SP.UI.ModalDialog.showModalDialog(options), so at that point you can pass the ID of the car item you are looking at the detail of, and use that in the New form of the review list to pre-select the car.
You can find lots of examples of how to embed scripts on SharePoint forms/pages and how to use
SP.UI.ModalDialog out there on the internet. The trickiest part might be figuring out how to read the args passed to the modal. The easiest solution I've found is to check for