Turbos are hot right now. Seemingly every segment of the car industry has at least one turbo engine on offer; twin turbos, once the realm of exotic supercars, are now available on pickup trucks and family haulers. In 2012, BMW upped the ante with a triple-turbo inline-six diesel engine for the European market. But too much is never enough, apparently. Rumor has it, BMW is readying a new diesel inline-six with four turbochargers.