I used the Communities link and searched for cars and DIY and engineering and subed to any of the ones which seem to have even a little bit of traffic (in the hopes that maybe things would increase eventually). For car ones, literally just "Cars" and "electric vehicles" are the only real one I bothered to sub to. Tried looking for Subaru or WRX stuff and that came up basically empty. For tinkering there is "3d Printing" and "woodworking" but I think the woodworking one is moving servers so it might disappear. Also "Machinist" but there's no traffic in that one. Which is the case for far too many of the ones that come up.