Best way to drive hills
 

Heres the situation, a road with hill after hill. Whats the best way to traverse it with the least amount of fuel?

I can only imagine several ways:
EOC from the top of the 1st hill then go slow in a high gear up the next.

Speed up down the 1st hill and then coast up the next hill.

Speed up half way down the 1st hill then EOC half way down and half way up the 2nd hill then low speed up the rest of the 2nd hill.

When driving something ridiculously overpowered you definitely want to EOC downhill and accelerate uphill. If the inclines are too long, or not steep enough, you may split them up to more than one pulse.

Power up the hill, but cut power at the right time to crest the hill at a relatively slow speed. Engine off coast until your speed reaches your slowest desirable speed in the highest gear. Bump start and accelerate up hill if possible, or run at economical cruising speed to the next hill. You could also eoc pulse and glide to the next hill. Always try to crest the hills at a relatively slow speed, especially if you don't know what is on the other side of the hill (a stop sign at the bottom?).

Light acceleration downhill to pick up speed, then gradually back off the throttle after you start climbing - still letting off as you go up, [steady throttle if you have a longer climb, but not accelerating], coast over the top, then gradual acceleration on the downhill, repeat.

It takes less horsepower and fuel to accelerate on the downhills than it does to try to power up the next hill. You may have to do some testing to see what works for you. I'd skip the EOCing if you have lots of ups and downs to do.

I'm using my ultra gauge to drive with 70-80% engine load going up hills. Your car, with its power, would possibly fly at 80% load. But you want more load--within reason--for more efficient use of engine movement/power... That's my understanding and practice.

99Metro: ive seen semi trucks use that method. Almost like they are keeping close to the same engine load instead of maintaining the same speed.

California98Civic: It idles at 11% load and 20-25% load can move it pretty well. Maybe 35%ish for a big long hill.

In higher powered, overgeared vehicles, powering up the hill is better, as it keeps the engine closer to its sweet-spot. In the case of my Jeep, I get my best highway mpg by maintaining steady speed up a hill, and then coasting down the backside, provided it's not steep enough for me to gain speed on the descent.

The mpg achieved from that is certainly better than what I see on flat ground, or very long, steep hills (where slowing down at the top doesn't prevent me from getting above my cruise speed by the bottom).

I agree with most of the others. Accelerate up the hill, coast down it.

The ultimate hill approach IMHO, ignoring minimum speed concerns for a moment, is to use the extra load on the climb to get to the best bsfc spot. i.e. find the best compromise between 75% load and 2500rpm if your bsfc map looks like the following (manual trans assumed). And then kill the engine near the top of the climb so that you barely coast over the top and down the other side.

http://ecomodder.com/wiki/images/3/3..._dohc_bsfc.jpg

Note, efficiency tapers off more gradually to the "west" or the "southwest", so that is the side I would error on if possible.

Couldn't someone just do a more or less reasonable A-B-A-B test of different hill climbing methods? Someone who commutes in hilly territory could try one method on even days, another on odd days, and average it out after 2-3 months.

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.

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.

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?

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.

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.

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.

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