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Old 12-04-2009, 07:08 PM   #21 (permalink)
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Originally Posted by 99LeCouch View Post
You could try letting the car roll a bit, then stabbing the throttle hard briefly. These are large cars, they roll very well.

Do you have the 3.4 or the 3.8?
I think he has the 3.8.

I think it has been said that most of the time, highest gear and lowest engine RPM's at cruising speed is the best combination to high MPGs.

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Old 12-04-2009, 07:16 PM   #22 (permalink)
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Originally Posted by JonnyG View Post
My method keeps you slow in 1st gear and then moderate acceleration throughout acceleration after that. By moderate acceleration, I mean that you should accelerate as fast as possible with the shift points staying around 2000 rpm. If you accelerate REALLY slow throughout, you're going to be spending too much time just short of the shift points, which wastes gas. Generally with a V6, anything over 2000 rpm is going to eat up gas quickly.

The only way to see the penalties of different acceleration is by using a Scangauge, but this is what has worked for me and several other people.
Alright good, so essentially what I thought. This does seem to make sense to me for an automatic transmission. Unfortunately I don't have an RPM gauge, so this is going to be pretty tough.
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Old 12-04-2009, 07:17 PM   #23 (permalink)
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Oh, and I don't actually remember if it's the 3.4 or 3.8. I can check though.
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Old 12-04-2009, 07:19 PM   #24 (permalink)
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my 80% statement is probably a little stretched. All I know is, I accelerate to the speed limit, and then let the TC lock up. I think it shifts at 2200 or so, I may start accelerating at 2000 and then see the mileage.
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Old 12-04-2009, 08:43 PM   #25 (permalink)
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I'd suggest trying a few consecutive tanks at approximately the same exceleration rate then try a new acceleration rate keeping track of what seems to be best for you and your car. Personally I have always benefited most by being light on the pedal and always keeping the rpm's as low as possible without overworking the engine, but all but one of my cars have manual transmissions. I have found that going just as light on the throttle as possible always works best for me and I've tried several different methods.
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Old 12-04-2009, 08:55 PM   #26 (permalink)
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Double checked and it's the 3.4, rated 21/32 city/highway.
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Old 12-04-2009, 09:13 PM   #27 (permalink)
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OK guys, I'm going to ask a REALLY dumb question, because I'm not an engineering type at all....

What is load? is that the amount of work the engine is under at a given RPM?
Ergo, load is higher at 2k rpm going up a hill than going down? Or is that a different concept?
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Old 12-09-2009, 05:19 PM   #28 (permalink)
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So there's no way to really know other than scangauge/mpguino? Are they 100% accurate on short term mpg?
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Old 12-09-2009, 05:35 PM   #29 (permalink)
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SG is pretty good over 2 miles. I do a number of 4 mile trips through downtown Columbia every week. It's pretty accurate, within half a mile per gallon.

Like all gauges, the SG is better up until your average tank length. I've had a 600-mile tank where it was 2 mpg off. It's accurate at 450 miles/tank, though.

If your car has a built-in instant or average MPG gauge, use that to see the results. The instant MPG gauge is by far the more useful for day-to-day use. The average MPG is good for comparing driving techniques across tanks.

Those 3.4's will easily get 33-34 highway if driven sensibly, and 25-26 combined. At least that's what the indifferently maintained 3.4 in my brother's GM minivan gets.
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Old 05-18-2011, 08:31 PM   #30 (permalink)
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Exclamation

Alright, I'm reviving this thread. I have been pondering this very same question for.... well, a long time.

It seems sometimes as though we drivers of automatics are shunned from the efficiency discussion. Unfortunately, my good ol' 3100 with the 4 spd is all I have for the time being and I have to make due with what I can get from it. Nevertheless, I see no reason not to at least TRY for better fuel economy, even if the transmission isn't the best tool for the job.

In order to settle this once and for all, I intend to employ various techniques of acceleration over the course of a long-distance trip, while monitoring certain parameters in Scangauge, to determine the method of acceleration that yields the least amount of fuel used.

I have tried monitoring AVG (average miles per gallon) before, with very broad results. I believe that either the TFC (trip fuel cost) or the trip total gallons consumed would be the best bet for this.

My idea is to record the starting cost or quantity at a stop. Then accelerate to 55 MPH and record the ending cost or quantity, repeating this for various acceleration techniques. Quite simply, the technique that yields the least fuel consumption from 0 to 55 MPH should be most efficient.

The techniques that I will test are:
  • Acceleration at a given throttle setting (10%, 20%, 80%, etc.)
  • Acceleration at a given MAP (manifold absolute pressure) setting (20 in. Hg, 22 in. Hg, 26 in. Hg, etc.)
  • Induced shifting at a given RPM (2000, 2500, 4000, etc.)

I'll be making the trip tomorrow. Not sure how many of these I'll be able to check out, but I will update when I get some results.

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