Piston Force Graphs: Manipulating Parameters in Combustion Pistons

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Discussion Overview

The discussion revolves around the manipulation of parameters affecting piston force in combustion engines, specifically focusing on how these parameters influence graphs of piston force versus displacement or time. Participants explore various factors such as fuel amount, air amount, piston geometry, and engine RPM.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant inquires about the availability of graphs depicting piston force in relation to displacement or time, emphasizing interest in how different parameters affect these graphs.
  • Another participant shares links to external resources that may provide relevant information on performance and operating characteristics of internal combustion engines.
  • A participant discusses the dynamics of piston force, noting that the highest force occurs at top dead center (TDC) in the overlap position, and mentions the impact of piston weight on RPM capabilities.
  • There is a mention of the relationship between rod ratio and engine performance, with some arguing that lighter pistons allow for higher RPMs, while others suggest that a longer rod ratio may yield more power.
  • A participant references previous discussions on a different forum regarding piston force, suggesting that there are numerous threads available for further exploration of the topic.

Areas of Agreement / Disagreement

Participants express varying opinions on the effects of piston weight and rod ratios on engine performance, indicating that multiple competing views remain without a clear consensus.

Contextual Notes

Some claims made regarding the relationships between piston weight, rod ratios, and engine performance are based on assumptions that may not be universally accepted or validated. The discussion also references external resources that may contain additional, but unverified, information.

physea
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Hello guys!
Can I view graphs of Piston Force versus Piston Displacement or time, in a combustion piston?
I would be interested to see how the graph varies by manipulating parameters such as fuel amount, air amount, piston geometry, rpm, etc
Thanks!
 
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hmm I can tell you that the highest force on the piston is at tdc in the overlap position. The less the piston weighs the higher rpm you can run. The less the piston weighs the less the connecting rod has to weigh. You would think rod angle is the limiting factor in rod ratio/ stroke. The 900 cubic inch pro mod engines have a rod ratio/ angle that you think would not work. (1.3 lol) They use a 11.1 inch deck height A 5.5 inch stroke. A 7.250 long connecting rod. and a 5.1 inch bore. red line is about 8000 lol rpm If you look at the rod angle you would think the piston would go through the side of the block- it does when you make a mistake.The biggest drag/ load are the valve springs. They are maybe 500 lbs on the seat- 1200 lbs on the nose x 16 x 8000 rpm. I think net lift is now 1.2 inches. NASCAR engines like to run close to the theoretical rod ratio 1.83? There is an argument over whether the lighter weight let's the engine rev faster or whether the longer rod/ higher ratio make more power. The drag racers go with lighter. NASCAR goes with rod ratios closer to ideal. If you do the load versus weight cals. you will see why light weight pistons are most important.
 

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