Subject line states my question. What factors at altitude can have an effect on mpg?
Does altitude affect mpg?
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Thinner air -> less drag -> more mpg. The gas up high tends to cost more, but the scenery makes the drive more enjoyable.
Unless you keep your driving to some high altitude plateau, driving at elevation involves going up hills a lot, so your MPGs suffer. But that wasn't really your question, was it?
Yes, the higher the altitude the worse your gas mileage. The higher the altitude the lower the oxygen content of the air, the lower the altitude (sea level) the higher the oxygen content. That's why at extreme altitudes you have to wear a oxygen mask so you don't pass out. Now, in a modern vehicle controled by a computer with oxygen sensors it can counteract this to a point. But no amount of injector pulse width adjustment will make up for extreme oxygen depletion completly. Problem would be most noticeable in a older carb type fuel system.
Interesting timing on the question. I just watched a program on Brazil (I think it was Brazil)the other night on the Documentry Chanel. Was about a very hazardours road that went through the mountains. The person in the program noted that his vehicle barely had power to crest hills when he was in the high altitudes and that he was experiencing light headedness and his body was tingling from lack of oxygen. When the vehicle returned to reasonable lower altitudes the vehicle was back to full power.
Interesting timing on the question. I just watched a program on Brazil (I think it was Brazil)the other night on the Documentry Chanel. Was about a very hazardours road that went through the mountains. The person in the program noted that his vehicle barely had power to crest hills when he was in the high altitudes and that he was experiencing light headedness and his body was tingling from lack of oxygen. When the vehicle returned to reasonable lower altitudes the vehicle was back to full power.
No, No, No.
You lose about 3% of your vehicle's horsepower for every 1000 foot in elevation. Given a 50 mile completely flat road at sea level and at 5,000 feet, your MPG will be better at 5K feet. It has nothing to do with the amount of oxygen to produce ignition, but the lower barometric pressures found at altitude.
You lose about 3% of your vehicle's horsepower for every 1000 foot in elevation. Given a 50 mile completely flat road at sea level and at 5,000 feet, your MPG will be better at 5K feet. It has nothing to do with the amount of oxygen to produce ignition, but the lower barometric pressures found at altitude.
I should add that this does not hold true for diesel engines.
A-U, it'll depend in part on how sophisticated the fuel system is on the vehicle. Carburated vehicles, even the constant velocity types, will suffer the most mileage loss. Modern FI engines, espeicially those with mass air sensors, will suffer less and sometimes improve.
Yep, improve.
My 2000 Triumph Sprint ST motorcycle (RIP) consistently got 45 MPG near sea level, yet would get around 60 MPG whenever I'd go to Colorado. I don't believe that this was riding style related, as the 45 MPG would hold true for trips within California. Only when I'd gain significant altitude would I get the better gas mileage. Other Triumph owners experienced the same, so it wasn't just my bike. I certainly felt the loss of power at altitude, though.
Yep, improve.
My 2000 Triumph Sprint ST motorcycle (RIP) consistently got 45 MPG near sea level, yet would get around 60 MPG whenever I'd go to Colorado. I don't believe that this was riding style related, as the 45 MPG would hold true for trips within California. Only when I'd gain significant altitude would I get the better gas mileage. Other Triumph owners experienced the same, so it wasn't just my bike. I certainly felt the loss of power at altitude, though.
Yes, agree with the posters that say that at elevation mileage improves. I noticed this in New Mexico driving on the relatively flat plateu's at about 5,000 feet elevation. When I kept the speed down, I got the best mileage I have ever seen by a considerable margin.
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I think that your power levels would change. That is, your peak hp would probably shift upwards in the rpm scale (maybe- or just be less at the same rpm level). Your system should balance out the fuel ratio ..but you're sucking in less dense air.
You can run higher compression pistons at altitude at the same octane rating without detonation. Your effected compressed fuel charge is lower.
You can run higher compression pistons at altitude at the same octane rating without detonation. Your effected compressed fuel charge is lower.
Modern EFI will compensate for altitude by using an HAC sensor if it's an L type system. A D type using an MAP doesn't need one. Strickly speaking the O2 content in the atmosphere is the same from sea level to space. It's the reduction in pressure that causes a problem. It's true that parasitic drag decreases with altitude though.
:OT: Isn't there something about playing the Denver Broncos, that passing the ball works better, and running with it is worse?
