Optimum speed for best mileage is 65 MPH?

[IZwack]

Wow eggos.. wait i mean egos. Guys lets chill .. on a more serious note (more serious than MPGs obviously), anyone care to go watch Mama Mia with me? . Yes thats right, we can dance, we can jive -- having the time of our lives.

 

[gijoecam]

You guys are starting a pissing match about the ideal mileage for an Explorer... It's not going to be the same across the board. There are too many variables from one vehicle to the next. As I already mentioned, simple, seemingly insignificant things like tire size, inflation pressure, whether or not you're running synthetic fluids, whether you drive with the sunroof vented or wide open, etc. all play into the equation. For Al, he's found that with whatever mods he's done to his truck, the ideal speed is 55-60. For me, I've found the ideal speed is 65. Someone else may find there is as low as 45 or as high as 80. It's all dependent upon your particular vehicle and your particular setup.

One can do all the calculating in the world when it comes to power/torque curves, but that doesn't mean a hill of beans on the open road. Change the frontal area by a square foot (say, with a bug deflector), disrupt the airflow in a wierd way (say a roof rack?), put on tires with a little bit more rolling resistance (BFG All Terrains anybody?) and it'll all have an effect. Not all of them will reduce the mileage either... it's a guessing game at best. At best, one could make an educated guess, but it's still just a guess.

-Joe

 

[Russ in CT]

I couldn’t agree more. The only thing I took exception to was that Aldive had commented about the best mileage for ‘the Explorer’. HIS Explorer maybe, just not necessarily EVERY Explorer. Hence my question about how many times he’s tested the mileage on Mr. Wizard’s Ex (I was trying to imply it was quite possible a completely different ideal speed). Maybe I could have used a little more tact.

I don’t understand how Aldive does it, I’ve been driving around for the past few months, NEVER exceeding 2.5K rpm’s, and almost never exceeding 2K. From a stop I’m accelerating slower than a moped (not an exaggeration), and on the highway I’m cruising at 2K rpm’s or less (usually less). Up hills I’m even more careful, I don’t let it downshift, I might end up going only 40 mph on the freeway up hills. I’m practicing hypermileing tricks, like staying off the brakes (and other things). I’ll approach a stoplight and slow down early (without brakes), hoping to get the green while I’m still moving well along, while I still have momentum. At every point while driving I’m imagining how much effort it would be if I were on my bicycle, and adjust my driving so as to minimize the demand on the engine (the way I would minimize the demand on my legs if I were pedaling). My driving is pretty much to work and back, 40 miles each way, 90% of which is highway (and I don’t hit traffic any bumper-bumper traffic), and the rest is 30 mph backroads, with just a couple of stop signs. All this, and the best I can get is 22 mpg (’99 Ex XLT, 4.0 SOHC, very similar to Aldive’s).

So I’ve got a lot of respect for what Aldive as been able to accomplish, he completely blows away my best efforts, like Michael Phelps vs, well, me. But that doesn’t alter the fact that his results aren’t automatically transferable directly to every other version of the Explorer.

 

[aldive]

. The only thing I took exception to was that Aldive had commented about the best mileage for ‘the Explorer’. HIS Explorer maybe, just not necessarily EVERY Explorer.

Granted the vast majority of my testing has been on my current Explorer. However, I have evaluated speed vs MPG on 7 other Explorers and had similar results.

Hence my question about how many times he’s tested the mileage on Mr. Wizard’s Ex (I was trying to imply it was quite possible a completely different ideal speed). Maybe I could have used a little more tact.

Haven't had the privledge to drive that amazing machine.

So I’ve got a lot of respect for what Aldive as been able to accomplish, he completely blows away my best efforts, like Michael Phelps vs, well, me. But that doesn’t alter the fact that his results aren’t automatically transferable directly to every other version of the Explorer.

What modifications have you made to your truck to improve gas mileage? Have you tuned the PCM?

 

[MrWizard]

logging data

I kinda think my Explorer is rather ordinary! ( Other than it's been the most phenomenally
reliable vehicle I've ever owned.) It certainly gets a very ordinary 17 MPG in mixed driving.

