It's a good idea in general, but the reason that these automotive forums have persisted virtually unchanged since 1998 is because they're sitting on a tremendous knowledge base that you can search.

If you can figure out a way to get these forums to migrate to your platform (yes, make it a platform), then I think you're on to something.

The other option is to just create the communities from the ground up and let the users fill in the gaps in knowledge.

People tend to have particular tastes when it comes to cars, so I think it's good to form communities around makes and models early on, or more general categories like hotrods or european sports cars.

Of course, I usually only go to car forums when looking up how to do a repair or something on my own car. It's a classic Saab, so the forums are simply the best place to get information on repairs.