dumb question but i aint played rev rally in a while and i was wonderin how much gas is it for a 5 lap race again im talkin bout the demo rev rally track to........

Stick about 15% in and you'll be fine

do a full lap and press F12 then read how much it says per lap, maybe a % per lap or so you need to do the lap to find out the fuel usage, example 1.1%. multiply that by 5 laps and there you go. you may want to put in an extra % to guarantee a finish, incase you spin the wheels too much or wind or something.