Optimal speed for the best MPG??? - Page 3 - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 01-22-2004, 11:05 PM   #21
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well i refill as soon as the chech gauges light comes on, i'm pretty sure i could squeeze more but ive ran out of gas twice in the past two months in my truck. i was being careless
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Old 01-23-2004, 12:10 AM   #22
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Quote:
Originally Posted by bonnie94sse
I drove with Cruise on at 50mph coming home from Canada, and on the yellow part of the fuel gauge alone, I got 90-100 miles out of it. I was surprised I made it home (I didn't have $$ for gas)
Spend it on too much beer?
For my Toronto trip the best mileage I got to was 35.7 to a gallon, I think. I was making stops around every half tank too.
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Old 01-23-2004, 09:23 AM   #23
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Keeping in mind that the question was at what speed you could get the best mileage and not could you get good mileage at speeds above 70, the horsepower it takes to overcome the resistance of the air goes up by the third power. So, if it takes x horsepower to overcome air resistance at 50mph, then it takes 70/50 x 70/50 x 70/50 hp =2.75x at 70.
Granted each engine has a point where it operates most efficiently but the aero factor is really the dominant factor. When the first gas crisis hit in the early 70s, everyone was asked to slow down to 55mph to conserve fuel. The Camaro I drove(which I still have) went from 17mpg at 70+ to 22mpg at 55.
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Old 01-23-2004, 11:12 AM   #24
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Quote:
Originally Posted by MarkFahey
For anyone with a DIC, you can pretty clearly see that all other things being equal, your best mileage is between 45-50 when the torque converter has locked up. Even with a SSEi, at that speed, the DIC on my car will read somewhere around 36mpg. Take it up to 70 and it drops to about the EPA rating of 27.
I did an experiment not long ago where I compared mileage at 70mph. I checked the mileage at 70 with no one around me and as stated above, I was getting about 27. Then I got behind a semi and drafted at 70 and was getting 33mpg.
Yeah, what he said.

I have pretty much come to the conclusion that about as slow as you can drive in OD with the torque converter locked up is about where you will get the best mileage in general for most cars. I know that is where I get my best mileage. My torque converter locks up when I am going ~43mph and crusing 45-50mph I get 42mpg according to my DIC on the freeway. (I found this out on a really snowy icy day when I had to drive slow) If I speed up to the normal 75mph I drive on the freeway, the DIC reads between 29 & 31mpg. Since my car has completely different gearing and aerodynamics than you, it may not be the same, but I still think that about as slow as you can go and be in OD with the TC locked up is going to get you the best mileage.

Shawn
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Old 01-23-2004, 08:35 PM   #25
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The best mileage I ever got was on a 250 mile round trip. I got about 24mpg or so. However, I would have gotten better but I had to go 125mi in 2 hours. So, I was going 110mph a lot and triple passing on two lane highways. On the way home I set the cruise at 70mph. During the ride home the guage moved the least. During the winter I can't seem to get more than 18mpg.
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Old 01-23-2004, 09:55 PM   #26
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im with dbtk2 on this one. The rule I have heard is for every 5mph faster you go, you lose 1 MPG. I have found this rule to be ~true. My thought is: less RPMs=less gas used...so you would get the most when it goes into OD (~45MPH). I think the next time I drive I'll set the cruise when the tranny shifts into OD and then use the decel to see how low I can go before it goes into 3rd. Ive read that 55MPH is the best compromise between speed and MPG.
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Old 01-23-2004, 11:29 PM   #27
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Quote:
Originally Posted by macho_mike21
Ive read that 55MPH is the best compromise between speed and MPG.
there is no set speed for best fuel efficiency, aerodynamics plays a large factor, and so does the gearing
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Old 01-24-2004, 01:02 AM   #28
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Quote:
I have pretty much come to the conclusion that about as slow as you can drive in OD with the torque converter locked up is about where you will get the best mileage in general for most cars. I know that is where I get my best mileage. My torque converter locks up when I am going ~43mph and crusing 45-50mph I get 42mpg according to my DIC on the freeway. (I found this out on a really snowy icy day when I had to drive slow) If I speed up to the normal 75mph I drive on the freeway, the DIC reads between 29 & 31mpg. Since my car has completely different gearing and aerodynamics than you, it may not be the same, but I still think that about as slow as you can go and be in OD with the TC locked up is going to get you the best mileage.
Yes I definitely agree. Shawn you are one bright guy!!
As low an rpm as you can go in as high a gear with the torque converter locked up. That will be a low enough speed ~45 mph that wind resistance won't come into play and tire resistance will be constant at any speed.
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Old 01-24-2004, 01:11 AM   #29
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Quote:
Originally Posted by MarkFahey
The Camaro I drove(which I still have) went from 17mpg at 70+ to 22mpg at 55.
A carburated engine is jetted to be the most efficient at 55mph.
I would say on our midsized (port fuel injection) cars it is the most efficient in last gear/OD with the torque converter locked up, and at its lowest revs.
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Old 01-24-2004, 01:08 PM   #30
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I think i get the best right around 50 MPH. i say this because at lower than 50 it'* only at around 1,200 RPM'* and it seems like you have to hold the gas down farther to keep that speed because of the RPM'* being so low. at 42 MPH it stays at around 950 RPM .
On the other hand, it'* easiest to keep 65 MPH. You barely have to have the gas down at all to keep 65 (1,600 RPM) so I'm really not sure! Wish I had a DIC to confirm. :(
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