All about U2

Design of NGK Block Coils

U2 coils generally can be divided in two different groups.

In this case, there is a dedicated ignition coil for each spark plug. An example for this technology is the U 2011 type, used in VW Golf 4.
It contains four independent coils which each of them supply one spark plug.

In this case, one coil has two outputs and thus supplies two spark plugs. This is called "wasted spark" or "double spark" technology. A double spark block coil for a four-cylinder engine therefore contains two coils. An example is the U2003 Type, used by Audi.

Clearly visible in the cross-section are the two ignition coils which have been integrated into a block coil.
Cross-section of a double spark coil:

With high quality coils, epoxy resin is poured into the inside of the block coil in a vacuum moulding process: This creates the ideal insulation, as a high density is guaranteed and no air bubbles can be trapped inside.