Calculate Efficiency with MPG and other things

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SUMMARY

The discussion focuses on calculating engine efficiency using parameters such as RPM, MPH, MPG, and BTU content. The user seeks to derive an efficiency percentage based solely on these variables, acknowledging the complexity due to factors like throttle position affecting power output. The consensus suggests that while theoretical calculations can be made, the most accurate method involves using a dynamometer to create a performance map for the engine. This approach allows for a comprehensive understanding of efficiency across varying conditions.

PREREQUISITES
  • Understanding of engine performance metrics, including RPM and horsepower.
  • Familiarity with fuel consumption measurements, specifically MPG.
  • Knowledge of energy content in fuels, particularly BTU calculations.
  • Experience with dynamometer testing and performance mapping techniques.
NEXT STEPS
  • Research methods for calculating engine efficiency using BTU and MPG data.
  • Learn about the operation and setup of a dynamometer for performance testing.
  • Explore the impact of throttle position on engine power output and efficiency.
  • Investigate the creation of performance maps for various engine types.
USEFUL FOR

Automotive engineers, performance tuners, and anyone involved in optimizing engine efficiency and understanding fuel consumption dynamics.

ISX
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My engine has a data plate stating it uses x amount of fuel to make x amount of power at x RPM. I can use that to derive the efficiency but then all other calculations I use, such as finding the HP at a given load using the fuel amount I get with MPG at a given speed, are all derived from that ONE efficiency. I know that is completely wrong but I have no other way to do it given the needed variables.

My question is, is it possible to derive an efficiency % using just RPM/MPH/MPG/BTU content...? I have a general idea of the truck weight (6500lb) but the more I think about it the more I think all you would need is BTU/MPG/and maybe speed. It seems energy used (in BTU content x gallons burned) to go a certain distance would tell you work done. But I have no clue. What do you guys think?
 
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This is very difficult. The engine efficiency and power depend on throttle position, so they can vary even at constant rpm. Putting the truck on a dyno and creating a performance map is the only way I can think of to do this.
 

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