The Effect of Altitude on a Car or Truck Engine
Internal combustion engines (those which must burn something in order to produce power) are brilliantly engineered machines. However, they have one serious shortcoming — they lose power at higher altitudes. Drive your family car, minivan, or truck into the mountains and you will notice its performance becomes sluggish, lethargic, and downright wimpy. In most cases it is not bad fuel, poor maintenance, or the heavy load. Instead, the culprit is the altitude — the elevation above sea level.
WHY IS POWER LOST, AND HOW MUCH DOES IT DECREASE?
As altitude increases, air becomes thinner. As air is required for combustion, and there is less available at higher altitudes, the engine makes less power. In general, a naturally aspirated engine will lose about 3 percent of its rated power for every 1,000 feet of altitude gained. Remember that 2013 Lexus GS350 F Sport that we reviewed last month? At sea level, its 3.5-liter V6 is making about 306 horsepower. Drive it up to Big Bear Lake in the San Bernardino Mountains (elevation 6,750 feet) and the engine will have lost 20 percent of its power — down to just 245 horsepower! Drive it up to the Tioga Pass (elevation 9,960 feet) en route to Yosemite Valley and it will have lost about 30 percent of its power — down to just 215 horsepower! Even at the Rose Bowl (elevation 830 feet), the Lexus is down to 299 horsepower. Even small power losses are often noticeable, especially when the vehicle is loaded or while towing.
DOES TURBOCHARGING HELP?
Yes, forced induction (turbocharging and supercharging) does help. In each of these applications the air is forced into the engine at higher pressures, effectively negating some of the loss from altitude. However, turbocharged (and supercharged) engines still lose about 1.5 percent of their power for every 1,000 feet of altitude gained. Private pilots who read the site will correctly state that turbochargers are very effective at reducing power loss at higher altitudes, but aircraft engines are specifically designed to work best at cruising levels — not sea level, as are passenger vehicles.
ARE ANY VEHICLES IMMUNE FROM THE EFFECTS OF ALTITUDE?
Interestingly enough, electric vehicles (powered by batteries and electric motors) are nearly immune to power losses due to altitudes. While some may not run as strongly at higher elevations, most of those issues are cooling related as the vehicle’s software may simply reduce power to keep temperatures low as heat transfer is less effective at altitude — but that’s an article for another day.
– Michael Harley