The Honda 48mm (1.89") rod journal is a great idea for an engine never loaded at low RPM.
However, comparing it to a 2.375" (BBM) journal, the local oil pressure at the bearing surface is 20% lower at the same gauge pressure. The ratio of the journal circumferences determines the oil wedge viscosity, all the pump pressure does is "fill in the hole".
The difference decays as engine speed increases, and is harmless at power peak so a stronger relief spring won't help.
Needs thicker oil, larger pump, higher idle speed, and treat it like nitrous: no big power at low RPM.