Advice from the OldFart: Your buddy obviously has some sorts of feelings for this girl. He's protective of her. Could be an older brother thing or maybe it's more, but the fact is that he does not have an intimate relationship with her and therefore she's fair game. When you talk to him, start out by telling him that you're not just looking to bang her and that you are genuinely interested in her. Let him know that you will treat her right and if things don't work out you will end it properly as well. After that, simply tell him that you intend to date her that you hope it won't effect your friendship. He needs to suck it up.
If you are just looking to screw a good friend of your buddy, you're the jerk. If he's being a cock-blocker, then it's him.
She's a pretty girl, good luck!
[edit]?! I just realized where I was. Isn't this supposed to be about cars?