Plenum & Injector Housing Porting

[Marc Haibeck]

Mercury Marine corrected the port mismatch problem in '93. It was part of the 405 hp upgrade. They CNC blended the injector housing ports 1.5" down the port. They also increased the plenum port diameter from 33 to 34 mm. That's why porting an early engine well will add 35 hp. Only 20 hp can be gained on the '93 and up engines.