I beam vs H beam

[DMXF]

Originally Posted by Dimis

I'm being fed all sorts of misinformation & now I'm totally confused. I need some CC forum counseling. What are the advantages of one over the other?
Ultimately, what made you go for one over the other & are H-beams worth the extra $?

Many thanks,

Some time back I did some research on this matter and found that the H beam rods are supposedly easier (cheaper) to make, so the manufacturers like to push them. While holding the rod to do the boring of the big and small end holes, the CNC equipment can easily run a cutter up the sides of the rod.

There was some laboratory test data from back some time ago that showed that H beam rod bearing oil layer thickness was a bit more uniform across the journal with the greater stiffness of the H beam in that direction, but I don't know whether the I beam they tested was the same weight or the same relative stiffnesses (you can make an I beam the same stiffness in the out of plane direction as an H beam, if so chosen). The rod manufacturers use this to justify their cheaper to make parts. The problem is the dominant loading is typically in the direction of rotation and H beams will buckle much easier in that mode, ref this example:

In the real world, the crank and block will be flexing also, which the I beam would tend to more readily accomodate, keeping the bearing from coming in contact with the journal at the edges. Anyway, I couldn't find any examples of Formula 1 engines using H beam, so the net outcome is they are not likely really beneficial. I've also heard comments that some of the better quality rods just happen to be H beam, so the quality aspect is why people are buying them, not because they are H beam.