assuming Danica Patrick is 100 lbs ,her car falls exactly at the IRL 1525lb ( which most do)minimum and the engine is putting out about 750 HP ........

Danica's engine/ car combination with her in the seat is using 1 HP to move 2.17 lbs

assuming Robby's weight is 200 lbs and again, his car is at the IRL minimum and 750 HP..........

Robby's car is using 1 HP to move 2.3 lbs, which gives Danica almost a 6% advantage in HP to weight. IRL rules are set up to try and avoid this situation, obviously they need a little work. In NASCAR and F-1 the driver's weight is taken into consideration when weighing the car.