Running at altitude?

[Crazyboat]

How much if any "Noticeable" difference is there when running the same engine at sea level vs. 1,000', 2,000, 3,000 etc?

 

[KMixson]

A 3000 foot difference might not be that noticeable. Now if you are running at a 10,000 foot difference you might see a difference. Back when I was younger I took a car up to Mt. Evans in Colorado. In Denver the car ran fine. After going up that mountain in the car it started skipping and running rough probably around 12,000 feet. This was back when cars had carburetors on them. The mixture was a little off for the altitude encountered and the low oxygen percentage of the air. After walking to the top of the mountain even I was huffing and puffing trying to get enough oxygen especially being from sea level. That was a 14,000 foot difference for me. This is why a lot of light aircraft have mixture controls on them along with the throttle.

 

[.Mike]

The rule of thumb that I have read is 3% reduction in horsepower for every 1,000 ft in altitude.

Sea Level - 10hp
1,000 - 9.7hp
2,000 - 9.4hp
3,000 - 9.1hp
4,000 - 8.8hp
5,000 - 8.5hp
6,000 - 8.2hp

...etc.

I'm sure the differences could be measured, but not sure where someone would notice a difference.

 

[Crazyboat]

The rule of thumb that I have read is 3% reduction in horsepower for every 1,000 ft in altitude.

Sea Level - 10hp
1,000 - 9.7hp
2,000 - 9.4hp
3,000 - 9.1hp
4,000 - 8.8hp
5,000 - 8.5hp
6,000 - 8.2hp

...etc.

I'm sure the differences could be measured, but not sure where someone would notice a difference.

Assuming these numbers are close, I doubt anyone would notice much on anything below 4,000 ft. Thanks!