I've got my eye on a machine that will do a 600mm cube, which should be plenty big. I think the biggest issue is warpage of the large pieces that you want to print. If I could get away with printing PLA, I don't think it would be a big problem, but PLA melts at too low of a temperature for any engine application. ABS is good to 270F or so, which ought to be OK for an intake, but it tends to warp. I bought a spool of the ABS plastic used in the printers and soaked it in race gas and pump gas for several days, and it held up, so I think it will be OK with fuel. I'm currently experimenting with a smaller 3D printer to get the hang of it, before I spring for the big one...