frogslinger is right on the money,
Rings, bearings, cylinder walls, rocker arms, springs, rollers, push rods, valves, cams all these things add to friction in the engine. While new designs of roller rockers etc reduce the friction compared to old rockers, they still add an element of friction. When an engine is newly built to factory or B&B standards it is at its highest operating friction due to the close tolerances in these parts. The hardest start for an engine is its very first, as the rotating parts are tightest in their bearings, and the piston rings are as sharp as they will ever be (they will wear a section of the cylinder wall very slightly), and valve springs strongest of their life cycle.
Long as you follow the break in procedure you should see a noticeable improvement around 1500miles. Break in is very important as it will give you a more reliable and efficient engine. The best part of a new running engine is the oil system, filter and passages are clean, oil is at peak viscosity, and the pump flows its highest numbers. Its been about 10 years since I've been in the autoparts/engine business, but the rule then was not to use synthetic oils in any vehicle parts until 8K miles. you want the normal engine wear to get the engine to the designed operating tolerances. Do your first oil change at 500 miles and have them open up the oil filter and check for filings. A small amount (rub your finger on the paper/silicon part) of grit will be normal, large filings are abnormal cause for concern.
Ok I'm going a little long in the tooth here sorry. After 8k miles you should be safe to change to synthetic oil, trans fluid, and diff fluid that is of the same or similar weight.
I figure 90% of us on here know this stuff and have similar experiences, I'm sure some will tell of the 20 minute break in. Personally I dont like it for road vehicles that need to last, its fine for a race engine that will be rebuilt every 1500 miles but chances are its all forged parts.
Anyone hear of cryo dipping blocks anymore? I know it was a fad around 2000 for strengthening blocks.
Never use snake oils like pro-long etc. My Goat engine lasted about 100 miles after using it. When i tore the engine down the oil looked fine, but the next morning in the pan on the cold floor it had a hard waxy layer on top. the good side of it was "Hey the engine is out...lets add some parts!". I miss the simple climb under the hood with a foot on each side days of yore!
