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Engines at Altitude

dweskamp

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Go a little further north in Castle Rock. Very nice area, if you can afford it.
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69BroncoX302

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Hi all. Apologies if this has already been covered - I searched around but couldn't find anything. I'm in Indiana, so I didn't have any concerns with the 2.3, but I'm considering a move to the Colorado Springs area. I'd be driving at high altitude a lot, and I wondered if I should have any concerns. Obviously, it's not naturally aspirated, so that's good. I don't know if modern cars have made big improvements in regards to handling altitude: like I said, I'm from Indiana. I believe the highest point in the state is ~900 feet. I'd like to hear from some of you who have dealt with these powertrains at altitude. Would I need to upgrade to the 2.7? I would also really like a manual, so that's my other reservation toward the upgrade aside from the cost. From what else I've read on the subject, it doesn't seem like it should be much of an issue, but I'd still like to hear some opinions.

P.S. If anyone has some opinions of CO Springs, I'm all ears. That's taking it way off topic, but oh well. I've visited before, but not for any meaningful amount of time.
the MAP, MAF and other sensor will accommodate, not to mention its turbo'd. I lived in CO for a few years and had zero issues with my 2.5 EJ257 STi motor. Have fun in the springs if ya go. GRANTED, you will feel it more then the bronco will.
 

KingWillard

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I live at 7000 feet and have had the Bronco as low as sea level and as high as 9000 feet. I don’t doubt there is a little difference in power, but I have not noticed much, if any at all (totally subjective). I have a 2.3 manual Black Diamond.
 

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Definitely effects your fuel economy.


Altitude (feet)Altitude (meters)Effective Oxygen %Altitude CategoryExample
0 ft0 m20.9 %Low AltitudeSea Level
1000 ft305 m20.1 %Low Altitude
2000 ft610 m19.4 %Low Altitude
3000 ft914 m18.6 %Moderate Altitude
4000 ft1219 m17.9 %Moderate Altitude
5000 ft1524 m17.3 %Moderate AltitudeBoulder, CO (5328 ft)
6000 ft1829 m16.6 %Moderate AltitudeMt. Washington (6288 ft)
7000 ft2134 m16.0 %Moderate Altitude
8000 ft2438 m15.4 %High AltitudeAspen, CO (8000 ft)
9000 ft2743 m14.8 %High Altitude
10,000 ft3048 m14.3 %High Altitude
11,000 ft3353 m13.7 %High AltitudeMt. Phillips (11,711 ft)
12,000 ft3658 m13.2 %High AltitudeMt. Baldy (12,441 ft)
13,000 ft3962 m12.7 %Very High Altitude
14,000 ft4267 m12.3 %Very High AltitudePikes Peak (14,115 ft)
 
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69BroncoX302

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Definitely effects your fuel economy.


Altitude (feet)Altitude (meters)Effective Oxygen %Altitude CategoryExample
0 ft0 m20.9 %Low AltitudeSea Level
1000 ft305 m20.1 %Low Altitude
2000 ft610 m19.4 %Low Altitude
3000 ft914 m18.6 %Moderate Altitude
4000 ft1219 m17.9 %Moderate Altitude
5000 ft1524 m17.3 %Moderate AltitudeBoulder, CO (5328 ft)
6000 ft1829 m16.6 %Moderate AltitudeMt. Washington (6288 ft)
7000 ft2134 m16.0 %Moderate Altitude
8000 ft2438 m15.4 %High AltitudeAspen, CO (8000 ft)
9000 ft2743 m14.8 %High Altitude

not quite, less oxygen in the air mean less fuel to achieve the proper AFR.
 

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Seacat

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not quite, less oxygen in the air mean less fuel to achieve the proper AFR.
All I know is when I go back to Wichita Kansas (1000 ft) to visit family, my diesel Touareg gets about 1 to 2 mpg better fuel economy than in Colorado (6500 ft).
 

Gotdesl

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Just got back from day 2 elk hunting above 10k feet in the 2.3/7 speed. While not going for all out speed, off roading will definitely test the performance of the engine. I have no issues whatsoever with this thing at altitude. It has plenty of power to do whatever I ask of it and I don't have to flog it to get it done. Caveat being that I've never driven it below 5.5k feet or so.
 

