Stove, seems you've "stoved" you're Stovebolt.
I'd guess the rod broke at the wrist pin and swung around busting the side of the block.
Or the rod bolts broke, cap came off and crank left the rod and most of a revolution later smacked into the side of the rod pushing it out the side of the block. This might be more likely?
Excessively high RPM probably the cause, what was it running? Or what gear ratio, tire size, and MPH to then calculate the RPM?
