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Old 03-06-2013, 01:17 PM   #1
Amdkt7
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Lightbulb Debating acceleration techniques

It seems on this site most are using very slow acceleration to maximize FE. On one or two other sites talk about using 1/2 or more throttle to operate the engine in it's most efficient zone (reduces pumping losses).

I have just purchased my 2013 Yaris and just finished the first tank of gas, so it's too early to begin testing, however my Kia Rio seemed to not care how gentle I drove it, or how hard I drove it, it always got about the same mileage.

Now, with the Ecometer on the Yaris I can see the effect of heavy acceleration directly and it is interesting to note that more pedal gives a heavy hit, but using about 1/2 throttle gets me up to speed much faster, when I can then drop back to light throttle.

The idea is to operate the engine in the best zone for efficiency, which is around 1/2 throttle, keeping RPMs low at the same time.

So, using the heavy foot approach the Ecometer shows a hit on instant MPG, but for a shorter time. Using a very light touch will take a less hit, but will stay in that mode for a longer time.

I have no idea which method would work better. My Kia did not seem to care, it always sucked (28-33 MPG). I'm wondering if anyone has tried both methods. I rather like the 1/2 throttle, low RPM method as I get going faster, and nobody is cussing at me.
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Old 03-06-2013, 01:32 PM   #2
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I am not sure how the Yaris is setup first of all.

This has been discussed indepth over at gassavers.org (I am a member there).

In a stick shift, it is better to get into top gear as fast as you can. In an automatic, it is better to get your torque converter to lock up as fast as you can. That leads to more pedal. The problem with that is that most cars go into fuel enrichment if you give it WOT which is probably what you are talking about. That is when your A/F ratio goes from 14.7 (or there abouts) down to like 12. Some newer cars use wide band O2 sensors and actually always stay in closed loop and never go into fuel enrichment.

I found on my cavalier (my other car) that it was somewhere around 3/4 throttle response when the A/F ratio would drop. My goal was to start off giving 3/4 pedal until I got up to speed. That seemed to net me the best mileage that I could get.

generally speaking, a stick shift yaris usually does around 40mpg. Not sure about the automatic.
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Old 03-06-2013, 03:32 PM   #3
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I'll go check out the info over at gassavers.org.
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Old 03-06-2013, 03:40 PM   #4
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I started a thread over there a few years back (maybe 3 or so) that was entitled "gunning it for FE" or something like that.

I will say that the traffic there in the past year or so has declined sharply. The web traffic/postings over there seems to go up with the price of gas. Makes sense.
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Old 03-06-2013, 08:53 PM   #5
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you'd really have to try both and figure out what works for you. There is so much difference in driving terrain alone that what would work for me might not work for you.

I live on a main road, and it might take 1/8 of a mile to hit 50mph, which is the speed limit. I don't rev the car above 2000rpms, I don't press the pedal down very hard at all.

I do almost always get at least 36 mpg while driving very short trips, at speeds almost always 50mph or below.

The one thing that seems to really make a difference to me for the Yaris is rpm's. Allowing the car to rev between 2000 and 3000 rpm dropped my gas mileage. I can't come anywhere near putting the pedal to halfway before I hit 2000 rpms in every gear.
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Old 03-06-2013, 09:30 PM   #6
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In a stick shift, it is better to get into top gear as fast as you can.
^^^^^ This is what I do.
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Old 03-06-2013, 09:43 PM   #7
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There is so much difference in driving terrain alone that what would work for me might not work for you
^^^^^ This. The terrain here (flat + gentle hills in a few areas) is quite different from where I lived when I first got my Yaris (Marin County,CA). The topography here (in addition to fewer traffic controls, traffic flow, etc.) allows one to achieve better fuel economy than in Marin pretty easily.
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Old 03-07-2013, 02:57 AM   #8
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I believe, in general, it is true for any car that you should accelerate briskly (not WOT), short shift a bit and get into the highest gear you can that does not result in lugging the engine. So many magazines and tv shows (Mythbusters is one, I believe) have run tests and it seems that they always get the same result: reduce time spent accelerating and get into the highest gear you can. And yet, there are still people and organizations that say to accelerate smooth and slowly...

