In the new “N” models of the 71 series basic changes were made in the injection system, combustion chamber, compression rings, and oil control. A differential needle valve replaces the crown valve in the injection system and provides improved combustion. Use of higher compression ratio piston and narrow compression rings have added additional flexibility to the series 71 engine. These developments resulted in the N models achieving greater fuel economy, improved oil control, practically clear exhaust, and improved light load and idle compression.