You could always download a program a program and do it yourself (think it's RomRaider) but you'll still need to get the cable somehow. Either way if you want to make your car go faster I'll go ahead and say it YOU HAVE TO PAY TO PLAY.
It is kind of true about paying to play. But I believe that there are some free base maps either through the opensource forum or RomRaider. Cheap and modifying a car (the good and proper way) dont really go together.