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Arragonis 12-10-2009 12:30 PM

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)

Daox 12-10-2009 12:39 PM

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.

99LeCouch 12-10-2009 05:39 PM

Depends on the hill. Short ones I usually pulse. Long ones I grind up. It depends on your car. Darn slushbox.

RobertSmalls 12-10-2009 08:43 PM

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.

brucey 12-10-2009 08:49 PM

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.

Arragonis 12-11-2009 04:26 AM

Interesting. My car is manual and diesel. I'm experimenting between pulsing and grinding (nise phrase :thumbup:) 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.

tasdrouille 12-11-2009 07:13 AM

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).

user removed 12-11-2009 07:43 AM

Quote:

Originally Posted by Arragonis (Post 146671)
Interesting. My car is manual and diesel. I'm experimenting between pulsing and grinding (nise phrase :thumbup:) 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

WoodyWoodchuck 12-11-2009 08:40 AM

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.

Arragonis 12-13-2009 04:50 PM

Quote:

Originally Posted by Old Mechanic (Post 146701)
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.

SentraSE-R 12-13-2009 06:10 PM

Like many of the others, I find bleeding off speed while climbing shorter hills is best. I've gotten 37 mpg with my SE-R on a 3 mile drive with a cold engine, by climbing a hill the first mile, and coasting the next two miles.

On long hills, there's no way around slogging it all the way, in the highest gear that will maintain speed. I typically get only 15-25 mpg climbing those hills, but FASing down them usually brings my mileage back to normal.

The Atomic Ass 12-15-2009 08:43 AM

Quote:

Originally Posted by Old Mechanic (Post 146701)
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 have never heard lugging as being ascribed to carburetors, I've been told that lugging is the detonation you get under high load at low RPM, which for a 4-cyl can be as high as 1,500, and in the case of my Ninja, 2,500.

WoodyWoodchuck 12-15-2009 02:13 PM

I forgot to add one technique I use. There is one small hill, maybe 50’ to 75’ elevation right after a narrow 2 lane bridge on a back road. After the initial steep part it slowly gains elevation for about 0.4 of a mile. I have found that powering up the initial steep section to gain speed to 50 mph (psl 45 mph) will net me greater overall mileage (read: less of a loss) than gliding to the base and DWL up the entire section at 45 mph. I’m assuming it has to do with my engine BSFC chart and finding the right rpm/mph combination for the climb. Unfortunately this is the only section of my commute that I have found this technique works on.

Bottom line, try different ways of approaching hills and see if there is a combination of rpm/mph/gear that works best.

Arragonis 12-15-2009 03:03 PM

OK, you got me. Whats a "engine BSFC chart" when its at home ? :confused:

user removed 12-15-2009 03:48 PM

BSFC stands for Brake Specific Fuel Consumption.

Its a graph of the best areas of power and RPM based on the most horsepower for the least fuel consumed per HP.

regaards
Mech

dcb 12-15-2009 04:08 PM

Not sure about the OP diesel, but hills in mine should be gone up at 1750 rpm and full throttle in the highest gear that will get me closest to that, followed by an unobstructed glide on the backend of course :) But that is where I make the most power for a given amount of fuel on my tdi. Start gliding prior to the peak so that you glide crawl over the top and reduce need for braking as appropriate.
from ecomodders very own wiki (which anyone can edit/contribute to) Brake Specific Fuel Consumption (BSFC) Maps - EcoModder
http://ecomodder.com/wiki/images/8/8....5-03_bsfc.jpg

Arragonis 12-15-2009 04:12 PM

Is there a temple where one may make offerings or incantations to obtain said chart ?

Or indeed a website ?


EDIT : Ahh, I see.

user removed 12-15-2009 04:19 PM

Quote:

Originally Posted by The Atomic Ass (Post 147822)
I have never heard lugging as being ascribed to carburetors, I've been told that lugging is the detonation you get under high load at low RPM, which for a 4-cyl can be as high as 1,500, and in the case of my Ninja, 2,500.

The carburetor in your Nnja (correct me if I am wrong) is very similar to the original SU types used in Britain dating back to the mid century.

They are a variable venturi type without accelerator pumps. A single tapered needle and seat with a ported vacuum operated diaphragm (either rubber or metal) raises the needle and changes the volume of fuel in relation to throttle opening and engine speed.

Without any accelerator pump you do not have the issue of a specific volume of fuel being introduced into the engine regardless of the engine's speed.

