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ORIGINAL: hydrashocker
I've taken my truck up to 10,000 feet and can still smoke em. That is not relevant. Your truck automaticly adjusts the intake flow of fuel and air.
Where did you get your Fact Book?
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Where did you get your facts? Altitude plays a part in calculating true horsepower. The air is thinner at higher altitudes, and no matter how the engine controls adjust for that, there is loss of horsepower do to thin air, (less air).
Air/Fuel Ratio - The ratio of pounds of Air to pounds of Fuel needed for combustion in an engine. Air/Fuel ratio is based on pounds of AIR to pounds of FUEL but carbs are metered (jetted) by volume so changes in fuel can change A/F ratios. A/F Ratios range from about 2:1 for NitroMethane to about 16:1 for gasoline, with 14.7:1 considered the stoichiometric or chemically correct ratio under perfect conditions with normal (non-oxygenated) gasoline. Gasoline A/F ratios for best power tend to be in the 13.25:1 - 13.75:1 range.
Sub-stratospheric conditions above 10,000 ft., robs your engine's power output a full 34 %, due to a combination of lowered oxygen levels, and a significant reduction in atmospheric pressure values at altitude.
Oxygen tends to settle to low places, due to atomic weight molecular theories and gravity. Oxygen levels found at 5,000 ft. are a full 14% less than levels found at sea-level. At 10,000 ft. this percentage loss of oxygen now approaches 30%. Hold on though, you are about to discover the second power robbing aspect associated with high altitude engine operations.
Atmospheric pressure that we too often underestimate. Its easy to do, most Americans live at elevations below 500 ft. and are essentially at sea level. This is our normal condition to live and breathe in deep, rich, heavy air. Atmosphere pressure is proportional to the weight of all the above molecules resting and pressing down to the bottom from miles above. Remember diving to the bottom of a swimming pool, how with increasing depths, the extra water pressure hurts your ears. Atmospheric pressure is alot like the collective height / weight of the water molecules, but instead we are talking about air molecules. We are quite accustomed to life at the bottom, under the weight of miles of air molecules that are stacked above you. Now consider the opposite, we will experience the absence of the two miles of air molecules, the ones we left behind and below us in Eastern Kansas. Air pressure differentials are what lifts a hot air balloon and its heavy gondola off the ground. Ever hear about Colorado Rockies home-run advantages with thin air at Coors Stadium. Baseball statisticians add an asterick to the batter's home-run numbers for runs hit in Denver.
Returning to the situation back underneath our hoods. It follows then that less of air molecules resting and pressing above our throttle plates at 10,000 ft. will fill our motor's cylinders less effectively when the piston travels down. Furthermore, this slower fill rate is now at odds with the sea-level designed camshaft timing values. The mechanical time the valves are open will remain the same, yet due to the reduced atmospheric pressure, far less mixture will enter the cylinders. Clearly this will remain the key power robbing component that we will be least able to compensate for with adjustments. Two-stroke motors use ports in the cylinder wall to time air flows and these ports are the equivalent of the 4- stroke's camshaft. The two-stroke is so dependant on heavy sea-level pressure differentials, that at altitude, intake, transfer, and exhaust back pressures, will be disproportionately disrupted, robbing the two stroke motor of greater torque than 4-stroke motors.
Durango burnout.
