Can Increasing Con Rod Length Lead to Detonation and Supplier Issues?

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Discussion Overview

The discussion revolves around the implications of increasing the length of connecting rods (con rods) in an engine by a few hundred microns, particularly focusing on potential effects on engine performance, piston clearance, and supplier tolerances. The scope includes technical considerations related to engine design and performance, as well as supplier issues.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Experimental/applied

Main Points Raised

  • Some participants express concern that increasing con rod length could lead to piston clearance issues, potentially causing the piston to hit the cylinder head and bend the connecting rod.
  • One participant mentions a specific guideline for piston to cylinder head clearance, suggesting that a closer distance could be problematic.
  • A participant questions the appropriateness of seeking advice on an online forum without providing detailed design information.
  • Concerns are raised about the increase in piston thrust if the con rod length tolerance is increased, with one participant humorously stating that thrust would increase by -100% if the piston hits the cylinder head.
  • Another participant emphasizes the importance of understanding detonation risks in relation to combustion chamber design when considering changes to con rod length.
  • There is a query regarding the supplier's inability to maintain tighter tolerances, indicating a potential issue with manufacturing consistency.

Areas of Agreement / Disagreement

Participants express varying levels of concern regarding the implications of increasing con rod length, with no consensus reached on the specific outcomes or solutions. Multiple competing views remain regarding the impact on engine performance and the importance of design details.

Contextual Notes

Limitations include a lack of specific design information and assumptions about the engine configuration, which may affect the discussion's conclusions. The conversation also highlights the dependence on precise measurements and tolerances in engine design.

malodeatul
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hello, what happen if cod rod length increase by few hundred microns?
 
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the closest pistojn to cylinder head clearance should be 0.050" ( 1250 microns) and having closer distance would mean the piston hits the cylinder head and bends the connecting rod. This is a V8 cast iron engine forged con rod spec and a general guide line so beware...
 
Last edited:
my supplier asking for 150 micron increase in length tolerance?
 
Well is an online forum really the place to be asking for advice? We don't know your design, we don't know what is important.

What happens if the conrod tolerance is increased by 0.15mm? The conrod could potentially be upto 0.15mm longer than previously spedified. That's really the only sensible answer we can give.
 
Thanks Chris for your concern, It all about engine performance that concern me.
My liitle concern about what it will increase the piston thrust.
 
atulmalode said:
Thanks Chris for your concern, It all about engine performance that concern me.
My liitle concern about what it will increase the piston thrust.

The thrust will increase by exactly -100%, if the piston hits the cylinder head.

As the others said, it needs MUCH more information to answer to your question.
 
What is the rod length?

What is the piston top to cylinder head clearance?
 
2milehi said:
What is the rod length?

What is the piston top to cylinder head clearance?

rod lenght-150mm
clearance-1.5mm
 
Unless you are running a true hemispherical combustion chamber, you need to think about detonation in the quench areas. But, more importantly, you need to be asking why your supplier can't hold tolerance any longer.
 

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