In the classic term, the way I learned it in the 1960S, lugging an engine meant you were engaging the accelerator pump at too low RPM. The amount of fuel entering the engine was far too much for the volume of air. This made the mixture so rich, most of the fuel was not mixed properly for combustion.

Lugging a Ninja would certainly occur at higher RPM, when you consider the redline of the 250 CC engine, which (again if memory serves me right) is in the 12-14k RPM range. Some Bike engines are even higher.

Now I would not consider that a typical passenger car engine, especially if we are discussing a diesel, many of which would never operate at RPM ranges much higher than 2500. At 12k, I am not aware of any diesel that would not have disintegrated long before that RPM level was reached.

My VX shift indicator lights up to recommend an up shift at 1000 Rpm in 5th gear. That's a very low RPM level for 5th gear operation, but in the VX the engine is designed for that low speed torque.

To the original poster;

When I recommend drafting in heavy traffic, it is always in the right lane. The Interstates here have very heavy traffic volumes. One section here has 49,000 cars pass over the same spot, in the same lane, every day.

When you divide 84,600 seconds per day by 49,000 vehicles, you have less than 2 seconds of average separation per vehicle 24-7. Understand that during the 10PM to 6 AM hours the traffic volume is much lower on average, the separation time during heavies flow is less than 2 seconds per car, probably less than 1.5 seconds. At 55 MPH PSL, that amounts to an average separation distance of about 110 feet minus the vehicle length average of 15 feet. 95 feet separation distance average for 18 hours a day, including tractor trailers and other large vehicles.

My drafting distance is the same as my stopping distance in those conditions. Even then, you will have people cut in front of you and pass on the right, the vehicle in the left lane. Some separation distances and so ridiculously low, I can read the month and year on the license plate stickers in my rear view mirror, and my eyes are not that good any more.

If you leave more distance between you and the vehicle in front of you and the vehicle behind you is inches from your rear end (as you previously stated), is the danger not greater than if the distances were more close to the same?

The last 5 plus times I have been involved in any collision, I was hit in the rear, so that is where the danger is greatest, at least for me in my particular circumstances.

Driving for 44 years.

regards
Mech

user removed 12-15-2009 04:23 PM

Traffic Cameras | HamptonRoads.com | PilotOnline.com

Check out the bridge tunnel section at normal rush hours for bumper to bumper traffic.

regards
Mech

dcb 12-15-2009 04:25 PM

Quote:

Originally Posted by Arragonis (Post 147922)
Is there a temple where one may make offerings or incantations to obtain said chart ?

Or indeed a website ?


EDIT : Ahh, I see.

LOL, did my post make any sense?

Arragonis 12-15-2009 05:10 PM

Quote:

Originally Posted by dcb (Post 147928)
LOL, did my post make any sense?

Yeah, sort of. ;) In between my original post and the edit is when yours appeared. I need to tap faster.

I see the graph. Mine is the ASZ version of that engine (130hp) but probably similar. Not sure about the full throttle thing though as that would surely just mean unburnt excess fuel (Diesel = fuel controlled) and in any case the turbo would kick in and I would be at 2500+ before I know it.

I shall experiment with the highest gear approach though, part throttle enough to maintain speed or bleed it off enough to get to the top and then coast down. I don't EOC as my steering and brakes don't work well with no engine.

EDIT : Reason for my post is I'm kind of living of the instant MPG reading and its painful watching it hit 25 or less when going uphill vs --- (i.e. infinity) when going down.

dcb 12-15-2009 05:15 PM

there is less return on EOC for a diesel, but clutch/neutral coast will carry you farther than coasting in gear.

I don't have reason to believe full throttle on a small smart diesel = proportionately more unburnt fuel, otherwise my bsfc peak would not be sitting on the torque curve.

Christ 12-15-2009 05:32 PM

As I learned it, lugging is defined as the point in the engine's power curve where it doesn't make enough power at full throttle to maintain your current vehicle speed. This would make the lug-point dynamic, not static.

I follow this rule, except at 80% throttle in gassers. (Unless they're GDI, then 100% is OK.)

I've never heard the definition regarding the use of carbs at all, and I find it unlikely, since diesels also suffer from lugging issues.

Peter7307 12-15-2009 06:52 PM

Quote:

Originally Posted by brucey (Post 146557)
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.


Yep this is the same technique I use as well but I think the hills here are not as frequent or steep as those in West Virginia.

A "get momentum working for you" approach is the best option if the hill allows it but where it is along haul then drop into a lower gear earlier and maintain as much as you can.

Pete.