One of the reasons I started on this measurement campaign was to understand "where the heck is all the gas going?"
And even though I'm measuring everything thoroughly, there is no substitute for cross checking with everyone else.

And I don't know how Aldive does it either. But I do think one of the keys to making any improvement is to
learn what everyone else before you has done, understand why it works and gauge the relative importance
of each factor. That way you're not spending a lot of time or money futzing around with insignificant items.

Just recording my own instantaneous fuel consumption on my laptop was insightful. If you're
serious (Russ) about improving your gas mileage, there's no substitute for actually measuring it.

A lot of the advice floating around is non-quantitative, and pretty loosely justified. Although
sometimes a MPG meter seems like a random number generator, so I digitally log the data for later.

So what have I learned by logging all this data?:

* During the first couple of miles on a cold engine the fuel consumption was 70% higher. And even
after the engine warmed up, the fuel consumption only gradually decreased as the engine got hotter.
This explains why your gas mileage goes to hell in cold weather. It's going to be tough to beat Aldive's
mileage in Florida And if you only do short trips, your gas mileage is gonna be absolutely awful.

* My optimum highway speed for best mileage is a very non-intuitive 65 MPH.

* When you let off the gas and coast (on flat ground), the PCM keeps the RPMs artificially high and gradually floats them down.
This makes for a very smooth transition and apparently reduces NOx emissions, but certainly doesn't help your mileage.
Is this one of the areas where a custom PCM tune can help, by cutting fuel flow more while coasting?

* Turning on the A/C at idle increased fuel consumption 25%. And dropped it 10-20% at other speeds.
This is predictable since the A/C compressor consumes ~3HP at idle and the engine itself is only
putting out around 12 HP at idle. A car A/C compressor puts out a massive 16,000 BTUs, or more.

* An airflow/airfilter restriction increased fuel consumption. This was somewhat counterintuitive for me, since I thought the
MAF would tell the PCM that the airflow was less and hence lower the fuel flow. Nope. It bumped the RPMs up to compensate
for the restriction and consequently increased the fuel flow. A clean air filter is a lot more important than I would have thought.

* Couple of interesting conclusions from this chart. Always at 1700 RPM but different conditions:

_RPM_ , _SPEED_, TOTAL FUEL = overhead + load , _MILEAGE_, CONDITION
-------- ------ --------- -------- -------- ------- ----------------
1700 RPM, 00 MPH, 1.23 GPH = 1.23 GPH + no load_ , 00 MPG, Reving in PARK
1700 RPM, 23 MPH, 3.42 GPH = 1.23 GPH + 2.19 GPH , 07 MPG, Climbing hill
1700 RPM, 40 MPH, 3.01 GPH = 1.23 GPH + 1.78 GPH , 13 MPG, lower gear cruising
1700 RPM, 45 MPH, 0.00 GPH = 0.00 GPH + no load_ , 99+MPG, Coasting downhill
1700 RPM, 65 MPH, 2.32 GPH = 1.23 GPH + 1.09 GPH , 28 MPG, O.D. cruising <<

* You waste about half your fuel just running the engine and accessories. In this chart, at 65MPH my
total fuel flow is 2.32 GPH, of which 1.23 GPH is simply due to the engine running unloaded (overhead)
at 1700 RPM, and the remaining 1.09 GPH is needed to overcome inertia, friction and drag (load).

* Hills kill gas mileage. Even if you coast downhill and keep steady pressure on the gas pedal climbing,
(not accelerating to maintain speed). Never seems to be the ideal case of preserving kinetic energy.

* Spending any time in the lower gears kills your gas mileage as well. (I don't understand why my city mileage is
this bad though. The tranny losses can't be this much, can they? This is what destroys my overall average mileage.)

