Just looked at this on the ride home tonight. I'm at exactly 2k @ 60mph, if i lower it in fourth, my rps shoot up to 2800 - soi still don't see how that will save gas on an NA engine.

 

as far as the higher revs = better mpg, there is some truth to this, as the engine is at its 'peak', meaning that it's 'freewheeling' (if you will). when the engine has to work harder, it uses more fuel. take of from a stop and upshift fast. with more load on an engine= more fuel. i know on my Rotax 377, i get better mpg at 8k than i do at 5k. its finding the sweet spot in the rpm range

 

its like riding a bicycle with multiple gears...you could differentiate how much energy you are using to pedal when changing different gears.

 

Good to know I'm not completely losing my mind. Anyway, went out for a very long drive yesterday, I definitely get better mpg in 4th gear going 60 than I do in 5th on route 2. I did manage to make some sense of it however, route 2 isn't the flattest places to drive and it's much easier to keep my vehicle at a constant speed/the same rpms when it's a little higher than it is lower (while in 5th).

 

dont complain at 3k im at 70 with my cooper s and thats a 6spd

 

generally a 4 stroke engine will use the most gas at its maximum torque. and from what ive seen its at like 1750 rpm somehow. so driving at a higher rpm using less trq and just more hp you should theoretically get better mpg. must be why u get better mpg's in 4th gear then 5th gear

 

I think it comes down to a ratio between how many ms the injectors are open and final drive speed.

Under a moderate load in 5th gear, like during a gentle ascent, the throttle angle will be much greater than when in 4th. That larger TA with its lower vacuum demands more fuel even though the final drive speed is the same.
Ascending a 2% grade or more, it makes sense that 4th might get better mpg despite the higher engine rpms.

Was bored and plotted the range of ratios represented here:

99 1.8TQA 60 2400 1.50
01 1.8TQM 70 3000 1.40
2.8QM 70 3000 1.40
99 1.8TQM 65 3000 1.30
96 2.8QA 59 2000 1.77
99 2.8QM 65 2700 1.44
2.8 12V 60 2500 1.44
99 2.8QA 75 2700 1.67
00 1.8TQ? 60 2500 1.44
99 2.8QA 60 2000 1.80

I'll post up mine when I know for sure but I think I am right @ 2000 also. My understanding is the 1.8T has a different final drive ratio than the 2.8 does. Manuals appear to be showing more engine turns per MPH as well.