The name Miller-Cycle comes from the American Engineer, Ralph Miller, who patented his version of the forced Otto-cycle in the 1940's.  While similar to the conventional Otto-cycle engine, the Miller-Cycle engine has two main differences:

• It depends on a Lysholm compressor (click on the picture below for full specifications)  Note the conversion: 160kPa = 23.206 psi.

• The Miller-Cycle engine leaves intake valve open during part of the compression stroke, so the engine is compressing against the pressure of the compressor rather than the pressure of the cylinder walls.  the result is increased efficiency at a level of about 15 percent.

There are basically four means that the Miller-cycle uses to obtain its increased efficiency.

• Smaller engine (lower displacement - 2.3 Liters)
   

• reduced compression stroke and pumping losses
  (from late closing of the intake valve)

• cooler intake charge (intercooled air)
   

• combustion improvements

The 2.3 Liter Miller-Cycle engine found in the Millenia S is known internally as the "KJ" engine, while the base 2.5 Liter is known as the "KL" engine.  The Miller-Cycle engine provides 40 additional horsepower while achieving better gas mileage than the base engine - 20/28 vs. 20/27.