Shifting and Fuel Economy...

[gone-ot]

...FWIW, a lot of 2011 Cruze 1.4LT owners are starting out in 2nd gear by using the "manual" gear-selection mode of their 6-speed automatic 6T40 transmission in order to get into higher gears quicker for better fuel economy.

...YMMV.

[JeepNmpg2]

Originally Posted by Old Tele man

...FWIW, a lot of 2011 Cruze 1.4LT owners are starting out in 2nd gear by using the "manual" gear-selection mode of their 6-speed automatic 6T40 transmission in order to get into higher gears quicker for better fuel economy.

...YMMV.

Not to be a pain in the drain, but isn't using the torque converter (TC) in an automatic transmission about the least economical way to accelerate? I don't know the full mechanics behind it other than I've replaced one, but from personal experience I get easily 15% better FE after I feel the TC lockup.

- hill on my daily drive to work scangauge readout:
if left in overdrive, the TC doesn't lockupin 4th and at 39 MPH instant MPG is 10.6-11
If I put the lever down one position, it will lockup in 4th, at 39 MPH, instant MPG is 12.1-13

Just my 2¢

[SentraSE-R]

There's no contradiction here. TC slippage is a part of accelerating with an AT. If you can avoid one more gearshift and avoid lower gearing by starting in 2nd gear, you should get better FE.

[gone-ot]

...in addition to a "slush-o-matic" converter, the 6T40 also uses "dual-clutch" engagement control.

...it actually slips the tranny into NEUTRAL when you're stopped, then re-engages when you take your foot off the brake pedal and depress the accelerator.

...which produces two interesting idiosynchracies: (1) the car tends to roll foreward or backward if you stopped on a hill and (2) there's a noticeable hesitation/then slight lurch as the clutch re-engages upon take-off.

...and, YES, it's unnerving to new owners at first!

[orange4boy]

I'm with Arragonis on this one. Save the clutch.

And I say "manual TC lockup switch" to the rest of y'all. I'm such a pimp.

[skyl4rk]

I tend to give just a short blip of power in first and second, and a slightly longer blip in third, with the goal of getting to fourth and above as soon as possible.

I also try to roll through stops as much as possible to start out in second gear.

Be aware that while acceleration has an effect on FE, it is the coasting and stopping phase of driving where you can make the most difference in saving fuel.

[PaleMelanesian]

Originally Posted by skyl4rk

Be aware that while acceleration has an effect on FE, it is the coasting and stopping phase of driving where you can make the most difference in saving fuel.

I totally agree.

[Christ]

#1 -it makes more sense to accelerate with the engine at peak bsfc.
#2 -it makes more sense to accelerate smoothly in the highest gear without lugging the engine, under as much load as possible.Ee
#3 -remaining aware of your situation and using good judgement will tell you which method to use and when.

Most generally, I use first gear to get moving, nothing else. Once the speedo needle has moved, I shift into 2nd gear and begin accelerating. When I reach a speed in a gear that puts me at idle in the next gear, I shift. I do this audibly because I dont have a tachometer in my car.

In the smooth shifting arena, I'm a king. Often, people riding in the vehicle with me don't know that I've changed gears at all, except by seeing the movements inside the vehicle cabin. Up or down, I match vehicle speed to engine speed before engaging the clutch, IF I actually disengage the clutch to begin with...I often do not.

EDITED FOR CLARITY...

[JMac]

Christ,

#1 -it makes more sense to accelerate with the engine under as much load as possible.
#2 -it makes more sense to accelerate smoothly in the highest gear without lugging the engine.
#3 -remaining aware of your situation and using good judgement will tell you which method to use and when.

Wouldn't engine efficiency while accelerating follow a parabolic curve?

Obviously lugging is bad, but even at a speed where the vehicle is moving just fast enough to not lug the engine, say, 35mph in 5th gear on your average car. Let's say you want to accelerate from there to 50mph. In 5th gear, and assuming a flat road, one would have to press pretty far on the gas pedal to get decent acceleration (even for a hypermiler) at those speeds. Where as fourth gear, I believe, would get the car up to 50 much more efficiently.

So if #1 and #2 are true, then 5th gear would be the best choice if it doesn't lug. However if 4th gear is more efficient, then #1 and #2 are false.

Thoughts?
JMac

[Christ]

#1 and #2 are never accurate at the same time, hence the caveat, #3.

Depending the situation, it may be more efficient to use the highest gear and load the engine as much as possible, whole another situation might warrant leaving the car in a lower gear, allowing the engine to rev to it's peak bsfc area (usually where max tq occurs, also) before shifting.

Specifically, if you need to accelerate quickly, shifting at peak torque, same with uphill.
However, it's generally considered more efficient to ignore the bsfc curve and keep the engine loaded at let rpm, as fuel consumption is based on time(rpm) and power. The idea is to use the least power you can, at full throttle, so that LOD is as close to 100% as possible all the time. Technically, the closer you are to 100%LOD, the more efficient you're being with the fuel being burned.