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That's not an analysis so much as, using his own words, a "hypothetical comparison."

The fact that the OP is using a horsepower rating to gauge a rod's strength tells me that he doesn't understand enough to critique a rod design and that is pointed out in post 27. The thread falls to pieces from there. I doubt he had even figured what the engine's peak piston acceleration was.

I'm not promoting one design over another, but the possibly most powerful road racing engines to exist used tapered h-beam rods. Are they the best for all applications? Likely not.
 

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The last time I saw a guy try to race a bridge down the 1320 his reaction time was so slow the lady in the ticket booth gave him an hourglass along with his timeslip
 

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The last time I saw a guy try to race a bridge down the 1320 his reaction time was so slow the lady in the ticket booth gave him an hourglass along with his timeslip
Good point. I think it's a draw. One prob works as well as the other IMO+. It's not like most of us R running a "AA Fueler" on the street(Many folks think so) & prob track as far as that goes.
 

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Just stirring the pot a little....


:rofl:
 

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H and I are the same shape, just turned 90 degrees. You can't really say one is better than the other and will always be in every case. It's going to depend on the specific geometry of the two rods you're comparing.

It's simple enough to calculate the difference between two designs if you have the CAD geometry - just dump into ANSYS or FEA of your choice. And your comparison will be based on a specific build. High RPM vs boost vs N20 your answers will vary.
 

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This rod was used to make about 15.5hp/ci @ 11,500rpm:


and used studs:


15.5hp/ci is like a 302 making 4,700hp.

Does that mean they're the best and Top Fuel teams should use them instead of big aluminum slabs? No; it's completely application dependent....like most aspects of an engine's design.

Brilliant response, but the same principles apply. I-Beam is harder to twist.
Twisting is only one consideration in either application. I don't see too many conrods loaded directly from the side and I don't think too many bridges bear the majority of their load in longitudinal tension and compression like a connecting rods does.

I'm just saying the analogy doesn't work because the applications aren't similar.

Well the flow bench has an obvious weight advantage vs a bridge or chassis dyno
Butt dynos are lighter still, but they're even worse around a track.
 

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I would be interesting [and expensive] to have a test with two rods of the same weight, same material, one H beam, one I beam, and both ran until failure.

Then analyze how the failure's occurred.

According to another article I just read, I beam rods are generally lighter, and better suited to high rpm applications, where as H beam rods are stiffer, heavier, and better suited for high HP/TQ applications [forced induction].
 

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I would be interesting [and expensive] to have a test with two rods of the same weight, same material, one H beam, one I beam, and both ran until failure.

Then analyze how the failure's occurred.

According to another article I just read, I beam rods are generally lighter, and better suited to high rpm applications, where as H beam rods are stiffer, heavier, and better suited for high HP/TQ applications [forced induction].

Why are they "stiffer, heavier"
 

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Does that mean they're the best and Top Fuel teams should use them instead of big aluminum slabs? No; it's completely application dependent....like most aspects of an engine's design.
Well that's certainly true.

Twisting is only one consideration in either application. I don't see too many conrods loaded directly from the side and I don't think too many bridges bear the majority of their load in longitudinal tension and compression like a connecting rods does.
And an h bean is stronger across the beam. How many rods get bent that direction?

I'm just saying the analogy doesn't work because the applications aren't similar.
While the I Beam is strongest perpendicular to the Beam. The application may not be the same the the direction of the stress is.

And a good racer will wrap either one of them around the crankshaft given the opportunity.
 
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