A friend who lives in Denver and I were discussing the effects of altitude on the performance of his car. I didn’t understand much of what he theorized about the air pressure and the fuel injection system and hope someone hear can help.
Allegedly HP is less (20%?) at high altitude but (and here’s where I get confused), fuel consumption is lessened as well.
Can anyone illuminate me in layman’s terms how this could be. It seems to me that the engine would have to work 20% harder to achieve the same results as at sea-level and fuel consumption would be a wash.
I would have thought that you would get less power but greater economy since the mix would have to be “leaned” like on a plane to prevent the engine running too rich. This would mean you are using less fuel to compensate for the thinner air.
That’s the thing, it can’t achieve the same results as at sea level. You can’t make up for that lost power by working the engine harder.
You are producing 20% less power. Since how much fuel you burn is related to how much power you are producing, you are also now using 20% less fuel. The effect is almost exactly the same as if someone had rigged your throttle for something less than full travel. The trade-off, of course, is less performance.
Gas and air burn at a ratio of about 14.7:1 by weight.
Now think of the engine as an air pump. The more air (oxygen) you put through the engine, the more fuel you can add and the more power you can produce. Increasing one (air or fuel) without increasing the other will not produce any more power.
Now subtract some air (in this case due to altitude) you then have to also subtract some fuel to maintain the 14.7:1 ratio that the engine wants.
However once you start driving this whole discussion goes kinda upside down. Let’s say I normally press the accelerator pedal 20% (at sea level) to achieve what I consider to be satisfactory acceleration from a stop light. To get that same acceleration I will be pressing the accelerator about 40% in Denver. So Berkut is incorrect. Unless you are at or near wide open throttle, lost performance can be recaptured by open the throttle more. Opening the throttle more brings in more air witch causes more fuel to be injected.
furthermore there is another problem with high altitude fuel mileage. At high altiude there are mountains. Yeah I know this is a BGO* but going up a mountain really plays hell with your average fuel mileage.
No, it’s not incorrect. To produce x amount of power in Denver will take the same amount of fuel as it does to produce x amount of power at sea level. Your engine is not working any harder to produce that x amount of power. You can increase the throttle to compensate for the drop in manifold pressure, but you are not working the engine any harder.
BTW, I agree with your post, but I think you misunderstood what I was saying. When I spoke of power that can’t be made up, I was referring to how an engine that produces 100hp at sea level will produce a lot less in Denver. The point I was trying to (perhaps unclearly) make was that you can’t get back to that 100hp by working the engine harder. You just don’t have the air to do it.
I think were the confusion lies with the use of the word harder. Most people equate opening the throttle further as working the engine harder.
I agree with you that a normally aspirated engine that produces 100HP at sea level will produce less in Denver, and short of modifying the engine you are not going to recapture it.
