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Old 12-10-2009, 01:30 PM   #1 (permalink)
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Hills (most efficient climbing technique for diesel / manual transmission?)

Simple question - what is the best way to deal with hills or inclines ? Do I burst up them quickly in one go or take it slowly at lower MPG ?

(Obviously I'm tapping about going up and not down)

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Old 12-10-2009, 01:39 PM   #2 (permalink)
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I usually find myself pulsing up hills just to keep speed up. To be honest, I don't think it matters with a manual transmission. With an auto, you just want to avoid real hard acceleration.
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Old 12-10-2009, 06:39 PM   #3 (permalink)
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Depends on the hill. Short ones I usually pulse. Long ones I grind up. It depends on your car. Darn slushbox.
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Old 12-10-2009, 09:43 PM   #4 (permalink)
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For most cars, as long as you can hold top gear, constant speed is fine. One step better would be full throttle acceleration in top gear on the way up the hill, and engine off coasting on the way down.
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Old 12-10-2009, 09:49 PM   #5 (permalink)
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Living in WV I've watched my scangauge a lot. The best way I've found (automatic transmission) is to have speed when you start the hill and bleed it off a bit as you climb the hill. Letting go of the gas completely JUST before the peak and coasting all the way back down.

This method is almost as good as a level straight.

In fact, I might go do a few scangauge tests right now and report back.
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Old 12-11-2009, 05:26 AM   #6 (permalink)
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Interesting. My car is manual and diesel. I'm experimenting between pulsing and grinding (nise phrase ) and also which gear to use. Higher gear, lower RPM means I sometimes have to prod harder to maintain speed and as the Diesel is fuel controlled that means more fuel going in. But a lower gear means higher engine speed, less fuel but more cycles.

Pulsing is harder as the roads here are very heavy on traffic, and there is usually some muppet in a van about an inch or so off my rear end.

I shall have to practice technique more to maintain momentum

Thanks guys.
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Old 12-11-2009, 08:13 AM   #7 (permalink)
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Since you have a manual I believe the most efficient way to go up a hill is in top gear at the lowest rpm that will allow you to remain in top gear without lugging (I define lugging as a condition when you can't accelerate without downshifting).
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Old 12-11-2009, 08:43 AM   #8 (permalink)
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Quote:
Originally Posted by Arragonis View Post
Interesting. My car is manual and diesel. I'm experimenting between pulsing and grinding (nise phrase ) and also which gear to use. Higher gear, lower RPM means I sometimes have to prod harder to maintain speed and as the Diesel is fuel controlled that means more fuel going in. But a lower gear means higher engine speed, less fuel but more cycles.

Pulsing is harder as the roads here are very heavy on traffic, and there is usually some muppet in a van about an inch or so off my rear end.

I shall have to practice technique more to maintain momentum

Thanks guys.
In heavy traffic where close proximity is unavoidable, use drafting to improve your mileage.

"Lugging" an engine refers to the old carbureted gasoline engines where if you gave it more gas pedal the accelerator pump would squirt a given amount of fuel to the engine. This would be too much fuel for low RPM and high load, which is not good for power or emissions.

A modern Diesel or Gas engine can not really suffer from "Lugging" in the classical sense, because the fuel delivery is precise, regardless of the load.
In order to lug a modern engine you would have to go very low in the RPM range, down below 1100, give or take, depending on the engine being a performance type or an economy type.

I agree with downshifting if you have to apply full throttle in the higher gear to maintain your speed. Actually it depends on your RPM and your BSFC map for your specific engine. A good general speed would be 2000 RPM for almost any engine that was designed for economy. If you drop below that point in your climbing phase, then downshifting would probably give you better mileage.

A Diesel is different in this aspect from a gasoline engine since it has no manifold vacuum, but even with no manifold vacuum, lower RPM will be more efficient as long as you do not go below about 1500 when climbing hills. Even with that said, it still depends on the size of you engine in relation to your vehicles gross weight. Higher power to weight lower RPM and vice versa.

It's not a "written in stone" tactic and can change somewhat even based on the number of passengers in your car, but with a Diesel as long as you stay in the general area of best BSFC you will get best mileage as long as you use the least average RPM it takes to do the job.

regards
Gary
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Old 12-11-2009, 09:40 AM   #9 (permalink)
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I live in a small hilly area of NC so have this on my daily commute. Lots of traffic here so I need to be somewhere around the psl while driving. For steep up hills I find the speed required at the bottom so I can bleed speed until I reach the top. One hill, on a 55 psl 2-lane road, I need to be at 62 mph at the bottom and I will be at 52 mph at the top. If no one is behind me I can FAS at the top, at 52 mph, and glide along slowly losing speed until I need to restart and accelerate. If being followed I can maintain that 52 mph getting around 80 impg until I reach the down hill. I use the impg (instantaneous miles per gallon) gauge on the SGII to adjust throttle. 25 impg while around 55 mph is a pretty standard power climb number for me. Long highway up hills it is just grinding it out taking whatever mileage I get. I try for 30+ impg on these. This enables me to maintain 55 mph usually.

Short steep hills basically same technique, I just need to adjust the initial speed. In the rollercoaster areas (lots of smaller ups and downs) where the hills are fairly close together I use a pulse and DWL. Pulsing on the downhill and DWL on the uphill. I found that trying to accelerate going uphill is a losing battle; I use more gas than I can gain by gliding down the other side. I don’t gain as much by accelerating going down but I also lose much less while going up. In traffic this also lets me maintain a more constant speed and seems to help prevent major tailgating. If no one is behind me I can throw a few FAS’ in and coast up and down a few before losing too much speed and having to restart.
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Old 12-13-2009, 05:50 PM   #10 (permalink)
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Quote:
Originally Posted by Old Mechanic View Post
In heavy traffic where close proximity is unavoidable, use drafting to improve your mileage.
I appreciate the rest of the information but can't agree with this part. I like to have space in front for the unexpected.

In fact I think drafting is unsafe.

When I used to drive an Mini (as in old style economy car designed by my namesake as opposed to a MINI designed by a marketeer in Frankfurt) I used to slipstream a lot. It worked. The air vents would go quiet when I got into the "tow" and I would gain a magic 3-5 mph.

Driving in SC during my first time in the US with my girlfriend a few years ago, we passed a junction (on-ramp) and a van decided to swap lanes with no matching speed in front of the guy in front of me. Despite him braking hard I allowed the gap to close a lot, slowing more gently.

In the meantime my girlfriend was screaming "stop now, stop now".

I shouted "look behind".

All you could see in the rear view was a huge, white grill with the letters K C A M across the front (it was in my mirror) swaying from side to side as the moron in the logging truck behind struggled to stop his trailer with locked brakes from fish-tailing and wiping out the other three lanes.

My 100 yds of space meant I could slow gently and avoid being the hire-car-POS-Altima filling in a truck/SUV sandwich.

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