[pgfpro]

sword_guy8

IMO I think what you are seeing when in high gear is a low air velocity at the intake port that creates poor fuel atomization. The 3rd gear has a higher rpm that increases port air velocity while still maintaining good load or higher MAP pressure and reduces pumping losses.

On my car I can maintain any A/F ratio at any load due to my engine management system. I have done some testing to see how far I can load the engine at different rpm's. I have large intake ports that flow great numbers for HP reasons but suffer when it comes down to low rpm high load fuel efficiency. So there is a point on every engine where it has a happy place when it comes to load and rpm.