Topic: what happens to cars at higher altitudes?

[drewtoo]

i basically want to know what happens to cars at higher altitudes. does fuel consumption go down because their is less drag or does it go up because their is less air for the engine to consume? if it does move around, how much difference would it be if i were on sea level?

[JacobBlack]

I drove across the Andes in Argentina and Chile twice. Highest I got was 4,600m above sea level. At 2,500m the engine in the Fiat Sienna (1st year)  and Ford Escape (2nd year) were both not breathing in enough oxygen. I was flat-out in third just to keep it going at 60 km/h.
Fuel consumption goes through the roof because you have to use way, way more fuel. I think we went from about 400 km of range to about 300 km of range in the little Fiat.
Altitude is bad news for engines.

[drewtoo]

thats good to know, ill have to factor that in on snowboarding trips. does the cold also effect economy a lot too?

[HeliDriver]

I drove across the Andes in Argentina and Chile twice. Highest I got was 4,600m above sea level. At 2,500m the engine in the Fiat Sienna (1st year)  and Ford Escape (2nd year) were both not breathing in enough oxygen. I was flat-out in third just to keep it going at 60 km/h.
Fuel consumption goes through the roof because you have to use way, way more fuel. I think we went from about 400 km of range to about 300 km of range in the little Fiat.
Altitude is bad news for engines.

You sure the lousy fuel economy wasn't just because of the mountains you were climbing? Going uphill is always going to get you worse mileage than cruising on the flats.

A fuel injected engine is only going to inject as much fuel as there is oxygen available to burn it. Less dense air at altitude means less oxygen available means less fuel injected, not more.

And engines are actually more efficient at wide open throttle than at partial throttle, so having to floor it just to produce the same amount of power as at lower elevations should help fuel economy, not hinder it.

[tpl]

The answer to using a car at altitude is to buy a turbocharged car.   I'd also say supercharged but I suspect that you'd need to change the drive pulley and belt for high altitude driving. In thinner air the turbo will spin faster and partially solve the problem. 

If you think about it, all those famous high performance WWII piston engined aircraft with forced induction for power AND to keep that power at altitude.

[Patrick_D1]

I drove across the Andes in Argentina and Chile twice. Highest I got was 4,600m above sea level. At 2,500m the engine in the Fiat Sienna (1st year)  and Ford Escape (2nd year) were both not breathing in enough oxygen. I was flat-out in third just to keep it going at 60 km/h.
Fuel consumption goes through the roof because you have to use way, way more fuel. I think we went from about 400 km of range to about 300 km of range in the little Fiat.
Altitude is bad news for engines.

You sure the lousy fuel economy wasn't just because of the mountains you were climbing? Going uphill is always going to get you worse mileage than cruising on the flats.

A fuel injected engine is only going to inject as much fuel as there is oxygen available to burn it. Less dense air at altitude means less oxygen available means less fuel injected, not more.

And engines are actually more efficient at wide open throttle than at partial throttle, so having to floor it just to produce the same amount of power as at lower elevations should help fuel economy, not hinder it.

HeliDriver is right; the lower air density results in lower power output. With a reduced air intake volume, the engine can't inject as much fuel. In turn, the reduced power output necessitates larger throttle openings to climb the grade, harming fuel consumption.

[Bubba]

NHRA has this handy Altitude Correction Process document.  It shows how much performance you lose at the track due to the altitude.

For example, if your car can run the quarter-mile in 15.00 seconds at sea level, it should run approximately 15.95 seconds in Denver, CO.  Definitely noticeable.

[HeliDriver]

I drove across the Andes in Argentina and Chile twice. Highest I got was 4,600m above sea level. At 2,500m the engine in the Fiat Sienna (1st year)  and Ford Escape (2nd year) were both not breathing in enough oxygen. I was flat-out in third just to keep it going at 60 km/h.
Fuel consumption goes through the roof because you have to use way, way more fuel. I think we went from about 400 km of range to about 300 km of range in the little Fiat.
Altitude is bad news for engines.

You sure the lousy fuel economy wasn't just because of the mountains you were climbing? Going uphill is always going to get you worse mileage than cruising on the flats.

A fuel injected engine is only going to inject as much fuel as there is oxygen available to burn it. Less dense air at altitude means less oxygen available means less fuel injected, not more.

