This paper will address the affects of how higher altitudes affect the horsepower output of automotive vehicles as well as things you can do to compensate for this phenomenon. As many people are relocating to the state of Colorado, this subject has become a common of discussion among new residents and the automotive service industry. Altitude has a very significant affect on vehicle horsepower and is often misunderstood by vehicle owners. Some owners are told that their vehicles will lose up to 20% horsepower by being in Colorado, but there is much more to the story than a simple statement like that. Let’s explore some simple facts about the affect of altitude on horsepower. It is best to have access to a calculator to complete this activity. Many cell phones has built in calculators for easy access. We will use some common automotive mathematical formulas to calculate “theoretical performance” values.
Our case study vehicle will be a Ford with a 5.4L (330 CID). The first learning objective will be how to convert liters to cubic inches. The easiest method to do this is to multiply liters (5.4) by 61.024. (5.4 x 61.024 = 329.53) Most manufacturers will “round up” to the nearest number, so 329.53 would become 330 cubic inches. Our example vehicle specifications indicate that it delivers about 300 HP and 365 lb ft of torque. These specifications are the result of engineering testing and measurements. These values are determined by using a Society of Automotive Engineers (SAE) correction factor to keep horsepower and torque publications standard and consistent. The engineered calculations and measurements are factored and corrected to sea level and are often referred to as “sea level performance”.
With the example vehicle generating 300HP at sea level, if we use the following formula to correct for changes in altitude, we can calculate the theoretical power loss at any altitude. (HP x Altitude [in feet] divided by 1,000), then multiplying the answer by 0.03. Then, subtract that answer from the stated vehicle horsepower. The total formula would be written as:
(HP X Altitude [in feet] / 1,000 X 0.03 – HP)
Let’s work with the example of the Ford vehicle using this formula. The altitude of Colorado Springs, CO is about 6,000 feet. The formula with actual values inserted would look like this: (300 X 6,000 / 1,000 X 0.03 – 300) 300HP times 6,000 equals 1,800,000. Then, 1,800,000 divided by 1,000 equals 1800. Then, 1800 multiplied by 0.03 equals 54 (horsepower). 54 horsepower subtracted from 300 equals 246, which is the new theoretical vehicle horsepower at an altitude of 6,000 feet. Now, calculate the vehicle horsepower at a new altitude of 8,000 feet.
These calculations do not include major influencing factors such as ambient temperature or vapor pressure and are used just for a reference. The manufacturers and the aftermarket industry use ambient air temperature and vapor pressure in their horsepower gain calculations for their “add-on” performance products to determine the added horsepower gain. If you want to try and compensate the loss of horsepower of your engine by installing aftermarket parts that are designed to enhance engine performance, you would use the same formula. Let’s say that you wish to install a cold air intake system on your vehicle and the advertised specifications say that it will add 12 HP to your vehicle. We must use the same altitude correction formula to determine the actual gain for vehicle operation in Colorado. (12HP X 6,000 / 1,000 X 0.03 – 12) = 9.84HP now, adding the 9.84HP gain to the original 246HP gives you a total of 255.84HP (theoretical) for your vehicle.
You can continue to calculate the horsepower gain for aftermarket products until you find a combination of products that will bring your vehicle horsepower back to sea level specifications for the altitude your vehicle operates at. In the example of the Ford vehicle in this document, we would have to find products that would increase the horsepower of the 5.4L engine to about 370HP at sea level to obtain the factory 300HP at 6,000 feet above sea level. Have fun!!!