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Old 06-29-2011, 11:11 AM   #11 (permalink)
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Being that you have a diesel (unthrottled), downshifting and lighter throttle doesn't hurt your efficiency as badly as a gas engine. Also, whether it's worthwhile to punch it, slow down, or downshift depends on how much power the engine has. If it can't hold speed at less than 80% throttle in top gear, you're probably better off slowing down.

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Old 06-29-2011, 01:49 PM   #12 (permalink)
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Driving my courier route last year through maryland and WV, my best mileage came from maintaining speed uphill (55~60) while keeping the engine in the highest gear. Then coasting downhill, keeping up with traffic as far as speeds, and continuing to coast until I was back to 55. I went from 33 to 36 mpg this way.
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Old 06-29-2011, 02:56 PM   #13 (permalink)
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Quote:
Originally Posted by brucey View Post
Driving my courier route last year through maryland and WV, my best mileage came from maintaining speed uphill (55~60) while keeping the engine in the highest gear. Then coasting downhill, keeping up with traffic as far as speeds, and continuing to coast until I was back to 55. I went from 33 to 36 mpg this way.
You were driving with load and then coasting in neutral. Did you use your ScanGauge to monitor engine load or just work it by feel? Sounds like the later. Works really well, huh?
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Old 06-29-2011, 04:17 PM   #14 (permalink)
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Both, had my scangauge, but got a feel for it. Having the stupid automatic made it extremely difficult sometimes to stay in 4th gear with the torque converter locked, but it was doable with some patience. Some of the coasts I had from the top of the hills were over 1.5 miles, probably would get even better mileage if I could have done EOC as well.
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Old 06-29-2011, 05:42 PM   #15 (permalink)
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Quote:
Originally Posted by Piwoslaw View Post
I crawl up hills at the slowest possible speed, often reducing both gear and speed instead of keeping gear and stepping on it, but I have no idea if this is the best way to do it since 95% of my driving is in flat-to-slightly-rolling terrain.
I think if you study the thread on BSFC-charts you'll see that with a diesel it's most likely best to just floor it.
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Old 06-29-2011, 06:05 PM   #16 (permalink)
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I pretty much agree with all that's been said. DCB's chart is key. Start at the bottom of the hill and apply 75% throttle and ~2000 rpm (in my experience it's slightly better than 2500). If that accelerates you up the hill, good. Cut power and coast near the top to crest the hill at the lowest reasonable speed. If it really accelerates you up the hill, split it into multiple p&g cycles. If you lose speed, downshift because you actually need the extra power. Next time try a faster approach at the bottom so you don't have to downshift.
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Old 06-29-2011, 09:02 PM   #17 (permalink)
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You want to reach your highest speed at the bottom of the hills. That speed should be in the range where you are not going to get a ticket or aggravate any other drivers.
In a Mustang GT you should have enough power to stay in highest gear at all times when you are applying power.

Basically the best way to understand the best tactic would be to think of it as a roller coaster, applying only enough power to overcome all losses and maintain your desired average speed. A squirt of high gear acceleration to get you to the top of the hill at the lowest speed tolerable to you and others, as long as you reach a reasonable terminal velocity at the bottom.

It really depends of the grade, distance between peaks, other traffic and speed limits in fine tuning your strategy, but you can achieve significantly better mileage than on level ground if you do it right, because you do not have to pulse and glide to higher speeds which exponentially increases your aero losses.

regards
Mech

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