[FutureBoy]

I want to build a car more or less from the ground up. I can pretty much house rule a lot of it but in the terms of tires and, more importantly, engines it seems like actual stats might be important. Is there any reference to something like that in 4th ed that I missed?

[FastJack]

Check out Arsenal. It has a lot of rules on modifications and such for vehicles that should help up create a car from scratch.

DriveThruRPG
BattleCorps

[Dakka]

In terms of game stats your engine is likely to modify Handling, Acceleration, and Speed.