[GPierce]

Starting in the late 70’s we would put a brand new Diesel engine in the test cell and warm it up. When the water and oil was warm it went to full power, up to 400 hp loaded by the dyno and depending on engine model. The engine was instrumented with a blow by pressure gage in the crankcase vent which had a calibrated oriface. We monitored that pressure. You could see the crankcase pressure (blow by) drop within less than a minute as the rings seated. The whole test routine took less than 20 minutes. This brief run in was the result of cylinder sleeve machining and coatings as well as coated piston rings that didn’t need “breaking in”.

In 200O I put new cylinders on my Lycoming airplane engine. Running at 75% power I was monitoring the the cylinder head temps. After about 3 hours I saw the all 4 cylinder head temps start dropping within minutes of each other. They stabilized 20 degrees lower after about 5 minutes.
Fast forward to 2018; new cylinders again. Same routine, 75%+ power. This time the initial cylinder head temps were lower after the initial climb out, about 5 minutes. Again improved machining tolerances and coated piston rings instead of bare chrome rings on steel cylinders.
Some of these coatings are manganese phosphate. You can Google piston ring and cylinder coatings see a wide variety of processes that have virtually eliminated the need for break in.