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I just thought of this yesterday and figured I'd throw it out for comments.

Lets pretend we're on a mountain road and maybe throw a trailer into the mix. There is a long down-grade followed by an uphill grade about the same length and percentage of grade coming up like a roller coaster ride. To get the most out of your fuel do you:

a) Coast down the hill saving there and power back up until cresting the next one.

b) Power down the hill (and maybe exceed the posted limit slightly ;)) using momentum to help climb the next hill. Less fuel used going down due to gravity assisting might fall into play.

c) Steady speed along the entire grade and hills but needing to power up the next hill from a nomimal speed at the bottom.

I know that in my situation with a fairly heavy (11,000 lb) 5th wheel trailer and our PSD powered truck it hates being pulled down in RPM on a hill. Loosing speed absolutly kills it on a hill. Is there a simple answer to this question? I'm looking forward to what PSIG has to say on this one as I respect his opinion greatly. Thanks all!

John
 

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It doesn't matter what we men think... Our wives are right.... always..

If you were to coast down the hill, adding only enough throttle to overcome friction, wind resistance, and gravity so that you would arrive at the top of the hill creeping along at 5 mph, that would be the most efficient use of fuel. Not very practical, though...

When I tow my rv, I like to get going fast enough to get my engine up above 3200 rpm where the torque band really starts, so it''ll carry me up the grade. Of course, if i can follow something big to cut the wind, it helps.

Momentum is your friend..
 

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Discussion Starter #3
It doesn't matter what we men think... Our wives are right.... always..

If you were to coast down the hill, adding only enough throttle to overcome friction, wind resistance, and gravity so that you would arrive at the top of the hill creeping along at 5 mph, that would be the most efficient use of fuel. Not very practical, though...

When I tow my rv, I like to get going fast enough to get my engine up above 3200 rpm where the torque band really starts, so it''ll carry me up the grade. Of course, if i can follow something big to cut the wind, it helps.

Momentum is your friend..
I'm with you on this (all three responses ;)) but wondered still what really is the best method. When in pulling in hilly terrain I'm not afraid to run up to....well, let's just say "faster than the posted limit" to get enough steam to make the next hill at around the posted limit, if that makes sense. With the PSD power keeping up with the flow of traffic isn't difficult. :tup: Like you, I know what works but is that really the most effecient way to do it?

John
 

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physics answer ... just like a roller coaster works
but maintain max down hill speed for up hill , must add power .

so for best mpg , freewheel down hill and coast down to speed limit , then add power .
. thats for best mpg not time taken . time and mpg could all go down the drain when the dude with lights pull you over . know max speed on the down hill run ? 90 +mph can happen
 

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Why don't you do your own experiments and share your results.
 

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From a practical perspective you will have to accelerate down hill as much as is safely and maybe just a bit illegally possible and then power on at the bottom starting up the next hill to maintain velocity. If you have the gears going to a lower gear will help. Letting the engine lug down is the worst for fuel economy. I have to do this pulling my car and I have some hilly roads to run going to and from the track. I sometimes have to pull down into second gear to pull a hill. My truck will run fine in second gear. I wish I had a granny 4 speed.
 

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OMG the pressure... LOL I note in your options, that you do not ask about mileage - but rather the focus seems to be on maintaining speed. Using speed can actually improve the MPG as well, considering it takes less fuel to climb a hill for 7 minutes at 90% throttle in 3rd gear than it does for 12 minutes at 75% in 2nd gear. In-fact, I actually have done experiments with this scenario, using an aftermarket ECM in a 3/4-ton and a weak small-block. With the laptop to read instant and average MPG, torque curve and all that, I found your Option B to work best for me and that truck with that load if trying to maintain speed. Option B also worked best when going from level to uphill, and also provided the best average MPG, so long as I did not push any harder to maintain speed on the uphill. Even more important, I found that it was very helpful to down-shift before it seemed 'necessary', as that would keep it above torque peak to avoid the lugging that Hottarod mentioned. Lugging is generally defined as the rpm that adding throttle does not provide acceleration.

