DaveInDaytona
05-21-2003, 06:52 AM
Did you ever look at dyno sheets and notice the STD or SAE designation ? Did you ever wonder what that was all about ?
OK, maybe you're not all as strange as me, but this is a good explanation for the motor freeks out there that were curiuos, or are not curious because you saw this.
See if this makes sense.........
The power output of an internal combustion engine is significantly influenced by barometric pressure, ambient air temperature, and air humidity.
The lower ambient barometric pressure reduces the density of the air, thus reduces the amount of oxygen filling the cylinder for each cycle, resulting in lower power output. Conversely, higher barometric pressure increases power.
The lower ambient air temperature results in increased density of the air, thus increases the amount of oxygen filling the cylinder for each cycle, resulting in higher power output. Conversely, higher air temperature reduces power output.
Lower air humidity (= less water vapor) leaves more room for oxygen per cubic foot of air, thus increases the amount of oxygen filling the cylinder for each cycle, resulting in higher power output. Conversely, higher air humidity reduces power output.
Several Standards organizations have determined methods for estimating engine power under reference conditions. The best known organizations are:
ISO (International Standards Organization), worldwide
SAE (Society of Automotive Engineers), USA
ECE (European Community), Europe
JIS (Japanese Institute for Standardization), Japan
DIN (Deutsche Industrie Norm), Germany
There are power correction standards for gasoline and Diesel engines, for applications in road vehicles, stationary engines, or marine engines, etc. For a motorcycle dynamometer, relevant standards are those generally intended for gasoline engines in road vehicles and those specific to motorcycles.
SAE -- The SAE standard applied is a modified version of the SAE J1349 standard of June 1990. Power is corrected to reference conditions of 29.23 InHg (99 kPa) of dry air and 77 F (25°C). This SAE standard requires a correction for friction torque. Friction torque can be determined by measurements on special motoring dynamometers (which is only practical in research environments) or can be estimated. When estimates must be used, the SAE standard uses a default Mechanical Efficiency (ME) value of 85%. This is approximately correct at peak torque but not at other engine operating speeds. Some dynamometer systems use the SAE correction factor for atmospheric conditions but do not take mechanical efficiency into consideration at all (i.e. they assume a ME of 100%). Some use a more sophisticated algorithm for calculating friction torque, based on a summary of thousands of friction power tests performed by the automotive industry. This proprietary algorithm estimates friction torque as a function of piston speed and engine displacement.
The "SAE corrected" power numbers indicated by the dynos are more accurate estimates of engine power output under reference conditions and use either a calculated ME correction or use a fixed ME of 85%.
Make sense ?
OK, maybe you're not all as strange as me, but this is a good explanation for the motor freeks out there that were curiuos, or are not curious because you saw this.
See if this makes sense.........
The power output of an internal combustion engine is significantly influenced by barometric pressure, ambient air temperature, and air humidity.
The lower ambient barometric pressure reduces the density of the air, thus reduces the amount of oxygen filling the cylinder for each cycle, resulting in lower power output. Conversely, higher barometric pressure increases power.
The lower ambient air temperature results in increased density of the air, thus increases the amount of oxygen filling the cylinder for each cycle, resulting in higher power output. Conversely, higher air temperature reduces power output.
Lower air humidity (= less water vapor) leaves more room for oxygen per cubic foot of air, thus increases the amount of oxygen filling the cylinder for each cycle, resulting in higher power output. Conversely, higher air humidity reduces power output.
Several Standards organizations have determined methods for estimating engine power under reference conditions. The best known organizations are:
ISO (International Standards Organization), worldwide
SAE (Society of Automotive Engineers), USA
ECE (European Community), Europe
JIS (Japanese Institute for Standardization), Japan
DIN (Deutsche Industrie Norm), Germany
There are power correction standards for gasoline and Diesel engines, for applications in road vehicles, stationary engines, or marine engines, etc. For a motorcycle dynamometer, relevant standards are those generally intended for gasoline engines in road vehicles and those specific to motorcycles.
SAE -- The SAE standard applied is a modified version of the SAE J1349 standard of June 1990. Power is corrected to reference conditions of 29.23 InHg (99 kPa) of dry air and 77 F (25°C). This SAE standard requires a correction for friction torque. Friction torque can be determined by measurements on special motoring dynamometers (which is only practical in research environments) or can be estimated. When estimates must be used, the SAE standard uses a default Mechanical Efficiency (ME) value of 85%. This is approximately correct at peak torque but not at other engine operating speeds. Some dynamometer systems use the SAE correction factor for atmospheric conditions but do not take mechanical efficiency into consideration at all (i.e. they assume a ME of 100%). Some use a more sophisticated algorithm for calculating friction torque, based on a summary of thousands of friction power tests performed by the automotive industry. This proprietary algorithm estimates friction torque as a function of piston speed and engine displacement.
The "SAE corrected" power numbers indicated by the dynos are more accurate estimates of engine power output under reference conditions and use either a calculated ME correction or use a fixed ME of 85%.
Make sense ?