RedDawg

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I can confirm, my trade in for the Bronco was a 2019 Toyota 4Runner TRD Off-Road. Above 6000 feet that thing was terrible. It barely was able to pull a tiny 2000 lb trailer. I had to crawl over Wolf Creek Pass st 35mph. With the Bronco 2.3 with AT, zippy snap, no issue at all.
@mountainbronco
Have you towed your 2K lbs trailer with your Bronco yet? How’d it do going up grades?
 

mountainbronco

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@mountainbronco
Have you towed your 2K lbs trailer with your Bronco yet? How’d it do going up grades?
good morning, no, did not yet trailer, but I have no doubts at all that the 4 cylinder will handle that with ease. Now I have by BD delivered, which has the 2.7 and this thing could easily handle 5000 lbs, if the Bronco only could...........

I am 100% confident in the 2.3 abilities! (that was a loaner I got a did 2000 miles on it)
 

BDSteelies

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As a general rule, a naturally aspirated combustion engine will lose 3% of its power for every 1,000 ft of elevation gain. If you have 100 horsepower at sea level by the time you get to 5,000 feet of elevation your engine is making 85 horsepower.
Turbocharging at elevation is an efficient way to minimize horsepower loss due to elevation and lower air density. At high elevations turbochargers compress more air into the engine cylinders making up for the lower air density allowing the engine to produce power as if it was at sea level. This extra tunability is found only in turbocharged applications.
This ^ but always quote your sources!! :p
https://www.garrettmotion.com/news/...at-elevation-counteracting-lower-air-density/

TLDR: Difference in air compensation (% oxygen) at altitude is negligible, so as long as the turbo can handle the increased RPMs required to pump the lower density air to the same boost pressure, then the engine will compensate and produce the same power produced at sea level.
 

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Is that really true? Genuinely wondering. I thought the overall make up of the air (% of O2, % of N, etc) is still the same, there's just less of everything in a given volume. So if the turbo is compressing the mixture to the same PSI as it would at sea level, it would give you about the same oxygen for burning, therefore produce about the same HP. Is that not correct?

Also, with my previous cars, especially on stock tune, the turbo is capable of producing way higher pressure than the ECU allows. So I would expect the turbos to be more than capable of compensating at altitude. With aftermarket tune, the requested pressure is a good deal higher, so there's less margin above that, then the smaller stock turbos could run out of efficiency and not produce the same PSI as it would at sea level.

No?

Peter
As a general rule, a naturally aspirated combustion engine will lose 3% of its power for every 1,000 ft of elevation gain. If you have 100 horsepower at sea level by the time you get to 5,000 feet of elevation your engine is making 85 horsepower.
Turbocharging at elevation is an efficient way to minimize horsepower loss due to elevation and lower air density. At high elevations turbochargers compress more air into the engine cylinders making up for the lower air density allowing the engine to produce power as if it was at sea level. This extra tunability is found only in turbocharged applications.
This ^ but always quote your sources!! :p
https://www.garrettmotion.com/news/...at-elevation-counteracting-lower-air-density/

TLDR: Difference in air compensation (% oxygen) at altitude is negligible, so as long as the turbo can handle the increased RPMs required to pump the lower density air to the same boost pressure, then the engine will compensate and produce the same power produced at sea level.

No, A turbocharged engine will not make the same power at altitude as at sea level without turning the boost higher. The website linked is being misunderstood here. Read it again, it says and shows in the chart that you have to increase the boost to maintain the same power at altitude.

As to the why;

Everyone seems to be good with losing power due to less O2 being available per volume of air, so moving on to boost. Boost is not an absolute quantity, it is the restriction faced by cramming air into an engine. It is relative to the outside pressure (PSI, pounds per square inch ). Boost gauges show the pressure above the ambient outside pressure and is read as pounds per square inch gauge, or PSIG). For example. at sea level (close enough) you are looking at 14.7 lbs of pressure per square inch. If your turbo shows 18lbs of 'boost' at sea level it is really looking at 32.7 PSI of real pressure as it uses ambient pressure as a zero point, while showing only 18 PSIG on the gauge.

As you go up in altitude the density of air drops (not as much air above it pushing down as there is at sea level.) About 83% of sea level air density is in Denver at a mile high, so normally aspirated engine loses 17% of its power. So instead of 14.7 PSI, they start off at 11.8 PSI, that means the same 18 lbs of boost (18 PSIG) is only pushing air into the engine at a real 29.8 PSI. Looking at the sea level example of 32.7 PSI and the Denver 29.8 PSI, you can divide 29.8/32.7 and get 91% of the same density is being forced into the engine at altitude. So you lose power, just not as much as a normally aspirated engine (about a third of the loss for a normally aspirated engine in real life). You can make up the difference, but you would have to change the settings to increase boost (PSIG) by 3 PSI or so, ignoring the compressor map heat gain and efficiency changes.