Russ, there's a hypermiler school of thought that suggests you not accelerate like a grandma, but accelerate briskly
at an RPM near the center of your partial throttle torque peak, get through the lower gears quickly and get
into overdrive as soon as possible. The trick is not to accelerate too hard, or you go above the torque peak
and get really bad mileage. (I dunno if this is a wash, or it really makes a difference. You expend more gas
accelerating faster, but you spend less time in each lower gear.)

Anyway, if any of these contradict what you know, through data, or experience, glad to hear about it.

 

[MrWizard]

BSFC and P&G

An interesting article about "Brake Specific Fuel Consumption":
http://autospeed.com/cms/A_110216/article.html.

Also, if you're driving a lot of highway miles has anyone considered using the "pulse and glide" technique?
This supposedly gives you much better mileage than using cruise control (and not just for Hybrids).

As I understand the concept, you accelerate at your optimal rate to say 65, let off the gas and coast down to 55,
accelerate up to 65, coast.... Seems like a bit of a hassle and you probably drive everyone around you nuts,
if you don't drive on a lightly travelled highway, but the mileage gains seem impressive.

 

[joecrna]

See pulse and glide in LA stop and go 87 miles each way every day. MPG goes up 20%. Im a strong believer in BSFC but the trade off of areo resistance varies with each vehicle and I don't have a wind tunnel. So perfect gearing and maintaining perfect corresponding speed is out of the question. Pulse and glide never really made great sense to me but hypermilers get phenomenal results with this technique only used over a much wider speed range.

Don't forget, pumping losses (ie.against a closed throttle plate) are an engines worse enemy. They account for 15-20% of the improvement a deisel engine sees over gasoline.

PS. My sports car loves 80 mph. Slower and I get slightly worse mileage. Faster and gas mileage drops like a rock.

 

[Russ in CT]

Mr. W, you saw a 10-20% drop driving around with the A/C on. What about opening the windows? Can you run a test that measures this effect?

I've found that if its not too hot, I can crack the passenger side and two back windows (and leave drivers window closed), and create a swirl effect that generates a surprising amount of cool breeze over drivers area. Works quite effectively when I'm driving alone. It seems more effective than just opening all the windows, and is much more tolerable sound wise.

I'm doing this not so much for mileage, but because my A/C is on its way out, but I've been wondering if the additional drag I'm creating is worse (for fuel mileage) than using the A/C would be (if it were working 100%).

I'd bet that opening the windows most of the way, even just one or two of them, is way worse than using the A/C, due to the drag. But I'm curious to see what cracking them open, say 3 windows, 5 inches each, does.

Also, can you tell us more about your program that you're using to measure these paramters? How does it hook into the sensors? What was it written in (can it be compiled into something distributable to run on other PC's?)

Maybe you could send it to some of the rest of us, to test & refine, then you could sell it to consumers? Imagine if everyone had access to this data, a realtime measure of your fuel economy? My wifes car has this in its 'computer' display (but in using it its always seemed to me to be dumbed down, and with a long update delay). But so many vehicels don't have even this, and so many people want (need) imperical data about their fuel usage. I would think if you could make it into a usable kit, a lot of people would buy it.

 

[Russ in CT]

Just read the article about BSFC. I recall something my father told me about almost 30 years ago. Seems he had been invovled in this project back in the 50's to build a prototype high fuel mileage car.

They fitted a Nash Metropolitan (or maybe it was the Rambler?) with a CVT, and arranged for the throttle and CVT to work together such that the engine was at WOT most of the time, with the CVT keeping the revs at bay by gearing up high as needed, varying the load. So it was essentially a form of drive by wire, although they didn't have any computer technology back then, so I'm not sure how they accomplished this.

But the idea was to keep the throttle open, reducing pumping loses. This goes right along with the SFC charts in that article.

Imagine what could be accomplished today with this concept?

Think too, that none of this info is new, it was known way back then. If fuel economy had been more of a priority for more of the past 50 years, think of what could have been accomplished by now?

