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Old 05-12-2009, 10:03 AM   #1 (permalink)
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Slowed down - picked up 2+ mpg!!!

I slowed from my usual 9 over the speed limit cruise to a 1 over the speed limit cruise. I didn't get a rash, so I'll keep doing it. My method was still 9 over the speed limit up to 45 mph (34 in a 25, 44 in a 35 etc). At 45, I change to 1 over, which keeps my average speed up into a more efficient range, without the larger drag from speeds over 45. This didn't work in my Mustang, but it did in the new ride...

I hypothesize that the larger engine in the Mustang was not affected by the relatively small differences in drag. At cruise rpms, the motor probably had more than enough torque to push the car, so variances between 55 and 70 had little to no effect, since long cruises never generated significant changes in FE.

In a larger (wetted area) car with a smaller engine, such as the Fusion, the difference is greater.

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Old 05-12-2009, 10:45 AM   #2 (permalink)
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Compare the Cd and frontal area of the Mustang and Fusion.
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Old 05-12-2009, 12:15 PM   #3 (permalink)
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Quote:
Originally Posted by Bullockracing View Post
I slowed from my usual 9 over the speed limit cruise to a 1 over the speed limit cruise. I didn't get a rash, so I'll keep doing it. My method was still 9 over the speed limit up to 45 mph (34 in a 25, 44 in a 35 etc). At 45, I change to 1 over, which keeps my average speed up into a more efficient range, without the larger drag from speeds over 45. This didn't work in my Mustang, but it did in the new ride...

I hypothesize that the larger engine in the Mustang was not affected by the relatively small differences in drag. At cruise rpms, the motor probably had more than enough torque to push the car, so variances between 55 and 70 had little to no effect, since long cruises never generated significant changes in FE.

In a larger (wetted area) car with a smaller engine, such as the Fusion, the difference is greater.
Try doing the speed limit everywhere, you will probably pick up more MPG's especially with that gas sucking V8. Keep in mind, the slower the engine turns, the less fuel it uses. So as long as you are in the high gear you'll save gas at slower speeds, provided you aren't lugging the engine.
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Old 05-12-2009, 02:44 PM   #4 (permalink)
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Old 05-13-2009, 01:42 PM   #5 (permalink)
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Quote:
Originally Posted by binarycortex View Post
Try doing the speed limit everywhere, you will probably pick up more MPG's especially with that gas sucking V8. Keep in mind, the slower the engine turns, the less fuel it uses. So as long as you are in the high gear you'll save gas at slower speeds, provided you aren't lugging the engine.

Yeah, the gas-sucking V8 [car] is gone. The Mustang didn't have any onboard mileage devices, but I know it did very poorly at low speeds. Anything over 35 mph was a cruise in fifth gear. I think the motoring horsepower required just to turn the motor at whatever speed was in excess of the required amount to move the car. I did measure (A-B-A comparison) that the Mustang got the same mileage at 55 as it did at 70.

The Fusion is an automatic, and it won't go into top gear below 45 or so, since the throttle load will keep the transmission in a lower gear, or at least out of lockup (not sure which) above 45 or so she gets very happy at low rpms.
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Old 06-05-2009, 06:39 AM   #6 (permalink)
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Quote:
Originally Posted by Bullockracing View Post
Yeah, the gas-sucking V8 [car] is gone. The Mustang didn't have any onboard mileage devices, but I know it did very poorly at low speeds. Anything over 35 mph was a cruise in fifth gear. I think the motoring horsepower required just to turn the motor at whatever speed was in excess of the required amount to move the car. I did measure (A-B-A comparison) that the Mustang got the same mileage at 55 as it did at 70.

The Fusion is an automatic, and it won't go into top gear below 45 or so, since the throttle load will keep the transmission in a lower gear, or at least out of lockup (not sure which) above 45 or so she gets very happy at low rpms.
That you got the same mileage at 55 and 70 makes 0 sense to me. At 70 your fuel consumption should have dropped like a rock. At 70 you should be experiencing a LOT more wind resistance.
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Old 06-05-2009, 09:12 AM   #7 (permalink)
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I keep reading people saying that as well: claims of better/same MPG with big V8's at moderate vs. higher speeds, and I'm skeptical too. Sounds like wishful thinking or maybe selective "data" by folks who like to drive fast. Maybe it's true, but I'm skeptical. (My only V8 was my first car, over half a lifetime ago!)

Just had a thought: I know a guy with a Corvette ZR1 (I think). I'm going to ask if he'd be interested in plotting a speed vs. mpg graph for it.
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Old 06-05-2009, 11:03 AM   #8 (permalink)
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Quote:
Originally Posted by MetroMPG View Post
I keep reading people saying that as well: claims of better/same MPG with big V8's at moderate vs. higher speeds, and I'm skeptical too. Sounds like wishful thinking or maybe selective "data" by folks who like to drive fast. Maybe it's true, but I'm skeptical. (My only V8 was my first car, over half a lifetime ago!)

Just had a thought: I know a guy with a Corvette ZR1 (I think). I'm going to ask if he'd be interested in plotting a speed vs. mpg graph for it.
Ok, I was worried that it was just me! I'd be interested to see that data. Is it possible that the static draw is so large that it bumps up the optimal fuel efficient speed that much??

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