The same physics will cause a turbo to spool slower, raise the RPM and load required to get to full boost, etc. when at altitude. The lower the boost, the closer the power loss gets to a normally aspirated engine. If you were running a diesel with 40 PSIG, you would not notice much difference at all. (95% as much density crammed in), if you ran 1 PSI, it would be almost the same as no turbo at all, which makes sense.
 

BDSteelies

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No, A turbocharged engine will not make the same power at altitude as at sea level without turning the boost higher. The website linked is being misunderstood here. Read it again, it says and shows in the chart that you have to increase the boost to maintain the same power at altitude.

As to the why;

Everyone seems to be good with losing power due to less O2 being available per volume of air, so moving on to boost. Boost is not an absolute quantity, it is the restriction faced by cramming air into an engine. It is relative to the outside pressure (PSI, pounds per square inch ). Boost gauges show the pressure above the ambient outside pressure and is read as pounds per square inch gauge, or PSIG). For example. at sea level (close enough) you are looking at 14.7 lbs of pressure per square inch. If your turbo shows 18lbs of 'boost' at sea level it is really looking at 32.7 PSI of real pressure as it uses ambient pressure as a zero point, while showing only 18 PSIG on the gauge.

As you go up in altitude the density of air drops (not as much air above it pushing down as there is at sea level.) About 83% of sea level air density is in Denver at a mile high, so normally aspirated engine loses 17% of its power. So instead of 14.7 PSI, they start off at 11.8 PSI, that means the same 18 lbs of boost (18 PSIG) is only pushing air into the engine at a real 29.8 PSI. Looking at the sea level example of 32.7 PSI and the Denver 29.8 PSI, you can divide 29.8/32.7 and get 91% of the same density is being forced into the engine at altitude. So you lose power, just not as much as a normally aspirated engine (about a third of the loss for a normally aspirated engine). You can make up the difference, but you would have to change the settings to increase boost (PSIG) by 3 PSI or so, ignoring the compressor map heat gain and efficiency changes.

The same physics will cause a turbo to spool slower, raise the RPM and load required to get to full boost, etc. when at altitude. The lower the boost, the closer the power loss gets to a normally aspirated engine. If you were running a diesel with 40 PSIG, you would not notice much difference at all. (95% as much density crammed in), if you ran 1 PSI, it would be almost the same as no turbo at all, which makes sense.
I'm not so sure about that. Do you have more details on how the turbo boost gage operates? Does the ECU always "zero out" the boost gage to ambient pressure at startup or during operation?

As I understand it - 18 psig of boost is 18 psig, regardless of elevation or atmospheric pressure. At 18 psig at the outlet of the compressor, assuming temperature and air composition is constant, you will have the same molecular weight (mass flow) of oxygen regardless of the ambient air density. The turbo will just need to spin faster and/or reduce bypass to hit 18 psig at the compressor.

On paper that would mean the same horsepower regardless of ambient pressure. In reality I'm sure turbo efficiency at different compressor tip speeds and turbo lag plays a big role in the actual power and acceleration at elevation.
 
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BDSteelies

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Educated myself a bit more on this - the MAP (manifold absolute pressure) sensor is what the ECU uses to sense boost pressure and control fueling. So at higher elevations, the turbo will work harder (higher pressure ratio) to compensate for the lower ambient pressure and generate the same manifold pressure that the engine requires. Assuming you don't exceed set limits of the turbo, power loss is the result of running the turbo outside of ideal operating conditions, and not due to reduced manifold pressure.

What I'm still not sure about is if the instrument cluster boost "gage pressure" on the Bronco is truly showing gage pressure. Does it measure and subtract actual ambient pressure in real time? Or does it just offset a preset sea level pressure from the MAP sensor's absolute pressure? If the former, boost pressure would read higher at higher elevations for a given power level. If the latter, boost pressure would be consistent.
 

indio22

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P.S. If anyone has some opinions of CO Springs, I'm all ears. That's taking it way off topic, but oh well. I've visited before, but not for any meaningful amount of time.
Back in the 90's I lived a couple hours north in Fort Collins. Colorado Springs was known for Christian fundamentalism. Focus On The Family and other such groups located there. I don't know how much sway they have these days, but something to think about depending on your persuasion. Anyway lots of outdoor activities along the front range, you'll have a blast with a Bronco in Colorado.
 

paxfish

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I can tell you my 3.5 EB is a monster in the Rockies. I suspect the turbos have more capacity than is normally used, and the excess is bled off. Up here, perhaps the wastegates don't open quite as early...

With regard to living up here (9,100ft, Summit County), figure out your activities, and live close to them. Driving up from the Front Range every weekend is a PITA!
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