Lol, it's kind of weird. I'll try to explain it.
Ok, you know when you look at a car that's in your garage?? It'll say the horsepower number. In this case, it's 591 for the lancer. However, if you go into the settings option on the race menu, and chose an engine upgrade, it will give you a higher horsepower number then the one in your garage. In this case, it says 602. Even with a car that says 602hp, you can enter 591hp races. I have no idea why......