I'm sure there were rules for the concept of racing in D20 Modern, does anyone have a fair idea how it worked or which magazine it came from. Initially I had thought that making opposing pilot or drive checks factoring the speeds of the opposing objects would determind whether you pass or not but maybe the other rules have more streamlined it.

What is the "situation"? How many racers? Are they racing against the clock or against each other? Is it a circuit or a distance race? Do they all have the same, or different, vehicles or are they running or skiing? etc..

1. a racing circuit in the future in which racers pilot advanced racing jets through a digitized racing environment
2. Not established yet but looking at around 16 overall, this is of course not the player count just all the racers
3. It varies, usually against themselves
4. Mostly they're the same though some have a few gimmicky parts and attachments

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.

Rats, I was hoping for a bit more than that, though I guess that's also what I was expecting.

Simplest way to do it: Straight up skill check.
Slightly more complicated: Compound or multiple skill checks (what mkooper was saying).
Way more complicated: OK, so you're at the starting line. {spot} The guy next to you is readying a concealed blaster in your general direction. {spot} Last night you saw him wander past someone else's vehicle and pull a hose.{knowledge(local)} He's a notorious cheat. Roll the skill check for starting your vehicle and your initial acceleration...