And engines are actually more efficient at wide open throttle than at partial throttle, so having to floor it just to produce the same amount of power as at lower elevations should help fuel economy, not hinder it.

HeliDriver is right; the lower air density results in lower power output. With a reduced air intake volume, the engine can't inject as much fuel. In turn, the reduced power output necessitates larger throttle openings to climb the grade, harming fuel consumption.

Well, that's not quite what I was saying. Larger throttle openings should be good for fuel economy, not bad. That's why BMW got rid of the throttle plate completely and went with their Valvetronic instead. The engine is running at WOT all the time (well, actually there is no throttle, but it's kind of the same thing) and they realized something like a 10% improvement in fuel economy, IIRC.

I think there are two separate discussions to be had here: power loss at altitude is the easy one, but fuel economy at altitude is the more interesting one.

Maybe if the car is so underpowered to start with that you wind up using both a larger throttle opening and a lower gear, then you'd see a decrease in fuel economy. But if it's a question of being at the same speed, same gear, same rpm in a constant cruise, then the engine is making the same horsepower (oops, actually less horsepower because of the reduced wind resistance), just at a larger throttle opening, which is not a bad thing.

People usually think in terms of the "gas" pedal, which it really isn't: it's more of an "air" pedal. Just because your foot is to the floor (at altitude) doesn't mean the engine is getting more gas (than it would at sea level.)

[JacobBlack]

Heli, like I said already, I had to run a lower gear. Even on flat sections. Hence fuel economy is belted at altitude. You're 100% right,  any time you're engine is running higher rpm to do the same job economy is screwed.

[phazotron]

Ok, everything else being equal, if you are at the much higher altitude with the much thinner air, will that increase engine temperature or not?  My only experience with mountain driving is going up the road at Whiteface that ends near the summit during which I saw the temp needle on my van go higher than it ever did under any other driving condition.  I chalk that up to the really steep climb.

[HeliDriver]

Well, it's air going through the rad that takes the heat away, so I figure that less-dense air would have less ability to do that. For example, I'd assume the engine would get hotter climbing a 12% grade from 6,000' to 10,000' than it would climbing the same grade from 2,000' to 6,000'.

[johngenx]

I've driven over the high passes in our nation (Highwood, Kootenay, Bow, Sunwapta, etc, etc) and altitude isn't a big concern in Canada.  At 2200M, yeah, performance is affected, but it's the steep grades that are more of a concern.

[Fobroader]

Watch the Top Gear special where they drove across the Andes. It answers all the questions, and is funny too.

Perfect way to see what happens.

Sent from my Galaxy S3

[G35X]

1.　Energy required to move a mass is same at any altitude. Though, to be precise, the higher the altitude,
the less energy is required because of lower "G" and air drag. And, the amount of fuel required to produce
a certain amount of energy is same regardless of altitude.

2. With an NA engine, maximum engine output becomes about 10% less at 1000 meters, 20%less at 2000
meters and 30% less at 3000 meters compared to the output at the sea level. This means a car's maximum
performance numbers, such as max speed and acceleration, deteriorate as we go up higher. We can feel this
reduction of max power when going up a steep hill at, say, 3000 meters with the gas pedal all the way to the metal.

3. As HeliDriver and others already mentioned if deterioration of fuel consumption is observed, that's because
of hill climbing rather than thinner air. In older days(before oxygen sensor and fuel injection)we used to waste
fuel by stepping on it too much making the air/fuel mixture too rich. But these days that is not possible.
Speaking of hill　climbing, if a car has energy recovery system (hybrids) it can somewhat compensate the increase
in fuel consumption by recouping some energy when going downhill.

4. Thin air is the reason why electric cars are now dominating the Pikes Peak(4301 meters) Hill Climb race.

[rrocket]

Nothing at all happens...juts be sure you're driving a Tesla!   

[Great_Big_Abyss]

To be honest, though, when driving to most places in NA where you can drive your car to a ski-lodge you won't have to modify your driving style drastically to get there.  Maybe you car will be less willing to pass on an undivided highway, especially if you're loaded down with passengers and equipment, but really, you probably won't notice a HUGE drop in power.  Don't forget, most ski lodge parking lots are at the BOTTOM of the mountain!