Oh, and make sure you drive with your tailgate closed on your pickup trucks!
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Old 03-07-2013, 08:30 AM   #9
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Pickup trucks, Camper shell sloped at 10 (not mine, btw)

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Old 03-07-2013, 10:46 AM   #10
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I'm starting my second tank of gas. So far averaging 37 MPG, average speed is 48 MPH. This is one and a half trips to work, going home is down hill, so tonight my MPG will probably pick up some more. I travel 5 miles on interstate at 70-75 mph, then 15 miles around 45-55 mph. Around three miles is a long slope with an elevation change of 300-400 feet. Part of it is steep enough that I can hit 70 coasting in neutral. Coasting in gear costs too much momentum. Going up the hill I had to drop to 50 mph in 5th gear to keep the Ecometer above 25 mpg.
I'm trying to accelerate more briskly, often traffic ahead of me limits it. So far I try to shift at around 2400-2600 rpm, but get into top gear as soon as I reach the speed limit, then go easy. The Ecometer will show terrible numbers (8-12 mpg at times, but the gear shifts are happening so quickly that it's hard to get a good reading. Often will see 99.9 mpg during shifts. I don't really trust the Ecometer under those conditions.
I can't wait until the break-in is complete and I can put synthetic oil in it.
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Old 03-07-2013, 08:12 PM   #11
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Quote:
Originally Posted by Yaristeve View Post
I believe, in general, it is true for any car that you should accelerate briskly (not WOT), short shift a bit and get into the highest gear you can that does not result in lugging the engine. So many magazines and tv shows (Mythbusters is one, I believe) have run tests and it seems that they always get the same result: reduce time spent accelerating and get into the highest gear you can. And yet, there are still people and organizations that say to accelerate smooth and slowly...

Oh, and make sure you drive with your tailgate closed on your pickup trucks!
Briskly is a bit of a misnomer though. In the Yaris you don't need to floor it to accelerate enough to shift in the next gear. I doubt I ever get to 1/4 throttle in my car.
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Old 03-09-2013, 10:49 AM   #12
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Twice a day I have to enter a highway and get from a literal standstill to full traffic speed and all across the street to the leftmost lane as fast as possible while weaving through other vehicles. Yeah, I shift to third as fast as possible and then stay there until I run out of acceleration. Most other times, I can coast with me barely feathering the throttle. Also, yes, if you do have a manual, you want to burst through the gears as fast as possible. Still get 35 mpg all city and city highway driving, haven't had a chance to do any noticeable highway driving yet.
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Old 03-09-2013, 10:44 PM   #13
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Quote:
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Twice a day I have to enter a highway and get from a literal standstill to full traffic speed and all across the street to the leftmost lane as fast as possible while weaving through other vehicles. Yeah, I shift to third as fast as possible and then stay there until I run out of acceleration. Most other times, I can coast with me barely feathering the throttle. Also, yes, if you do have a manual, you want to burst through the gears as fast as possible. Still get 35 mpg all city and city highway driving, haven't had a chance to do any noticeable highway driving yet.
LOL. I read read the first sentence (without looking to the side to see who wrote it) and thought 'that sounds like Dallas'.
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Old 03-09-2013, 11:14 PM   #14
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LOL. I read read the first sentence (without looking to the side to see who wrote it) and thought 'that sounds like Dallas'.
It's Dallas

On the other hand, when I'm NOT forced to balls to the wall just to merge into traffic and get into the correct lane, I often skip a gear when switching from accelerating to coasting, most often I skip fourth.

Last edited by Kar98; 03-10-2013 at 01:24 AM.
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Old 03-10-2013, 06:34 AM   #15
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Yes, I will often skip 4th.
Yesterday I did some driving on a long steep hill, which required 3rd gear. I was able to try slowly pressing further and further on the gas while watching my ecometer. More gas was not resulting in more speed, and after about 1/2 throttle my MPG began dropping from around 20 to 17 mpg.
I think that every situation is different, sometimes it might be best to speed up very slowly, but more often it makes more sense to speed up more quickly, following the golden rule "keep the RPM's LOW".
Yesterday I was averaging 42 mpg, although the roads I was driving on were perfect for FE.
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Old 03-11-2013, 12:40 PM   #16
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Conventional wisdom says that when a person guns the accelerator with quick takeoffs, you then lose MPG. And when taking off at a snails pace, you get better MPG! Actualy, a car can get poorer gas mileage going slow on takoffs because the car stays in lower gears for a longer time, preventing it from upshifting to a higher more efficient gears. This applies to automatic transmissions, and not manuals. I have a manual and I shift through the gears very fast and up to 5th gear by 30 MPH. All my shifts are under 2,000 RPM on flat surfaces, up a hill slightly more. I'm considered as a slow take-off starter, but not a turtle creeper who drags on the gears. By using this gear shifting technique, I'm able to get optimal gas efficiency.

Cheers!
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Old 03-11-2013, 03:12 PM   #17
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So far it makes sense to me try to get up to speed more quickly, no sense poking around in the least efficient gears. Observing my Ecometer as well seems to be indicating a bit higher effeciency above 2,000 RPM, but it is hard to tell with the two second or so lag in the reading, and on level ground you are only in the lower gears for a few seconds. FE for my second tank of fuel was 40 MPG.
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Old 03-11-2013, 04:21 PM   #18
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that is the big reason I like the scangauge as I can set it for "trip" MPG and it tells the tale a little better and quicker. I can drive to work using different styles and get a descent idea of what works better.

ecometer is a good start though.
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