Fuel stores the potential energy that gets combusted and eventully makes the car move. To move the car faster you need to convert more chemical potential energy into mechanical kinetic energy (ie make it more efficient with the same amount of fuel) or alternatively let more fuel and air into the engine to combust (which is gonna be inevitable if were talking a 10 sec car).
Getting a car that runs 14s into the 13s could be done by making the engine more efficient (ie aftermarket ECU) without a significant increase in fuel consumption, but to get from 14s to 10s is gonna require a shit load of fuel to produce the power required hence making it a crap daily driver (just one of the reasons anyway).
I hope that makes sense...