Gary RV_Wizard
Site Team
Traditional wisdom is that the performance of a "normally aspirated" internal combustion engine decreases about 3% for every thousand feet of altitude, because of the decrease in the density of the air. That was a good number in the past, but I believe it no longer applies to any modern vehicle engine. My reasoning is that no modern engine (in the USA anyway) is "normally aspirated" within the meaning of this venerable rule of thumb. First, of course, is the fact that many modern engines have turbo chargers or even superchargers and are not in any sense "normally aspiraed". Turbo charged engines get all the air they need rammed into them by the turbocharger. But second, even non-turbocharged modern engines still have their air/fuel mixture managed quite ridgidly by an engine control computer that measures the density if the incoming air charge and adjusts the air/fuel mix accodingly. To meet fuel economy and emissions goals, the air/fuel mix is always kept at it stoichiometric value, which is 14.7:1 (air-to-fuel) for gasoline. This ratio is maintained at any altitude and any temperature within the vehicle's designed operating range. If the density of the air decreases, the control system increases the amount of air in the air/fuel charge until there is sufficient oxygen for a proper fuel burn, i.e. a 14.:1 ratio. Even if the control system misreads the air density, feedback from the oxygen sensor in the exhaust will tell it if the mix was too lean or too rich and it will further adjust until the fuel is burned fully, yielding optimum power as well as minimal pollutants.
I don't know just how much altitude the various engine designers planned for (or that the EPA requires), but you can bet that it is at least 10,000 feet because many regions in the USA are 5000 feet and above. I just spent several days in Montana and Wyoming without ever coming below 6500 feet.
Given this, in my opinion there is no longer any reason to allow for any decreased engine performance at the sort of altitudes an RVer may encounter.
Comments, anyone? ???
I don't know just how much altitude the various engine designers planned for (or that the EPA requires), but you can bet that it is at least 10,000 feet because many regions in the USA are 5000 feet and above. I just spent several days in Montana and Wyoming without ever coming below 6500 feet.
Given this, in my opinion there is no longer any reason to allow for any decreased engine performance at the sort of altitudes an RVer may encounter.
Comments, anyone? ???