Quote:
Originally Posted by Panther140
Let it downshift on the way up the hill. Thats okay. The point is to get as much of the work done with the engine near WOT as possible. If you have a manual transmission, pick a gear that keeps you near peak torque, then open the throttle all of the way. If you have an automatic, it will still run more efficiently with the throttle at WOT. If the RPMs rise too high, let off of the throttle quickly to let it upshift. Then resume WOT operation.
If there is no hill around, you have to accelerate on the flat ground. If the grade isn't steep enough to have a significant impact on the amount of potential energy instantaneously aiding or being acquired by the vehicle, then you will most likely only see negligible gains from leveraging them with strategic pulsing and gliding.
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So, although I've been arguing for accelerating up hills, my real-world experience shows (after a certain point) a huge FE penalty from downshifting. My Insight has peak torque (from gasoline alone) at 5000rpm, but accelerating in low gear, high RPM reliably murders economy with this engine, despite BSFC charts not showing a cliff.
I drive the same routes frequently (hundreds of times over the last few years) so I've had a chance to do a lot of apples-to-apples comparisons. Let's say I have a 10 mile trip on the highway. I reset the fuel economy gauge before taking the on ramp, and check it again after 10 miles.
Pedal to the floor during acceleration but shifting at ~2000rpm and taking my time getting up to speed, I may arrive at my destination with 100-110mpg on the gauge, after 11-12 minutes of steady-state cruising at 50-55mph.
Shifting at ~3500rpm, I might arrive around 90mpg.
Taking 2nd gear up to highway speeds and shifting at 5000rpm, I'll be lucky to get my average up to 75mpg.
Redline it and it will take a long time to climb out of even the 30's with a result of the end of trip reading being in the low 60's.
I figure 10 miles is probably long enough that the greater rate of acceleration probably makes very little impact on average trip speed, so all I can think of to account for this is a serious drop in efficiency, despite what I can make of BSFC charts.
YMMV