If you have moved from low elevation to the mountains, you've probably noticed that your car, SUV, or pickup doesn't get up and go like she used to. This is due to the decreased air density at high elevations.
Vehicle engines need, among other things, oxygen and fuel (typically gas or diesel) to operate. The amount of fuel your vehicle can burn is relative to the amount of oxygen it can get. At higher elevations, the decreased air density means there is not as much oxygen in a volume of air. Because of this, your vehicle cannot burn as much fuel, therefore it can't make as much power as it does at lower elevations. It has to work harder (run higher RPM's) to make power compared to low elevation.
This used to be a HUGE problem for cars before the days of computerized fuel injection. The engines of that time period did not adequately reduce fuel flow at high altitude, so they would run rich and would put out a lot of smoke. People that moved to the mountains would have to have their carburators modified (re-jetted) to operate consistently at high altitude.
Today, the computer modules and sensors that control our engines can correctly adjust fuel flow based on air density. BUT, fuel flow is still lower than it was at low altitude, hence the power loss.
How do you solve this problem? TURBOCHARGING is the answer. Vehicles with turbocharged engines compress incoming air. The compressed air contains much more oxygen per volume than a non-turbocharged engine can take in.
This means that if you were lucky enough to already have a turbocharged vehicle when you moved to the mountains, then this talk of losing power at altitude makes no sense to you. Your car hasn't lost any power, has it?
The technical details: Most turbocharging systems produced since the mid-1980's are able to adequately increase "boost" at higher elevations to account for lower air density, helping to maintain a constant absolute pressure in the engine. They do this by holding the Waste Gate closed longer at high elevations than they do at low elevations. At low engine RPM's, you may still notice slight power loss because the turbo is not able to spool enough to fully compensate for the low air density, but once engine speed increases a little, power loss will disappear.
Between my wife and myself, we have 3 vehicles. After moving to the mountains, we traded in one of them for a turbo diesel. Now, we wish all of our vehicles were turbo diesels. There is just no equal to a turbo diesel in the mountains.