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Old 09-06-2007, 09:50 AM   #21
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I think it's time to invoke Sagan:

Anyone claiming their common, modern car gets better fuel economy the faster they go is an exception to the rule. Extraordinary claims require extraordinary proof. Plot it, as above.

It just doesn't make sense in the case of the Skylark, Accord or CRX mentioned so far.
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Old 09-06-2007, 09:57 AM   #22
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My Accord's steady state fuel economy is much better over 60 than under 50 MPH.


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Originally Posted by MetroMPG View Post
Both in top gear? I find that difficult to believe.
Yes, 5th gear.

I found it hard to believe as well... I would have sworn 45mph/70kph would have been the sweet spot for the Accord. This was with rolling terrain mostly using CC going up past Barrie and Huntsville from the Toronto area on the long weekend. It was most likely a combination of 4 people in the car and the rolling hills. The engine seemed to be below it's sweet spot when driving at what would seem to be great FE speeds.

Best speed seemed to be 55mph, but going anywhere from 60 to 65 didn't seem to reduce mileage much. In comparison, dropping down to 50 really increased consumption on any upward pitches. I wish that ScanGauge had an altimeter and could graph stored data like my Polar hear rate monitor / bike computer!!! ;-)

If I ever take the Accord on the 401 west of London where the road is pretty well dead flat forever I'll report back the CC sweet spot.
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Old 09-06-2007, 10:04 AM   #23
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Could be... But not according to every singe BSFC map I've ever seen. I've never seen an engine geared properly that will increase efficiency by 30% if it's already near or greater than half load and minimal BSFC. Course, it could be that Honda designed a weird engine unlike any other engine, but if I had to pick between that and a lack of consistent testing on your behalf, I'm sure you can guess which one I'd pick.

I'm not sure why you are implying I have a lack of consistent testing. I only drive my CRX on my commute and drive my Integra on the weekends so for 99% of my driving, the car is driven on the exact same route, every day, same amount of hwy/city (I'm guessing about 70/30) driving. In my gas log below, arrow A is where I started using the same gas pump at the same station. From this point on, you can see that my mileage, though not wonderful for a CRX HF, is pretty consistent. From Arrow A to Arrow B I would try to shift below 2000rpm and keep the fwy speed below 65. From arrow B on, I'm shifting between 2500 and 3000rpm and the freeway speed between 75 and 80. Before I changed the speed shift points there's 1430 miles/32.88 gallons for an average of 43.46mpg and after I raised the speed there's 3588 miles/81.09 gallons for an average of 43.97mpg.

I have not changed anything in the car.

This is real world driving, averaged over sevaral hundred miles, unless you put the car on a test track with alot of instrumentation, I don't see how I'm going to get alot more consistent. To me, the numbers don't lie, I'm getting about the same mileage after increasing the speed.

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Old 09-06-2007, 10:37 AM   #24
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This was with rolling terrain mostly using CC ... 4 people in the car and the rolling hills.
Ah! CC. That changes everything. Particularly with the hills & added weight.

If you'd been using your foot & brain (if traffic had permitted), you would have greatly exceeded the CC's fuel consumption in those circumstances while maintaining the same average speed.

I can guarantee that on level roads at a constant speed your Accord gets better top gear fuel economy at 50 mph vs 60+, and better still at 40.
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Old 09-06-2007, 10:55 AM   #25
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This is real world driving, averaged over sevaral hundred miles, unless you put the car on a test track with alot of instrumentation, I don't see how I'm going to get alot more consistent. To me, the numbers don't lie, I'm getting about the same mileage after increasing the speed.
You need a SG or SM, a deserted section of road, a bunch fo runs, and consistent weather to do an accurate comparison. Traffic alone can screw with a test in a ton of ways, not to mention any changes in weather, fill ups, etc... If you're trying to compare tanks while commuting it's nearly unpossible to do so in an accurate matter. Especially if you're a typical CA driver...
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I think if i could get that type of FE i would have no problem driving a dildo shaped car.
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Old 09-06-2007, 11:15 AM   #26
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Quote:
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You need a SG or SM, a deserted section of road, a bunch fo runs, and consistent weather to do an accurate comparison. Traffic alone can screw with a test in a ton of ways, not to mention any changes in weather, fill ups, etc... If you're trying to compare tanks while commuting it's nearly unpossible to do so in an accurate matter. Especially if you're a typical CA driver...
I would would agree with you on one or two gas tanks, but I think I have enough miles at each speed to average out the weather/fillups/traffic etc to show if the mileage were worse at the higher speeds I would see it.
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Old 09-06-2007, 11:26 AM   #27
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Not unless you can control for average speed, time idling, acceleration, energy lost via braking, etc... accurately. Ime on busy CA freeways, traffic will clump in groups and tunnel, except for commercial stuff. There is no hope of getting a controlled comparison from that mess, ever. Imo of course...
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I think if i could get that type of FE i would have no problem driving a dildo shaped car.
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Old 09-06-2007, 12:19 PM   #28
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(A) Ah! CC. That changes everything. Particularly with the hills & added weight.

(B) If you'd been using your foot & brain (if traffic had permitted), you would have greatly exceeded the CC's fuel consumption in those circumstances while maintaining the same average speed.

(C) I can guarantee that on level roads at a constant speed your Accord gets better top gear fuel economy at 50 mph vs 60+, and better still at 40.
(A) What added weight? We actually had an empty seat! You sound single... LOL

(B) My legs are cramped in the Accord - CC is my survival tool, so I'm very much guilty of trying to keep my feet out of it.

My brain however was very much FE engaged, much to the chagrin of my wife who was very relieved after the long weekend when "she" removed my ScanGauge from her car!

I had fun trying to find the sweet spot for CC in mildly rolling terrain. I was testing raw cruise and also assisted cruise (tap speed back on climbs). Tapping back had minimal impact when the approach speeds were near 50 or lower - unless it was a very small rise. Getting back to speed after seemed thirstier until it got closer to its sweet spot.

(C) I totally agree, but terrain and traffic are facts of life in most driving scenarios. Like I said, if I get the chance to ever test it on flatter terrain, I'd like to know what the optimum steady state speed is on flat stuff. Too bad that it won't be the Accord going to Florida in December... I can't believe I said that!!! ;-)
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Old 09-06-2007, 12:37 PM   #29
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(A) Guilty!

(B) You've got to do what you've got to do. Glad to see you're at least playing with DWL somewhat through the CC controls. I've done that a bit, but my experience is cruise can be brutally abrupt, and hard to tame that way.

Anyhoo, a waaay different picture has emerged with the added context you've given that was missing from the simple statement "My Accord's steady state fuel economy is much better over 60 than under 50 MPH."
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Old 09-06-2007, 12:49 PM   #30
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were you driving in a pack of cars? If you are going 75-80mph with a bunch of other cars, and you're all driving close to one another--that is, a long tailgating train of drafting, you will get much better FE than if you are driving 75-80 without any cars around. You mentioned slingshotting from 18wheelers - obviously drafting behind these is good FE.

A 4cylinder engine, even on a buick, should not be more efficient at speeds above 65mph. my guess the "culprit" is tail wind and/or pack driving.
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