Elevation mpg increase?

[Phase]

Are there are numbers for how much your mpg increases at higher altitude?

Like 2 percent every 1000 feet?

How much better mpg do you get at 7000 feet versus sea level? Wondering if there are any hard numbers

[freebeard]

I can see how a Mass Airflow Sensor might compensate, but don't Bonneville (4,219ft) racers struggle when they go to the salt flat in Bolivia (~12,000ft)?

https://en.wikipedia.org › wiki › Salar_de_Uyuni
Salar de Uyuni - Wikipedia
Salar de Uyuni (or "Salar de Tunupa") [1] is the world's largest salt flat, or playa, at over 10,000 square kilometres (3,900 sq mi) in area. [2] It is in the Daniel Campos Province in Potosí in southwest Bolivia, near the crest of the Andes at an elevation of 3,656 m (11,995 ft) above sea level.

[redpoint5]

Too many variables, but it does seem like enough data would produce some rule of thumb.

The reduced air density means aerodynamic drag is reduced, and the reduced density is also like having a warm air intake, meaning the throttle will be open more for any given engine load, which reduces pumping losses.

[oil pan 4]

My worst mpg ever was up around 7,000 to 9,000 feet.
Diesels definitely get worse mpg.

[redpoint5]

Originally Posted by oil pan 4

My worst mpg ever was up around 7,000 to 9,000 feet.
Diesels definitely get worse mpg.

No turbo?

I don't know the MPG on 450cc dirt bikes with a carb at 14,000 ft, but power fell off a cliff.

Most modern vehicles will get better MPG though.

[freebeard]

Most modern vehicles will get better MPG though.

How and why?

[redpoint5]

Originally Posted by freebeard

How and why?

Explained above. Throttle by wire combined with O2 sensors and MAP/MAF sensors means the car adjusts fueling rate to compensate for the reduced air density.

Carbs don't compensate. They are calibrated for a particular air density and do not change.

Diesels should get better fuel economy due to reduced aerodynamic drag so long as the turbo is feeding enough air to burn all the fuel. If it's rollin coal, then it's wasting fuel.

[freebeard]

Too many variables, but it does seem like enough data would produce some rule of thumb.

This part?

I mentioned airflow sensors. Carbs got turbochargers in WWII to compensate for altitude.

The rule of thumb would pit ICE efficiency against aerodynamic drag.

[Phase]

i was just asking how much drag is reduced due to air density. i know theres less oxygen too and that usually translates to less gas burned from random things ive read online too

[redpoint5]

Originally Posted by Phase

i was just asking how much drag is reduced due to air density. i know theres less oxygen too and that usually translates to less gas burned from random things ive read online too

I believe drag is proportional to density (someone correct me if I'm wrong).

This density calculator can give air density at any given elevation and temperature.

https://www.mide.com/air-pressure-at...ude-calculator

I used 1 ATM (sea level) and found that at 10,000ft density is 0.69 ATM.

I expect a 30% reduction in aerodynamic drag at 10,000 ft.

Regarding gasoline consumption in a modern vehicle; it's proportional to the amount of power needed. It takes the same amount of fuel to produce 50 horsepower regardless of elevation. The only thing the elevation does is require a wider throttle opening for any given horsepower compared with sea level, but the fuel consumed for that given horsepower is the same. The only time elevation becomes a limiting factor is at wide open throttle. You will generate more peak power at sea level than at elevation.