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Old 11-01-2012, 04:57 PM   #1 (permalink)
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Smile Better MPG at 62MPH then at 55MPH

I have a 1999 Camry LE 4 Cyl 2.2 Automatic


I have an ultragauge hooked up and it has been calibrated

I have found that at just above 60MPH I get right round 40 to 42 mpg this is steady. On my way from Bakersfield to OC I got an average of 36 MPG on this trip. From what others have told me I should get better MPG at 55 but I don't isn't this strange?

Could it just be my car weight type of engine aerodynamics that cause right around 60 mph to be best speed for gas milage

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Old 11-01-2012, 05:15 PM   #2 (permalink)
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Its highly doubtful. There are too many variables to consider one trip's worth of data significant. There is wind, traffic, temperature just to name a few that can change your mileage a ton.
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Old 11-01-2012, 05:31 PM   #3 (permalink)
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The best way to test it would be A-B-A over the same stretch of road on the same day. Pick out a stretch of road (say 5-10 miles). Drive it both ways at 62 mph, then both ways at 55 mph, then both ways at 62 mph again. If desired, you can keep on repeating. The difference between the two 62 mph runs gives you an idea of the inherant variability in the testing, as well as whether things are changing over time.

If there actually is a real difference, I would suspect the auto tranny. You don't go through a shift between 55 mph & 62 mpg do you?

There's actually quite a few threads already on this topic. Increading FE with increasing speed is very rare:
http://ecomodder.com/forum/showthrea...u-15182-7.html
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Old 11-01-2012, 06:02 PM   #4 (permalink)
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I've driven several generations of Camry, and they all went into top gear at 45 mph.

Metro had similar results in the camry he tested:

http://ecomodder.com/forum/showthrea...2-a-23818.html


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Old 11-01-2012, 06:47 PM   #5 (permalink)
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broski499: full points for monitoring your trip MPG, but it's a case of apples & oranges.

There must have been different factors on each leg of the trip affecting the results - traffic, wind, elevation change, temperature etc.

If you graphed bi-directional runs (to cancel wind/grade effects) and with no other traffic around, you'd find that MPG at 55 MPH is going to be a little better than at 60.
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Old 11-01-2012, 07:12 PM   #6 (permalink)
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If this is your 'permanet' eco car, then you should do as Dave suggests.
Find a flat piece of land/freeway (should be easy in your neck of ca) and drive 10 miles up and 10 miles back using the gauge and cruise contrl.
Do 50, 55, 60,65 heck even 70.
Now you have a baseline for your car.

I always used the same strip of hiway (when I was in Sacrmento) to test my mods
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Old 11-02-2012, 07:44 AM   #7 (permalink)
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As others have said, many variables to consider...another is the engines output curve. As with many production cars, dyno graphs show power delivery is not always smooth with often dips / flat spots at certain rpms not to mention steep increases. Could be quite simply that the engine is at a more efficient power output rpm at 62 MPH cruise speed than at 55 MPH cruise speed. Since the speed difference is very small, this could be another answer to the question of why it is better at 7 MPH faster. A dyno of the car against speed might indeed show this. Probably the case for the other Camry results difference not being linear with speed increase.
I was bored and did a quick workout in excel based on aero drag alone, starting at 50 MPH and 10 HP required to maintain that speed right upto 100 MPH and the 80 HP (80.00003 as could not get it any closer than that) required to maintain that speed (as say just based on aero drag alone requiring 8 times the power to double the speed). So on my little mess about table I saw 12.31144 HP required to cruise at 50 MPH and 16.47182 HP for 62 MPH. So what if at that given rpm the engine is only producing 11 HP at 55 MPH and then a bit of a spike to 18 HP at 62 MPH. Just a thought. While aero drag can be plotted as it increases with the square of speed so you know exactly what it will be...engines outputs can not. While looking for that optimum run for best MPG, speed might have to be adjusted based on the specific engines power curve.

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Old 11-02-2012, 09:18 AM   #8 (permalink)
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DirtyTorquer, you're on to the root of this.

Work output of the powertrain necessarily increases with speed because the aero drag is increasing with the square on speed. So for your mpg to get better at higher speed, something about the powertrain operation has to change to allow you to produce more work that you were before with less fuel than you were before. I.e. if the higher speed means you need X% more work output, the powertrain needs to have become >X% more efficient. That scenario is possible, but pretty rare.
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Old 11-02-2012, 09:22 AM   #9 (permalink)
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Quote:
Originally Posted by broski499 View Post
I have an ultragauge hooked up and it has been calibrated
Can it display LOAD of the engine ?
See if there's much difference between the load at 55 and 60.

Quote:
I have found that at just above 60MPH I get right round 40 to 42 mpg this is steady. On my way from Bakersfield to OC I got an average of 36 MPG on this trip. From what others have told me I should get better MPG at 55 but I don't isn't this strange?
Try the different speeds repeatedly - for a full tank - so outside influences start to even out a bit.

If the car stays in the same gear, the lower speed should get better FE.
If it drops a gear, you can expect FE to suffer.
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Old 11-02-2012, 02:15 PM   #10 (permalink)
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And once upon a time I got 41 MPG out of a 1995 Dodge Neon at 80 MPH. But it was a warm summer day, I was moving with traffic in the fast lane, and a tail wind.

Wind has a huge effect. Most people cannot even feel a five MPH wind. But, at 60 MPH, that is the difference between 55 MPH and 65 MPH airspeed depending whether it's a tailwind or a headwind. The difference in aerodynamic drag is proportional to the square of the airspeed, or 40%.

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