Now, the question is why? Well, that's a problem, as each engine, total load, trans and axle gearing (and tire drag, aerodynamics, etc.) will give different results. It's important to assume here that the load and grade are too great to pull easily at the speed limit in high gear to the crest - otherwise, both speed and MPG would likely be best even WOT. However, in a general sense, a combination of A and B uses less fuel in a higher gear to accelerate to higher speed with the assistance of gravity at the bottom of the downhill, than coasting all the way down, and then trying to accelerate or just maintain speed. Unfortunately, that's often not possible and is obviously illegal.

There comes the other option - maintaining engine efficiency with gearing while maintaining legal speed or less. Depending on your total load and engine power curves, you may find you need different gearing for towing to keep it 'happy' and therefore efficient. The most common way to get that both with and without a trailer is with more transmission gears.

In a nutshell, if you're stuck with a certain load and maximum speed - but you're not limited by time or minimum speed - then balancing your load against your power curves with gearing will be most efficient for fuel economy. If you can't go faster than the speed limit, but you can't stand to slow too far below it - maintaining speed will cost you fuel. Simple as that. I'm not sure if that helps or not... LOL

David
 

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The answer is simple, just follow the Big Boys(trucks.)
 

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Discussion Starter #10 (Edited)
OMG the pressure... LOL
Sorry! ;)

I note in your options, that you do not ask about mileage - but rather the focus seems to be on maintaining speed.
I actually did ask about milage "To get the most out of your fuel do you:" and was my basis for the question. As you alluded too, fuel mileage and maintaining speed run hand in hand.

I found your Option B to work best for me and that truck with that load if trying to maintain speed. Option B also worked best when going from level to uphill, and also provided the best average MPG, so long as I did not push any harder to maintain speed on the uphill.
This is actually how I drive, especially when pulling the RV, but wanted to hear if this is actually the most effecient way. I guess I probably knew the answer but was curious to find out if I was right. If we're about to run up a long grade I'll try to slowly speed up as I approach the hill to get that momentum up.

Our truck is made to pull and I'm completly happy with the job it does. Being a dually it also has lower gearing (4.30 compared to the 4.10 used in most others) than most F350's which helps on those long grades.

The answer is simple, just follow the Big Boys(trucks.)
No way that's gonna happen. I can run away and hide from big rigs and any mountain road or grade. I hate getting stuck behind them on a hill 'cause then I have to slow down which kills my truck. I can run 55-60 MPH on a long 6% grade at altitude (6-7,000 ft) as long as I don't have to back way off. Then it takes a while to pick back up.

Why don't you do your own experiments and share your results.
Sure, I can hook up the trailer, drive a hundred miles to a area where I have long up and down grades, burn up three tanks of fuel trying the three different driving methods (40 gal x $4.50 = $180. $180 x 3 = $540) or I can ask the question here hoping that I get the right answer. I think I'll go take the $540 and buy something fun instead. We have some very intelligent people on this forum so as for me, I'm going to pick their brains and learn something.

Thanks all!

John
 

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Ah, I missed the "most out of your fuel", but the bottom-line answer is still the same. Which, BTW, isn't based on physics, calculations or anything, but the results I actually got testing it with the nifty data inputs, recording and graphing I had on the laptop with me for that trip. I just took it along to play with the tuning to avoid the endless boredom.

Interestingly, the greatest gain in fuel mileage besides driving style was from telling the injectors to completely shut off when the throttle was below 25%, the vacuum below idle levels, and when rpms were above 1100. This effectively shut the engine down any time I was coasting or decelerating - which is a lot more often than I thought it would be in hilly terrain or in traffic. The transition was smooth, and when the rpms fell to 1100, or I brought the throttle up, the engine would begin firing again and you couldn't even feel the cut-in. :tup:

David
 

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Discussion Starter #12
Interestingly, the greatest gain in fuel mileage besides driving style was from telling the injectors to completely shut off when the throttle was below 25%, the vacuum below idle levels, and when rpms were above 1100. This effectively shut the engine down any time I was coasting or decelerating
David,

How did you do this? I assume this isn't your everyday option on one of those hand held tuners like Bullydog or Superchips. Also, is this something that you continue to do as far as that "setting"?

