I think the cheaper 3D printers use materials such as ABS plastic as their medium.
But have a look at the following videos and see what Koenigsegg of Sweden has been doing. Now possible to use titanium, stainless steel, aluminium as their 3D medium, and there is talk of carbon fibre.
Their twin turbo unit (one section is for high revs, the other for the low rev band) is featured and the internals were all assembled inside the case during the printing.
The world of 3D prototyping and printing has changed the automotive industry. Christian von Koenigsegg explains how his company takes advantage of the new 3D Printing technology, with where he feels the future of the industry is going. It allows him to save on tooling costs and enables him to be "competitive" with the big guys when he has small and variable volumes.
https://www.youtube.com/watch?v=Dw6cs7opvzA
https://www.youtube.com/watch?v=DNedUZxP8NU
http://www.youtube.com/watch?v=tcY9fBt_gWg