Engine compression ratio study
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The document analyzes the stress on piston and connecting rod components from increasing the compression ratio on a small block V8 engine from 9:1 to 11:1. Finite element analysis showed that at a 9:1 ratio the maximum stress was 45,810 psi, while an 11:1 ratio would cause maximum stress of 105,400 psi, below the alloy steel safety factor of 90,000 psi. The conclusion is that increasing the ratio to 11:1 would likely cause cracking and failure of the connecting rod.
Engine compression ratio study
- 1. Piston Compression Ratio Stress Analysis 08/14/17 rev B Don Blanchet 3B Associates dwb3298@verizon.net 3.4 inch dia
- 2. Study A local hot rod friend wants to know if he can safely plane the heads on hi small block V8 engine. He wants to raise the compression ratio from 9/1 to 11/1. Will the piston and connecting rod withstand the increased preesure?
- 3. Solidworks FEA Model Piston top pressure 750 psi at Crank shaft position Top Dead Center For the baseline 9/1 compression ratio Connecting rod Fixed at journal bearing 900,000 Degrees Of freedom
- 4. Results: 9/1 compression ratio max stress 45,810 psi in the connecting rod Max stress In Connecting rod
- 5. Results: 11/1 compression ratio max stress 105,400 psi in connecting rod
- 6. Conclusion Raising the compression ratio from 9/1 to 11/1 on this design will eventually cause cracking and fatigue failure at the base of the connecting rod. Alloy steel factor of safety 90,000/105,400 = 0.86 This modification is high risk.