While we are kinda on the subject of engine internals and stuff, i have a little story to tell.
When my uncle used to do autograss racing in a mk1 escort, he raced in one of the more standard classes, whereby all engine internals had to be totally standard and the cc limit is 1300cc, and when building his engine he did a little experiment that paid off.
He bought many many sets of off the shelf standard parts, such as valves, valve springs, pistons, conrods, etc, and then preceded to weigh them individually.
Now i can't remember the differences exactly between parts but out of all the bits that he had bought there was a considerable difference in weight between parts that were supposed to be a set, but once he went through lets say 5 pre packaged sets, he then had his own matched set that were near on identical (and the lightest) in weight.
He then built the engine with all these weight matched sets of parts, and the result was 6bhp more on the rollers than any previous engines that he had built, (only 1300cc engines remember) and where he would normally finish 2nd or 3rd in any given 6 lap race, with the home balanced engine he was regularly finishing 1/4 to 1/2 a lap ahead of everyone else!