The efficiency is actually much worse.
The theoretically most efficient reciprocating cycle for converting heat to work is the Carnot cycle, which has a conversion efficiency of 50%. Is the 33% you’re referring to .33 * 0.50 (theoretical best) or based on joules out over fuel calories in?
I’m finally into the putting back together phase. I have a question about the cast in pedestal at the back of the lifter valley.
When I turn the oil pump with my cordless (meaning not high speed, high torque) drill, I see oil flow out from the top of that pedestal at a rate similar to how much a lifter flows.
Does anyone know what its purpose is? Unless it is the pressure relief valve, I think the oil should be going to bearings and things that need it rather than to the drain holes.
If it’s a relief valve, it seems to be relieving without a lot of work going into the oil pump.
BTW - I’m not done cleaning in there yet
“The cast in pedestal at the back of the lifter valley” you are referring to, is used by the manufacturer to drill the oil galleries after the block has been cast. They then seal the hole with a plug. There are more on the back of the block (behind the flywheel).
When building a high performance engine, some guys like to tap a thread into the hole and then put a screw in plug for secure oil pressure, that is, the screw in plug will not blow out under high oil pressure.
That plug should not be leaking any oil.
Peter 
The relief valve is in the oil pump.
Thanks for the reply. I reseated the expansion plug. I noticed it took more torque to turn the oil pump, and no oil leaking back there. I hope that lasts.That leak explains the difference I was seeing in oil pressure between idle and cruising. Per the pressure indicator idle was about 15 psi. Cruising was about 40. I will be characterizing my gauge and sender before putting it all back together so I will have a better idea what the gauge is really telling me.
If your getting the heads done with new springs, why not a new cam, lifters,timing chain, valve spring kit.
Always new valve guides. New seats, then bigger valves.
Did new guides, seats, SS valves.
As for the rest, I’m not interested in finding the weak link. I’d rather enjoy cruising and being able to take that lane on my terms.
The only racing that interests me is bracket, which requires consistency, not cubic dollars.