An automobile engine design by Volkswagen, available as of February 2001 in Passat models in Europe, with the United States to follow.
The layout is an extension of VW's VR6 engine, which consists of two banks of three cylinders, 15 degrees apart, sharing a common cylinder head. The W8 is something like two "VR4"s: four banks of two cylinders, in two pairs 72 degrees apart, with each pair sharing a head.
The current incarnation is 4.0 liters in displacement, producing 275 horsepower (202 kW), and 273 foot-pounds (370 Nm) of torque. Like the newest VR6 models, the W8 has four valves per cylinder, actuated by chain-driven camshafts.
To put it another way: Hold up your index and middle fingers side by side; suppose that's a little like a VR6, viewed end-on. Now make the Vulcan "live long and prosper" sign: that's a W8.
Performance data and facts from vwvortex.com.