Originally Posted By: jrustles
Now for the good stuff, let's focus on the bearings. The mains get fed right off the main gallery, pressure drop is minimal. What about the rods? Well, the only way they can be fed is through the crankshaft. The oil passages in the crankshaft are a pressure drop nightmare. Not only does the feed have to enter a constantly rotating orifice at the main bearing, which is already leaking volume from it's clearance, but the already pressure-dropped feed into the crankshaft via the mains must again find it's way through small, angularly drilled passages within the crank. Getting to the rod bearing orifice, we now have seen the ultimate pressure drop in an engine, compared to what we see on the gauge.
Your long and detailed post was very good, just one nuance that I'd like to add about the big end lubrication...
Because the big end is spinning, it's trying to sling its oil out from the centreline of the crank, needing pressure to force the oil "uphill" to the crank centreline, when the "centrifugal force" then slings it towards the bearing.