Inertia Loading on a connecting rod

Inertia Loading on the connecting rod: a calculation of Stroke, Rod length, Rod and Piston assembly weights and RPM. Inertia is the force that will try to separate the split line, if the bolts do not have enough clamp load, or rip the pin out of the rod. The higher the RPM, the heavier the piston assembly or the worse the rod/stroke ratio, the more inertia load is generated. For example, using 4.250” stroke and decreasing it to 3.250”, the load decreases by approx. 27%. Taking the same parameters and changing the piston weight from 640g to a 540g, the load decreases by approx. 10%. If we take the Max RPM, and drop it from 9000 to 8000 the load decreases by 21%! This is why we ask for a lot of information, when designing your rod. We look at everything the rod is going to be asked to handle. As you can see, what may appear to be a small change, can have a bigger impact than you may think. Just remember that when designing a connecting rod we need 2 RPM’s: Max RPM for inertia calculations and RPM that MAX HP is made for compressive loading.


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