Thanks,

John
 

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My take...

It doesn't take much energy to accelerate downhill with a load. The energy output is actually very minimal for the speed gained.

The extra speed/momentum can drastically shorten the time it takes to climb the next hill. Less time spent climbing is less fuel used.

So, easily accelerating down the hill using little extra fuel can pay dividends in climbing the next one... especially if it keeps the vehicle from needing downshifted... and saves a lot 'high throttle' time on the ascent.
 

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My take...

It doesn't take much energy to accelerate downhill with a load. The energy output is actually very minimal for the speed gained.

The extra speed/momentum can drastically shorten the time it takes to climb the next hill. Less time spent climbing is less fuel used.

So, easily accelerating down the hill using little extra fuel can pay dividends in climbing the next one... especially if it keeps the vehicle from needing downshifted... and saves a lot 'high throttle' time on the ascent.
agree . the problem is that extra speed can cost more in court than the fuel cost . btw . the fuel is a lot cheaper
 

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I used to tow the mustang on a dolly with a 1984 4cyl Ford Ranger. It had a 4.10 gear, 5-speed, and I installed a big radiator, cold plugs, synthetic fluids, etc. The back would also be loaded down to the top of the topper with nitrous bottles, fuel, tires, tools, tent, jack, chairs, spares, etc. These old trucks didn't weigh anything, and were gutless without a load. The engine was a TURD, had to make well less than 100hp with its 1bbl carb. lol Oh, I did add a header. lol

We would often go to races as a group, most of them between 3-6 hours away. Most of the guys had 460's and diesels.... or at least V8 powered full sized trucks. I had a really hard time keeping up on these WV hills... but we adapted a system. We all had CB radios, and on the downhills, I would let them know I was coming, and they would all move over. I might hit 85-95 mph wide open down the hills, and have a lot of momentum approaching the other side... then I might slow down to 45mph before making it to the top. I would pass them going down the hill, and they would pass me on the way back up. I ran a solid half tank of gas out of the truck without lifting the throttle off the floor. It was kind of dangerous, but was the only way I could keep up with everyone. lol Stopping was only up to the small brakes on the flyweight truck, so you learned to look WAY ahead and pay attention. Dangerous as a cocked cannon. (got around 10mph towing)

About that header... It would burn out the collector gasket after a single one way trip, so I would have to keep spares. That is, until one made of solid aluminum was purchased. It held up just fine. :)

Since then, I purchased an old 1976 GMC for $250 to tow with. Runs perfect... It's just ugly. It's a long bed and has a topper. Perfect for dragging the car to the track with. It just sucks the gas, and only gets around 12mph empty... and generally just sits in the garage until it's needed.
 

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Discussion Starter #16
My take...

It doesn't take much energy to accelerate downhill with a load. The energy output is actually very minimal for the speed gained.

The extra speed/momentum can drastically shorten the time it takes to climb the next hill. Less time spent climbing is less fuel used.

So, easily accelerating down the hill using little extra fuel can pay dividends in climbing the next one... especially if it keeps the vehicle from needing downshifted... and saves a lot 'high throttle' time on the ascent.
Mike, that's exactly how I tow the trailer and it's always worked out well. I usually don't go over 70 MPH on the downhills but since the towing speed limit here in CA is 55 max I'm exceeding it a lot. Heck, even flat towing I cruise at 62 ish all the time. The truck just likes running at that speed (right at 2,000 RPM) and will creep up there almost on its own as weird as that sounds.

