Those with a passion for torque were disappointed when it became clear that Audi was unlikely to ever build a production version of the R8 V12 TDI that was shown at the 2008 Detroit Auto Show. Now the automaker has come back with a new R8-based concept that puts the diesel to shame. The new e-tron packs four electric motors and a lithium-ion battery pack with a fairly tame-sounding 313 hp but an insane 3,319 lb-ft of torque. The run to 62 mph takes...