That`s a popular myth but it just isn`t true. When I built my Buell Lightning spec Sportster I broke it in on Amsoil that was 25,000 miles ago. Break in will take longer with synthetic but the engine will last longer.
I broke in the TDI engine in my Jetta on synthetic too....
But you need to remember the differences in machining.
The cylinder finnish on some engines is so good they are practicaly broken in before they are fired.
Clones are not so well machined.
I am still flip flopping on the correct break in for a built clone using the best finnish and parts on offer.
In short I don't have all the answeres and to be truely honest I might just used some ND 30 and 10.5 springs on the next engine jus to be sure the rings bite and the cam doesn't crap out.
As for types of oils again I am at a cross roads.
I always have put my faith in diesel rated multi fleet oils like Rotella T.
My faith has been shaken because these new versions lack many of the additives I placed my faith in.
Kart race oils DO offer some advanges if used correctly. They are generaly thinner and higher in some additives the EPA feels damage cat converters. They make more HP....
On the flip side of that they also lack many of the detergent qualities I feel are better suited to my type of engines ( unless you change the oil much more often and are willing to spend a lot more money ).
So for now I think you are best served running a quality name brand single viscosity synthetic ( depending on price ).
And thats all I have to say on the subject now.
Decide for yourself if you want to try break in lubes, race oils or something ina 20 litre pail from Walmart.
