Always a great topic
consider that BMW did an experiment in late 70's...production in mid 80's...
took a 3200 lb 5 series, 4 door....
wanted the smoothness of in line 6, with economy of 4...
developed a 2.7 liter low RPM, high torque , 121 HP 'eta' motor....33 MPG
to compete with 1.8 to 2 liter 120 HP 4 cyl, running at higher RPM, more
vibration. actually got a little better mpg with the 2.7 liter 6 making
same HP as 2 liter 4.
consider that the car requires a fixed torque at rear wheels at a given
speed...and hence HP...to cruise, that is the sum of friction and
aerodynamics, tires, etc. so , the JEEP may need 12HP to go 60; an MR2 7
HP; the 5 series...10 HP;
whatever the engine, it needs to make that HP to keep the car going at the
test speed.
so, the question is, what's the most efficient way to make 10 HP (or
whatever). the answer is lowest RPM with wide open throttle. Lowest RPM
minim's friction losses that go up rapidly with RPM, and WOT allows you to
get max air/gas in for that engine speed/ friction overhead; less than WOT
"wastes" some of the friction by restricting max HP
R&T did a similar test showing that accel with WOT and shift early (low rpm)
to get up to speed, rather than part throttle and higher RPM shift to get up
to same speed in same time. (In other words, ACCEL at a constant rate to a
given speed, it is done more efficiently at WOT and low RPM/ short
shifting.)
Consider that this sounds a lot like a diesel...
cheers
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