If I may point out a few thigns that are not being considered here. . First off. . Fryfly, you are DEAD wrong, and you need to learn a few thigns about metallurgy, oil properties, wear-in of closely fitting parts, and what exactly goes on inside an engine before you start lambasting engineers and people who study these things for a living. I've read dozens of your posts on other subjects. You are nothign but an uninformed instigator and problem child. . please remove yourself from this discussion.

Now. . concerning wear-in of parts in the reciprocating assembly of an engine, specifically the piston, rings and cylinder bore. . . It IS necessary to have some "shearing off" of high spots to achieve optimum ring-cylinder seal. what EVERYONE forgets is that the "seal" is nto accomplished by direct metal-metal contact, but by the OIL that is mixed in with the gasoline. . This is true for every piston engine out there. The best seal is achieved with "almost" perfectly polished parts, but NOT perfectly polished parts. . WHY?? Because, if you have perfectly smooth surfaces, there is no place to hold the oil that is necessary to make the hydrodynamic seal between the ring and cylinder, the oil gets wiped off the surfaces, and blow-by occurs. Even hard-chromed cylinders, with extremely smooth plated surfaces, have microcracks in them in order to retain oil for lubrication and sealing purposes.

How best to achieve this "matching" of piston, ring and cylinder wall? Well, first off. . you do NOT want to wear on the piston. . it's soft aluminum and any adverse wear on it can gall it and make it drag as the high spots rub against the cylinder wall. So, you want the piston skirts to remain as smooth as possible so that their large area "floats" on the polished bore. this requires high amounts of lubrication while the cylinder and ring are wearing in to eachother. Notice I said AMOUNTS, not meaning lubricity but actual physical mass. You need this oil so that the piston can float on it as it glides up and down the bore. What you do NOT want, though, is to over-lubricate the ring-cylinder interface, which means you need a large amount of oil for the piston to float on, but it shoudl ahve a low shear-strength so that the ring can displace enough of it to wear against the cylinder properly as they polish eachother. that being said, using a high sheer strength synthetic oil is a BAD idea during break-in, since it's high film strength will actually prevent the ring-cylinder wear necessary to polish them. The use of synthetic oil has, therefore, an adverse affect on what you are trying to do while breaking an engine in, while using a petroleum based oil (with lessor film and shear strength) in higher concentrations will achieve exactly what you are trying to do.

Now, after the break-in period, usually 10-15 gallons or about 4-5 hours of run time, we no longer want to 'wear-in" the ring-cylinder interface, since 90% of that process has already taken place. What we want NOW, is to utilize the finely matched piston/ring/cylinder we have just achieved, to its greatest potential, and this is where synthetic oils excel. You can use them in lower concentrations, allowing more gas than before (and adding to the power slightly), they withstand impact and shear forces better than the petroleum oils, so they will protect the engine better under rigorous use, and with their thinner consistency they will have less overall drag on the internal components than thicker petroleum oils, thus slightly increasing power. Also, since synthetic oils do not "burn" as much in the combustion chambers, but remain in a lizuid state for the most part, they will carry away more heat in the exhaust gasses as they exit the engine, helping to keep the engine cooler than petroleum based oils.

The SAE is right. . I don't care what blow-hard bench-engineers at the flying field may say otherwise. Teh "professionals" at the SAE have looked at things and studied these problems for generations .. I'd trust their judgement long before a fellow modeller who tries to contradict them.