Optimal Acceleration AT&MT - Gas only

[Tweakfreak]

I did some searching to no avail on this topic. I have a couple of theorys and was curious what others have come across.

AUTOMATIC

Information: With an automatic you are in battle with the shift schedule programmed in the PCM. There is where that car will not up shift anymore w/out additional throttle. For me I have a 2.0L DOHC Zetec mated with a 4EAT transaxle. The most minimal acceleration the car shifts around 2100 RPM.

Questions:

• Are the minimum engine speed upshifts due to torque converter stall rate?
• Does this hurt efficiency since a lot of fluid passes threw the TC w/ out providing forward motion?
• Would a moderately quicker acceleration up to the same cruising speed be beneficial?

Theory: I feel that there is some balance between that absolute minimal acceleration and the point of open loop mode. A point where the torque converter is being used efficiently and FE reaps the rewards. I'm not sure if this is true but it kind of makes some sense.

MANUAL

Information: Of course the driver in this case and more control over engine speed and gearing.

Question:With a ability to upshift earlier, how early is too early?

Theory: This is vehicle dependent and of course its obvious that it needs to be something above idle. I'm just curious how much volumetric efficiency at very low RPM and very light throttle changes fuel economy on these kind of acceleration. Whats the general rule of thumb?

Thanks for the read,

Anthony

[99HXCivic]

There was a previous thread on acceleration and fuel economy. But I shift my 99 HX M/T at 4500 to 5500 rpm and still get good mpg.

[PaleMelanesian]

I shift at or before 2,000 rpm. I pay more attention to the target gear - try to land in the 1000-1500 rpm range.

[Shan]

Andrew, I am assuming you do not bog the motor or rather flood the motor with fuel at that low of a shift?

I have tried shifting at 2k but the motor seems to bog and I am currently shifting a 2250(around there) like Larry which helped me reach my 60mpg goal.

[PaleMelanesian]

2250 - That works. I TRY to keep it below 2000, but sometimes I do go that high.

If I'm really light on the throttle, it can gain speed from as low as 1000 rpm. That's low 20's mph in both your car and mine. I only go that low in certain places, of course. Any more throttle and it just rumbles more but doesn't move any faster. I figure that as long as it's not shaking, it's fine. I doubt flooding is a problem with fuel injection - I haven't had a bit of trouble with that.

[Tweakfreak]

I think there are a couple more variables to take into account. Engine load, engine speed, brake specific fuel consumption, pumping losses and EGR(or in my case exhaust VCT). I need to understand the relationship between these things to develop a better theory.

[PaleMelanesian]

Basically, at such a low rpm - 1000 or so - it only takes a feather touch on the gas to reach high load. Any more than that and you're not getting any more work done.

[nissynis]

FWIW, and this is surely car-specific, I upshift at about 1600 RPM. In my 5 speed, that drops me into the next gear at about 1100-1200 RPM. I'm only in each gear for a couple of seconds.

There definitely is some tradeoff, you are right. If you are nearly lugging, you can sit there forever trying to accelerate and only doing so slowly. This seems to me to eventually be inefficient, esp if the alternative is getting up to speed and then FASsing.

[lnmcmahan]

Originally Posted by Shan

Andrew, I am assuming you do not bog the motor or rather flood the motor with fuel at that low of a shift?

I have tried shifting at 2k but the motor seems to bog and I am currently shifting a 2250(around there) like Larry which helped me reach my 60mpg goal.

I have been expermenting with this lately, but I have found that if I shift in lower than 1400, say, and keep my load below 80%, my pulse length is too long, and I wind up eating all the mpg gain I got on the previous glide. There is definitely a sweet spot between low rpm and shorter pulse length. I'm looking for it!

Larry

[PaleMelanesian]

I know what you mean. I'm still not entirely sure where the sweet spot is, myself. I do know Wayne likes super-low rpm, and I can't touch his mpg.