The search for fuel efficient engines that also offer good performance and fuel economy at moderate cost prompted the development of the Split Port Induction (SPI) concept at Ford Motor Company. Ford has upgraded two families of 2-valve engines, the 2.0L CVH 14 and the 3.8L and 4.2L Essex V6's, with the Split Port Induction concept. SPI offers an improved WOT torque curve, better part load dilution tolerance for fuel economy and superior idle combustion stability. This is accomplished by dividing the intake port into two passages and inserting an intake manifold runner control (IMRC) valve into the secondary passage. The opening of this valve determines the level of in-cylinder charge turbulence and volumetric efficiency according to engine operating conditions.The development of the concept and the improvements resulting from its application to these engines will be described and discussed.