Dieselman 12-16-2009 11:23 AM

Quote:

Originally Posted by dcb (Post 147921)
But that is where I make the most power for a given amount of fuel on my tdi. Start gliding prior to the peak so that you glide crawl over the top and reduce need for braking as appropriate.
from ecomodders very own wiki (which anyone can edit/contribute to) Brake Specific Fuel Consumption (BSFC) Maps - EcoModder
http://ecomodder.com/wiki/images/8/8....5-03_bsfc.jpg

I can believe that chart to be accurate for the VW 130Bhp engine. We too have a Skoda Vrs and I can feel the engine become more torquey and efficient in the range of 1,500-2,500 rpm. This is borne out by the instantanoius mpg reading climbing rapidly once 1,500 rpm is breached.

A standard rule of thumb used to be drive within the range of peak torque +1000rpm -500rpm for best efficiency. Under light load lower revs can be used without the engine bogging down. I'd be wary of running high loads at low revs in a diesel as that can create very high forces on the big ends and crank.

For hills I use the 'arrive a bit quicker and let speed bleed off slowly' technique.
In the Vrs one needs to be careful to not be in too high a gear under load, it seems to increase consumption.

Arragonis 12-17-2009 03:07 AM

One other issue doing this in the UK is traffic volume, quite often people just don't like following someone driving with load or doing the rollercoaster. In my view they should just leave a long gap (I do this to break up jams often) but I'm usually in a minority.

I shall experiment further, there are plenty of hills to try.:turtle:

user removed 12-17-2009 08:35 AM

Quote:

Originally Posted by Arragonis (Post 148318)
One other issue doing this in the UK is traffic volume, quite often people just don't like following someone driving with load or doing the rollercoaster. In my view they should just leave a long gap (I do this to break up jams often) but I'm usually in a minority.

I shall experiment further, there are plenty of hills to try.:turtle:

The roller coaster is most efficient for the professional driver who makes a living hauling loads. Reducing fuel cost means money in their pocket.

On I95 between Richmond and Washington DC, the truckers will do the "roller coaster" with speeds ranging from 53 to 75 MPH in a 65 zone. Leaving stopping distance (3 stripes x 43 feet) between us is my favorite position on that road in heavy traffic. The road is 3 lanes each way, and if you get in the inner two lanes the aggressive drivers treat it like a NASCAR race, with separation distances measured in feet and passing proximity measured with a yardstick.

Instead of trying to impose my desire for better driving habits on others, I just pace myself behind the trucks, which generally stay in the right lane.
This also gives me an escape route to the right, where the shoulder is paved and as wide as either of the three lanes available for traffic.

The hills around Fredericksburg are of sufficient grade to allow coasting (in neutral-engine on) at speeds of 70+, and in some cases you even need to use DFCO to keep your speed down. While you may see only 25 MPG on the uphill section, on the same hill's downhill section the mileage can exceed 300 MPG.

Doing this achieved the highest single trip mileage I ever recorded in my VX, over 68 MPG, at an average speed on 64 MPH. May of 2008 when fuel cost here were approaching $4 per gallon. Two passengers and cargo with a total weight of about 500 pounds.

I prefer alternative routes to the above mentioned scenario, but at night, the greatest danger here is Deer running out in front of your car. A friend once hit a Deer and it came through the windshield of his van. They had to open the door to let the Deer out.

regards
Mech

Arragonis 12-17-2009 05:45 PM

I agree - except being in Scotland most roads are 2 lanes only - so nowhere to hide and not be annoying.

dcb 12-17-2009 06:40 PM

ok, well in answer to the original question (and the title of this thread), it is as I described, load up the hill at bsfc peak and glide down and glide crawl over the top so you brake less.

Maybe we should change the thread title to "Hills (most efficient climbing technique for diesel / manual transmission after I put a whole bunch of conditions on it)" :)

Arragonis 12-18-2009 03:03 AM

Does it make a difference if I'm wearing glasses ? :D

Burnt 12-18-2009 09:52 AM

Quote:

Originally Posted by dcb (Post 148440)
ok, well in answer to the original question (and the title of this thread), it is as I described, load up the hill at bsfc peak and glide down and glide crawl over the top so you brake less.

Maybe we should change the thread title to "Hills (most efficient climbing technique for diesel / manual transmission after I put a whole bunch of conditions on it)" :)

Could one of you who knows what you're talking about maybe enter a little more about what BSFC is onto the ecomodder wiki entry, for us that don't have a clue about physics/mechanics?

This sounds like a pretty important concept to learn


edit: never mind, i just looked at wikipedia
edit again: just read the article, have not a clue what it means
edit #3: great article here

user removed 12-18-2009 03:22 PM

Actually I look at it differently. Here is my example.

