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Old 09-15-2017, 06:08 AM   #21
mfifield01
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There are some caveats. I read a few years ago that Cummins will make the same HP up to 10,000'. I've seen Ecoboost issues reported at altitude. The turbo has to work more to keep the same PSI. In real world tests, the Hemi (5.7l) has done as good or better at altitude vs the Ecoboost.

From personal experience, I had a Silverado (5.3l) rental truck in Denver. That thing was struggling to climb. It was so bad, I even popped the hood to check what engine was under it. I thought it had the smaller V8.
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Old 09-16-2017, 09:54 AM   #22
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In real world tests, the Hemi (5.7l) has done as good or better at altitude vs the Ecoboost..
LOL! Ummm, no. I prove this wrong on a daily basis.



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Old 09-16-2017, 01:07 PM   #23
Outback 325BH
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Originally Posted by mfifield01 View Post
In real world tests, the Hemi (5.7l) has done as good or better at altitude vs the Ecoboost.

Only in fantasy land.



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Old 09-16-2017, 01:13 PM   #24
mfifield01
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The test was in 2013, so it's most likely the inferior transmission (gearing) of the F150. The 8-speed of Ram has better gearing.

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Old 09-16-2017, 01:46 PM   #25
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I pass them up every mountain. T

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Old 09-19-2017, 08:28 AM   #26
Desert185
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Originally Posted by Outback 325BH View Post
Higher altitude the air is thinner (less oxygen per volume).

Computer controlled engines automatically adjust the fuel/air mixture so you are always running at stoich -- not lean and not rich.

This means less fuel used at altitude.

However, less fuel and air per volume means less power your engine is producing. This means you will often have to push the pedal down more and/or downshift and/or run your engine at a higher RPM to do any given the task at altitude vs lower altitude.

Turbocharged/supercharged engines don't have this problem because the charger force-feeds the engine and can always maintain the ideal amount of density of air/fuel in the cylinders.

A lot of factors to determine actual mileage ramifications.


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That's it, although, my turbocharged vehicles always do better power-wise when close to sea level and better mileage-wise when at higher elevations. The right pedal controls power and fuel flow.
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Old 09-19-2017, 12:46 PM   #27
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Think of it this way, at 10,000 feet, your hemi only puts down 65-70% of rated HP (thats' off the top of my head). So essentially, you're taking it "easier" on the gas.

In theory, your hemi is capable of the exact same mileage at sea level as it is at 10,000ft elevation, but you'd need to reduce your "foot"...



Pilots of non-turbo aircraft have to be aware and "compensate" for the fact that our airplanes have different fuel usage (less fuel at throttle setting) and have radically different takeoff performance since motors are making a fraction of full power. I've got a table somewhere that tells me altitude, % of power output, and how much longer take-off will take a altitude. Same thing happens in naturally aspirated trucks.

Yes, turbos compensate for altitude. An ecoboost should kill a hemi on a dyno at 10,000 feet.
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