Turbocharged cars have totally got it made up high... except the best octane they can get might be lower as an oil company marketing decision. :banghead:
Turbocharged cars have totally got it made up high... except the best octane they can get might be lower as an oil company marketing decision. :banghead:
Says who? You listed several valid points about oxygen content and then followed up with an unsuported (and unsupportable) slew of personal opinions based on your personal opinion. Power loss, yes. Fuel useage at a given achievable speed at high altitude on flat terrain will be as good as at sea level. The limiting factors will be the maximum achievable speed at a given altitude and the achievable acceleration rate at a given altitude. Older deisel engines with no way to moderate fuel useage according to oxygen content smoked like the dickens at high altitude. That was unburned fuel curling out the exhaust pipe, no question - the fuel injection pumps had little or no provision for the amount of fuel injected. Those that did often required operator intervention to flip a two-position fuel cutoff lever (at least that was the arrangement on my '75 Mercedes-Benz 300D 5-cyl diesel car - I believe later models had an aneroid arrangement that accomplished that automatically.). But even naturally aspirated gasoline engines with modern fuel control systems will be virtually as clean and fuel efficient at altitude at any speed above idle as at sea level.
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Can I insert "percentage-wise" after the bold there ..and put a "(density)" after "pressure"?
That's just for those who will attempt to conduct high altitude breathing exercizes without the proper gear. You know that they would blame you for the lack of expected results.
(stray visions of that guy that did many jumps from a gondola at the 100,000ft mark in the 50's where his ballon looked like a sagging scrotum when he took off ..and then looked like a bulging onion when he jumped out-gotta love The History Channel).
At highway speeds, air drag accounts for about 2/3 of fuel consmption in a typical car. An electric car driving at 60,000 feet would get 200% better economy than at sea level.
Are you hassling me again Gary?
Yes, of course. My point was the level of O2 remains the same at appx 21% from sea level on up. Picture a cubic foot box of ISA (international standard atmospher, 29.92 in'hg @ 59 F). Let's say it has 21 green O2 marbles and 79 blue (N2) ones. We'll ignore the trace gases. As the box is raised in altitude the space between the green marbles spreads out but the number remain the same. It's this that results in less O2 being "inhaled" for a given volume by whatever is doing the inhaling.
Lol, I've already been spanked for posting my automotive credentials but the truth is I have education and experience in several disciplines. Such people, who choose to work in "lesser" jobs, aren't all that uncommom. Terry appears to be an example. I know a mechanic who has a PHD in physics. He simply enjoys wrenching for a living more than he did being a physicist. I fall into a similar category.
Yes, of course. My point was the level of O2 remains the same at appx 21% from sea level on up. Picture a cubic foot box of ISA (international standard atmospher, 29.92 in'hg @ 59 F). Let's say it has 21 green O2 marbles and 79 blue (N2) ones. We'll ignore the trace gases. As the box is raised in altitude the space between the green marbles spreads out but the number remain the same. It's this that results in less O2 being "inhaled" for a given volume by whatever is doing the inhaling.
Lol, I've already been spanked for posting my automotive credentials but the truth is I have education and experience in several disciplines. Such people, who choose to work in "lesser" jobs, aren't all that uncommom. Terry appears to be an example. I know a mechanic who has a PHD in physics. He simply enjoys wrenching for a living more than he did being a physicist. I fall into a similar category.
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What? Someone else is getting spanked? I'm usually the one open for abuse
Gotta learn to keep that foot clean ..since I often end up eating it.
I know what you meant. I'm just so misunderstood all that time that I, when I remember, qualify everything ..cuz sure 'nuff, if I leave out one qualifying tidbit ..what I've taken for granted will will be latched on to and shoved somewhere uncomfortable. It's considered a helpful public service to some (you're lucky it was me who did that to you. Some stranger could have done that. How would that make you feel? I care.)
Quickbeam, I like the analogy that you have posted for us. It provides a simple concept for visualizing the make-up of less dense air.
The Rocky Mountain region states tend to market gasoline with a 1 or 2 point reduction in octane, as higher altitudes and higher barometric pressures result in less dense air and lower octane requirements.
I think many people assume Higher Altitude causes less fuel economy...maybe because Higher Altitudes are commonly found in mountainous terrain. Perhaps it's the mountainous terrain that is the causative factor in less economy.
I live in appalachia and you guys are killing me with your straight road high altitude scenario's. Perhaps these do exist out west, but since I have never been there I cannot comment on it.
There is not a straight flat road around here. We go through brakes and tires at an accelerated rate as well. I have seen owners manuals that states living in the mountains is lumped in with a lot of stop and go driving and recomend the decreased OCI.
The best mileage I have attained was in the straight flat midwest with the cruise on.
There is not a straight flat road around here. We go through brakes and tires at an accelerated rate as well. I have seen owners manuals that states living in the mountains is lumped in with a lot of stop and go driving and recomend the decreased OCI.
The best mileage I have attained was in the straight flat midwest with the cruise on.
Funny how we live at the bottom of an ocean but the average person seldom thinks about it. I've been through several sessions in barometric altitude chambers. They take you up to 25,000 feet (the military guys go higher) and after removing the O2 mask give you simple tasks to do. It's amazing how quickly one becomes stupid after removing that mask. I still have the notes where I tried to sign my name. Starts out OK but by the end it ain't pretty. What was impressive during one of those chamber "rides" was watching through the window while a container of water begin to boil next to someone wearing a pressure suit. Yikes.
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