Take an engine that has no throttle plate and produces 20 horsepower (under load) at sea level, then move it to a higher altitude.

As the atmospheric pressure becomes lower the power developed becomes lower, regardless of the fact that there is no throttle plate.

At a certain altitude depending on the mechanical compression of the engine, the atmospheric pressure becomes so low that there is not enough compression for combustion to occur.

You control the power developed by gasoline engines by restricting the atmospheric pressure. The pressure available for compression, in the cylinders, is the difference between the atmospheric pressure and the manifold vacuum.

Diesel engines are different, because they will run with very lean mixtures, compared to throttled gasoline engines, which require a specific range of air-fuel ratios to run properly.

Regardless of whether the engine is gasoline or diesel, the power developed is directly proportional to the available air pressure that enters the cylinders to be compressed and ignited.

I call this effective compression.

BSFC is (at 2000 RPM typically) a direct relationship with effective compression. The higher the effective compression the more efficient the engine. Supercharging increases effective compression by increasing the available pressure beyond atmospheric.

Without supercharging aircraft engines lose power at altitude, supercharging restores lost effective compression at altitude.

It's not so much the energy required to pull air past a throttle plate that creates inefficiency as it is the lower compression available due to throttle restriction.

I used the diesel example to illustrate the point about atmospheric pressure reduction creating lower available power at the same RPM.

regards
Mech

Arragonis 12-18-2009 03:38 PM

Diesels have no throttle as they are fuel controlled - more fuel, more powah.

They need compression to ignite the fuel - higher compression means air heats up to super temps and fuel ignites as it is injected.

In older engines the injection took place in one go from a mechanical pump. In more modern engines injection takes place over lots of phases - a little bit at the start to heat things up, the power bit (depending on pedal position, engine speed etc.), and then a little bit later on to deal with anything left over - to reduce emissions.

The timing and volume of these depends, as I tapped and as I understand it, on loads of variables (the map) - engine temp, engine speed, pedal position, turbo boost, fuel quality, zodiac position - all sorts.

But I think lugging is basically when the engine makes less on the power stroke than is needed to maintain rotation speed.

Maybe I have this wrong.

CoastRider 12-19-2009 12:20 AM

I lug my gasser I6 down to 800 rpms basicly idleing, in 5th gear 25-30 mph and its happy as long as its flat. I can maintain 15 in of vac and pull in 30+ mpg (mpguino)

The Atomic Ass 12-19-2009 06:59 PM

Quote:

Originally Posted by Christ (Post 147945)
As I learned it, lugging is defined as the point in the engine's power curve where it doesn't make enough power at full throttle to maintain your current vehicle speed. This would make the lug-point dynamic, not static.

My father's truck "lugs", (audible detonation, timing is almost entirely cut out by the computer), if I give it too much throttle at too low an RPM. Even if it does still accelerate. This generally happens at <2K, above that it does not happen under any conditions. I've held the throttle to the floor in top gear, with the engine spinning around 3K, and it would not accelerate further due to the grade, but it was not lugging.

The Atomic Ass 12-19-2009 07:15 PM

Quote:

Originally Posted by Arragonis (Post 148669)
But I think lugging is basically when the engine makes less on the power stroke than is needed to maintain rotation speed.

I think that's called deceleration. :p

Now if you meant when the pedal is mashed, that might be a little different story. :D

Billy_BAD_Boy 01-28-2010 01:06 PM

Quote:

Originally Posted by dcb (Post 148440)
ok, well in answer to the original question (and the title of this thread), it is as I described, load up the hill at bsfc peak and glide down and glide crawl over the top so you brake less.

Maybe we should change the thread title to "Hills (most efficient climbing technique for diesel / manual transmission after I put a whole bunch of conditions on it)" :)

Hi dcb,

Am I right saying that you advise climbing the hill with load above 50% of the accelerator pedal and in the sweet spot of BSFC map (low revs, highest gear and relatively high load)? If yes please correct me if I am wrong in the following:
We start climbing the hill as said above, with lets assume 2200 revs and 2/3 load on the pedal. We are in our BSFC sweet spot. Climbing the hill we start to unload the pedal to lets say 50% and our revs are going down to 1800. Theoretically we should loose torque faster than our fuel consumption is dropping. But what is the real world situation. I thing that when we are lightly unloading the pedal/revs are dropping we will have better fuel consumption than staying under constant load even though we are in our sweet spot.

It went kind a long but hope you understand what I mean.

Your or other opinions are highly appreciated.

Cheers


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