A concept engine developed by Volkswagen. Used only in demo and race cars for now, it demonstrates the immense amount of power VW is able to fit under a tiny hood. It's essentially the big scary brother of the W8, but with 12 cylinders instead of 8. Where the W8 is essentially two VR4s (which don't exist unto themselves) arranged at an angle to drive the same shaft, the W12 is basically two VR6s (which do exist, and until recently were the biggest engine VW produced for mass consumption), arranged in the same way. It has been manufactured in several versions, the most powerful producing an awe-inspiring 600 hp. This engine set the world speed endurance record, covering almost 8000 km in 24 hours. That's an average speed of 322.89 km/h.

Update: A 414 HP version of the W12 is in the Audi A8 in Europe, and it will appear in VW's new luxury vehicle, the Phaeton.