Is it a friend? I'm assuming not and I don't want you wishing that you never did this. Towards that end, because you're asking you almost certainly don't know

Is it a friend? I'm assuming not and I don't want you wishing that you never did this. Towards that end, because you're asking you almost certainly don't know how to properly retain a perfected security interest in the car. You need to determine if it's worth dropping $500-1K on having your attorney draw up the loan and security agreement and instructing you how to go about perfecting the security interest in your state.