Well, all the variables seem to be based on skill and luck (dice) and gimmicky parts.
If gimmicky parts change the driver's skill then it does not add any other variable. If it adds a performance boost to the jets then adds another variable: equipment
In this case for each difficult manouver in the circuit you would make a roll for each racer with circumstance bonues (tightness of turn etc). The difference in the skill roll would indicate a forward or backwards performance of the racer, either in time or distance. A critical miss could indicate a crash.
For the jet perfromance variable you could take a constant bonus or negative for each jet in the straights of the circuit.
Multiply the total by the number of laps and you have a winner.