Quote:
Originally Posted by pgfpro
That would be awesome but I don't think it will do it. For some reason 60mph is the cars most efficient mph??? I think it has to do to the very large intake ports and intake runners? I think it needs the velocity to work with the ultra lean burn?
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Definitely possible. Running the engine slowly and at low load works great on tiny economy engines with low valve lift, but for engines with greater "breathing" capability combustion efficiency can be a serious problem.
Porsche said that they were able to decrease idle fuel consumption by 20% when they moved from fixed cam profiles to Variocam Plus, and that was with low duration cams (high pumping losses).
My own FR-S has this problem too, below 2000rpm the efficiency drops like a rock. I can drive at 50mph and get 48mpg, or I can do 60 and get 42mpg. Even dropping the speed to 40mph, I can't really break 50ish. If I'm going 35mph, dropping down to 5th gear and 2000rpm engine speed vs. 1500rpm in 6th doesn't even drop the mpg by 10%.
Increasing cam overlap by just 5 degrees to introduce a little bit of EGR past what it was designed for from the factory caused some misfiring and a massive drop in fuel efficiency.
I imagine on your older engine, the engine could be struggling to burn the mix quickly at low speed.