Calculating engine parameters from power requirement

  • #1

Main Question or Discussion Point

Hi,
I've defined engine power requirements based on driving dynamics, but am not sure how to extend this to engine parameters. From design requirements, I've fixed my gear ratios, and hence can determine how much power and torque is required from the engine at a particular speed.
I want to then determine the architecture of the engine, in terms of bore, stroke, compression ratio, amount of fuel injected, as values that I can tune. Since its an SI engine, I'm taking air fuel ratio as stoichiometric, but I'm still unable to figure out how to determine the engine parameters as a function of the power required ?
Thanks in advance.
 

Answers and Replies

  • #4
rcgldr
Homework Helper
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As a general rule, most engines with 4 valves per cylinder will produce about 65 to 85 ft-lbs per liter. The 85 ft-lb figure is common for performance motorcycles and high end exotic type cars. For a mid-range example, a 2015 Genesis 5.0 normally aspirated v8 has a 5.038 liter engine, produces 383 ft lb of torque for 76 ft lbs per liter at 5000 rpm, and it produces 420 hp at 6000 rpm. The power is an issue of how high the rpm is at peak power. For a high end example, Kawasaki ZX14R motorcycle, 1.441 liter engine, 120 ft lb of torque at 7600 rpm for 83.3 ft lb torque per liter, and produces 197 hp at 10,000 rpm.
 
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  • #5
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If you want to see the "performance envelope" it's easier to use the torque curve. The power curve produces different acceleration rates in each gear, and acceleration rate per unit power declines as engine rpm and/or drive wheel rpm increases. Note that drive wheel power is the same as engine power less driveline losses regardless of gear ratio.
 

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