When towing in states that have no "towing" speed limit I still cruise at around 65-70 just to make the most out of my fuel. With the 5er on the back it gets a solid 10 MPG in all but the worst conditions but we're also right at 20,000 lbs loaded (I've weighed it) so that's no surprise.

Thanks all!

John
 

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David,

How did you do this? I assume this isn't your everyday option on one of those hand held tuners like Bullydog or Superchips. Also, is this something that you continue to do as far as that "setting"?

Thanks,

John
John, sorry about the delay - FM isn't sending me notifications of replies consistently. :bicker: Anyway, yes, it's a standard for me and all my setups with manual trans or auto with lockup use it. It won't work with most non-lockups as the car motors the dead engine for restart. '95+ Ford OBDII use it, and earlier ones often have the capability, but were crippled or not enabled. For example, the Mustang A9L has it, but crippled. The A9P does not have it enabled, but it can be re-flashed with better compatible code (such as the X3Z code) to make it fully functional.

While most systems can be made to use it with the right hardware/software, I have pretty-much left the hacked factory ECM party and have settled primarily on MegaSquirt. MS lets you do all this in any way you want (none/partial/full/when/how) and a ton of other stuff, so there is no arguing with factory coding schemes, speaking code language, or jumping hurdles. If you have a Ford EEC, and a pro-tuner near you with the right stuff, he can burn code or enable and adjust it in a Ford EEC for you.

Yes, it saves a considerable amount of fuel over carbs or EFI that don't have it, depending on the vehicle and driving style.

David

Here is an example of the decel (over run) fuel cut settings. Note EFI uses kPa or millibars as a universal pressure standard instead of inches of vacuum, and this engine idles at 30 kPa (about 21" of vacuum - WOT is about 100 kPa). TPS is the throttle position sensor. So, when the rpms are above 1100, the vacuum is below idle level, and the throttle is close to closed, all injection is shut off. If any of the parameters are exceeded, the injectors turn on and the engine runs normally. You can easily play with the levels to see what your engine likes best. Just change a number and "Burn". Instant results:
 

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David,

Wow, that's way more tech than my brain can handle but it sounds like good stuff. I wish I had the patience to learn that stuff so I could take advantage of it too!

Thanks,

John
Nagh it really isnt, you DO remember your FIRST computer dont you?;)
 

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John, sorry about the delay - FM isn't sending me notifications of replies consistently. :bicker: Anyway, yes, it's a standard for me and all my setups with manual trans or auto with lockup use it. It won't work with most non-lockups as the car motors the dead engine for restart. '95+ Ford OBDII use it, and earlier ones often have the capability, but were crippled or not enabled. For example, the Mustang A9L has it, but crippled. The A9P does not have it enabled, but it can be re-flashed with better compatible code (such as the X3Z code) to make it fully functional.

While most systems can be made to use it with the right hardware/software, I have pretty-much left the hacked factory ECM party and have settled primarily on MegaSquirt. MS lets you do all this in any way you want (none/partial/full/when/how) and a ton of other stuff, so there is no arguing with factory coding schemes, speaking code language, or jumping hurdles. If you have a Ford EEC, and a pro-tuner near you with the right stuff, he can burn code or enable and adjust it in a Ford EEC for you.

Yes, it saves a considerable amount of fuel over carbs or EFI that don't have it, depending on the vehicle and driving style.

David

Here is an example of the decel (over run) fuel cut settings. Note EFI uses kPa or millibars as a universal pressure standard instead of inches of vacuum, and this engine idles at 30 kPa (about 21" of vacuum - WOT is about 100 kPa). TPS is the throttle position sensor. So, when the rpms are above 1100, the vacuum is below idle level, and the throttle is close to closed, all injection is shut off. If any of the parameters are exceeded, the injectors turn on and the engine runs normally. You can easily play with the levels to see what your engine likes best. Just change a number and "Burn". Instant results:
those numbers don't make sense .. how I read it the engine shoud'nt run

over run equal bypass/turn off fuel shut down ? only then it would run
 
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