I think there is some misconception out there on how the girdle works, and what it's engineered purpose is.

The girdles intended purpose has NOTHING to do with resisting forces in the vertical direction. As correctly mentioned the 1/4" or 5/16" thickness will easily bend from the attachment points (same goes for a big block to a lesser degree).


What it is intended to do, is to prevent the caps from moving fore/aft in the block. As the crank is pushed down against the caps, they want to "splay" forward and rearward because of the bending forces from the crank. The girdle ties the caps together in a fore/aft manner preventing this from happening. This helps prevent that bending force from being transferred up the main webs and into the bulkheads also... meaning the benefits are not limited only to the cap/block interface joint.

The splayed caps only help the block/cap interface joint by increasing clamping, but do not prevent the bending forces from getting up/through the bulkhead in the block.

If you mill the tops of the cap down, and shim accordingly, it can also slightly increase the cap strength by "strapping" across the top of the cap.

Now there is a lot to debate here because all of these blocks were built long before FEA and computer modeling to review stresses, but in my opinion the proof is in the pudding with guys visually seeing differences in their teardown inspections after adding them.