I alwayays heard that I-Beams take more power but H-beam can take more RPM.

look at this site.

http://www.grapeaperacing.com/GrapeApeRacing/tech/connectingrods.pdf

They say that a H-beam are better for low end grunt?

The theory is correct; a bar in tension will yield when the stress (Force/Cross-Section Area) exceeds the yield stress. Nothing too scientific there. A bar under compression will buckle when it becomes unstable; increasing the second moment of inertia means it can withstand a larger compressive load before it buckles. Putting more metal farther away from the bending axis will increase the moment of inertia, which is apparently the function of the H-beam's two thin plate-like sides of the rod beam.
My question is: aside from going into a hydro-lock scenario, how many rods have you seen buckle? I'm no pro engine builder, but unless a valve is smacking the top of the piston, I can't see any well designed rod failing in compression, I-beam or not....

The main loading by far is in tension. Stopping the piston at TDC at overlap. I've never seen a rod fail in compression. I suppose it could happen.

Originally posted by 70L34:
The theory is correct; a bar in tension will yield when the stress (Force/Cross-Section Area) exceeds the yield stress. Nothing too scientific there. A bar under compression will buckle when it becomes unstable; increasing the second moment of inertia means it can withstand a larger compressive load before it buckles. Putting more metal farther away from the bending axis will increase the moment of inertia, which is apparently the function of the H-beam's two thin plate-like sides of the rod beam.
My question is: aside from going into a hydro-lock scenario, how many rods have you seen buckle? I'm no pro engine builder, but unless a valve is smacking the top of the piston, I can't see any well designed rod failing in compression, I-beam or not.... So what you are saying is that a I-Beam are better for High RPM and the Low Truck engine should use H-beam carrillos? ;)