррен
It would be a good idea to maybe increase the "pitstop time" overall rather than every pit being between like 3-4 secs plus pit lane time, maybe the pit stop time could be between 3-10 seconds depending on fuel, plus then added pit lane time depending on the pit lengths. That way pit stops might become more important as people could underfuel to get an advantage out of the pit. Also might give an indication of a teams fuel level....
5 litres of fuel per second would seem like a decent number, obviously the first 15 litres would be free with the tyre changing, but 20 litres would be 4 seconds, 40 litres would be 8 seconds. It could encourage people to strategize an extra pit stop at certain circuits and in certain conditions, but at the same time doing this will discourage people from trying to make one less pit stop, which can also be a winning strategy.