 

[MrWizard]

measurement

I'll measure the window up/down/cracked open a bit vs. A/C the next time I'm out with the test setup.
Most likely cracking the windows is better than A/C until you get up to some pretty high speeds.

btw, my test setup was described in an earlier post in this same thread. I have it connected to the VSS signal (speed) and
injector signals through a resistor/diode circuit to keep from overloading my PC's audio input. There is a similar sort of program
written in Java floating around the web. You can find it by googling MPG.java. They use a similar circuit as well.

The only reason I wrote my own program was I wanted to use an old junk laptop, which can't run Java, and I wanted to log the data,
since it is a pain to drive and analyze data at the same time. "Sorry officer, I was resizing my EXCEL columns and suddenly that car pulled out..."
Plus my Explorer is pre-OBD-II. Otherwise, I could have just bought a scangauge and measured fuel flow and MPG thru the diagnostics port.

 

[Tom Brown]

Judging by the telemetry in my 2000, 4 door, 4x4, 4.0 SOHC, Limited and also my ScanGauge II, I get best fuel mileage at just below 50 mph (perhaps 46~48). It stays pretty decent until 55 and starts dropping.

Typical flat, no wind driving mileage:

50 mph - 23 mpg
55 mph - 21.5 mpg
60 mph - 19.5 mpg
65 mph - 17 mpg

 

[joecrna]

That may explain my 15mpg going to Pheonix last week. One tank was 13 flat but I was running late for a conference. God bless Cinncinatti Microwave.

 

[Nedwreck]

ooh. wow. Great Thread!

Mr. Wiz, thanks for the terminology and explanations on the torque/RPM/load relationships. Great stuff, I simply didn't have the words to 'splain to my friends how many of these things work.

I don't have alot to add, but do want to observe that some of the principles mentioned have worked great for me..

My old '78 F150, 2WD is a great example. 400/C6/2.70 drivetrain. 265/75-15's. Cruise RPM about 1800-ish. After a few tweaks was a good 16-18 mpg truck. It lives one town over now with a good friend, and serves him well.

The layman's terms I use is... more torque, less throttle = better MPG. I can see I'll have to revise that some. Tweak for torque, and let it do the work.

I also agree that it's often better to go ahead and get that puppy on up to speed and keep it there. Moderate acceleration of course.

 

[Mightycline]

I just want to say that I am getting 25+ MPG in my 2006 Explorer XLT V-6 4X4 on the Interstate around Illinois, Michigan, Illinois, Wisconsin and Indiana at 59+MPH. At more speed, I get less MPG as should be expected by mortal folks. Examples are 23+ MPG at 63MPH, 21MPG at 66MPG; 19MPG at 67 MPH and 18MPG at 71MPH. Simple accurate gas fill ups with some log notes in my Franklin Quest Planner and an easy check against the mileage indicator with hard numbers coming from accurate gas station fill-ups........I am able to drive from Indiana to Detroit, Cleveland and over Minnesota at 24+MPG using 87 Octane with 10% ethanol. Get better with 100% gas which I can get locally here in my home town in NE INdiana. Best gas prices this week are in Minnesota at $3.299 and falling everywhere except Cook County Illinois. I have tires inflated to Mfg numbers and nothing special in tread. Happy with these results as I could never justify owning any vehicle that gets 18MPG at 59MPH.....so I get 23-25MPG consistantly. I drive to Texas, Florida, Outer Banks NC, Montauk Long Island NY and looking forward to the very real MPG challenge of the Rockies in this truck. Keep on trucking, you just might want to go a little slower?! Mightycline

 

[Blue_Oval_Ford]

With all the Mods I have done to my truck here is what I get on the Highway.

50 mph: 25.2
55 mph: 23.6
60 mph: 22.1
65 mph: 20.3
70 mph: 16.2
75 mph: 14.5

It seems anything over 65 mph and my X starts eating gas like crazy

 

[aldive]

Just returned from a long road trip.

453 miles @ 65.2 MPH = 31.8 MPG
return leg
@72.4 MPH = 28.1 MPG

 

[shortstack]

from what i've noticed is 50mph, the rpms is around 1.5k (in 3rd gear i believe) where as 65mph is around 2.4krpms.