can I do this?

Back in july 2002 I paid a old friend $4800 to build me a diablo replica chassis. Then months later I sent him $3200 to do more work on the car. Then in 2004 I sent him another $5000 to help him out and put more work into my car. Now after all the promises that he made and changes on his part for the last 4 years I have nothing for what I paid for. (this is the short story) I have been helping him by storing these diablo bodies at my house and delivering them to him, and this last trip I kept one of these diablo's that is worth what I paid him in total $13000. He has said to others that he doesn't care about me or my car. Do I have a right to keep this diablo body which is an untitled piece of a car to sell and to make up for my loss? I want to write him a email and tell him that he has a week to refund my money or else I will keep the car and were even. I live in Pa. and he is in Louisiana. What is the best way to do this. Also I have no contract with him.

The money you paid him and the body you're keeping are separate issues. You have no right to keep the body. You'll have to sue him in court and prove that you didn't just give him the money to help him out and expected it to be paid back.