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Old 05-30-2010, 05:35 PM   #21 (permalink)
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with the scanguage I've noticed accelerating fast halves the MPG figure i get when accelerating conservatively. Mind you that MPG figure is >10 MPG in a car capable of 30 mpg, so IDK. Might play with the thing sometime when i have the time.

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I think you missed the point I was trying to make, which is that it's not rational to do either speed or fuel economy mods for economic reasons. You do it as a form of recreation, for the fun and for the challenge.
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Old 05-30-2010, 06:05 PM   #22 (permalink)
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No love from "goose-ing" the throttle

I don't want to shoot down anything yet, but I've tried a tank of "jackrabbit starts" (pre scangauge) and I'll tell you that it burns a heck of a lot more fuel in the long run than normal acceleration. Maybe if I was going on the freeway for an extended period of time that might work, but usually I am only going a mile or two before having to stop for something. I can verify this from my scangauge, from about 20-60 MPH I can see anything from 3-5 MPG (75% throttle) or 12-22 MPG (15% throttle). Without directly measuring the volume that has flowed, I can't say conclusively, but given the chance (and a fat foot), this Jeep can eat a gastank quickly. Hope this helps more than confounds anybody

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Old 05-30-2010, 07:11 PM   #23 (permalink)
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with an automatic trans, the jackrabbit approach seems less likely to work.

Reason being, the greater the difference between the engine speed and the transmission input shaft speed, the more losses are occuring. When you gun it in an auto, the engine immediately revs up and starts sucking more air and gas, and the transmission and wheels have not increased speed at the same rate.


The trick with an auto is finding a balance between bsfc peak and increasing losses in torque converter slippage. I think that takes some feedback.
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Old 05-30-2010, 07:38 PM   #24 (permalink)
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In an auto transmission of the older general types (not CVTs, 8 speeds, transmissions that learn the way you drive, etc.), you want to find the minimum speed for an up shift first. Then find the greatest amount of throttle position you can give it without delaying the up shift.

I find that normal acceleration of traffic (at least around here) is pretty good. Your driving tactic in any auto transmission is to get into the highest gear the quickest, as a general rule.

Also try to minimise downshifting if you find you need to accelerate.

If you live where there are some grades, that are not too steep, you can pulse slightly up the grade and then semi coast down the grade and possibly improve your mileage.

The wife's Rogue and my Insight both have CVTs and they are different. The Rogue will accelerate up to 45 MPH at 1400 RPM without the RPM changing. The Insight can go from one stop to another with very little average MPG loss if you accelerate gradually and use regenerate about twice as long as it took you to get to speed.

DFCO is also a good tactic in an auto, if you have to stop. I find much of the art of getting good mileage consists of taking a lot of time to come to a stop. Of course avoiding stopping altogether is better, but with 46 traffic lights on my daily route you will always get nailed by a few of them.

One stretch of 4 miles on my route is about a light every .3 mile. If you do not average 47 MPH the lights will get you, even though the speed limit is 45. Go 45 and you will hit 8of the twelve lights yellow, until you catch one of them and then you start off at the beginning of the light timing window.

I don't use EOC in my cars. It could get better mileage possibly, but in the VX you are better to just use lean burn and stay in 5th gear at any speed over 30 MPH. I will coast down any grade that allows me to idle at 450 RPM and about .125 gallons fuel per hour. Coasting in the VX means your are getting 8 times the speedo reading in fuel mileage. EOC kills the lean burn feature for about 30 seconds after a restart.

I could probably get better mileage with EOC and no lean burn, but my average speeds are usually close to 40 MPH or higher.

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Old 05-30-2010, 09:00 PM   #25 (permalink)
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Quote:
In an auto transmission of the older general types (not CVTs, 8 speeds, transmissions that learn the way you drive, etc.), you want to find the minimum speed for an up shift first. Then find the greatest amount of throttle position you can give it without delaying the up shift.
That's exactly what I did this tank, and I only managed upper 27s. Doesn't seem like it does much good for my car.
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Old 05-30-2010, 09:36 PM   #26 (permalink)
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problem is that an upshift means more torque needed to turn the transmission input shaft, and more converter slippage.
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Old 05-31-2010, 12:01 AM   #27 (permalink)
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when I come off the dirt road I live on, I generally have to climb a roughly 5% grade that lasts nearly a mile. It's a conundrum for sure. Do I accelerate gently and never make it to 4th gear or do i hurry up and get into 4th before the hill gets too terribly steep? Once I get to 45 or so I can hold 4th, but the whole time I'm accelerating I'm climbing for the most part. I alway balanced jackrabbit with granny and chocked up the extra fuel spent on getting the tranny up to temp so that the torque convertor can lock in sooner.
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I think you missed the point I was trying to make, which is that it's not rational to do either speed or fuel economy mods for economic reasons. You do it as a form of recreation, for the fun and for the challenge.
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Old 05-31-2010, 09:04 AM   #28 (permalink)
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unfortunately climbing a hill is one of those activities that should put you closer to bsfc peak for a typical vehicle (allowing you to store energy in altitude for a nice glide later while running near peak efficiency). I think the only solution (short of a manual swap) is to override gear selection and lockup so you can climb in the highest gear that works without spinning the converter.

its called ecoMODDER for a reason
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Last edited by dcb; 05-31-2010 at 09:13 AM..
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Old 05-31-2010, 10:47 AM   #29 (permalink)
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On my Jeep, I tightened the TV cable on the tranny up a little about a month ago. With the same amount of throttle off the line, it now shifts about 150 - 200 rpm later than before. However, due to reduced torque converter slippage, mpg remained the same, while firming up the shifts a little.

The smaller your engine is, relative to the vehicle, the slower you can accelerate efficiently. With my huge displacement in a 4200 lb vehicle, I can basically idle up to speed barely touching the gas, but it's inefficient. I'm better off getting on it a little harder and letting it shift around 2100 - 2300. If I crawl around letting it shift around 1500 - 1600 (such as being behind slow people downtown), I get significantly worse MPG.
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Old 06-01-2010, 10:03 PM   #30 (permalink)
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Wow. I thought I was doing pretty good getting 50-60 mpg in my civic and I'll tell you what, I accelerate like a turtle and use the least throttle I can to get where I'm going!

I'm assuming this is a complicated issue, where there will always be a wide range of results in different situations and especially with different vehicles.

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