I DO think it's possible for an item to be *rebuilt* as good as, or even better than, when it was new, but it requires high quality materials on a par with the original, AND the rebuilder must know his stuff and implement it.
Absolutely, even when new they aren't anywhere near perfect. When I rebuilt mine it was virgin. The crank throw was short .002" but is easily corrected when ground. Some shops don't check this and just regrind without correcting.
Pistons in the hole .020" which doesn't help quench, poor mixture motion, and generally makes them more susceptible to detonation. Easily corrected with custom piston pin heights and/or decking the block. Speaking of which the decks are almost always uneven anyway and should be cleaned up. Even my brand new 502 crate engine sitting here is uneven.
When I tore down my DZ it also had some odd bearing wear in the main saddle. Turned out it needed an align hone, and the new bearings need to be dressed on the back side to rid them of high spots that create an uneven bearing surface once torqued down, and will generate more heat if not dressed.
Cylinder heads need a lot of attention as well. Cheap 0-ring seals on the valve stem need to be tossed, they are only marginally good at controlling oil, even with new tight guides. Best to machine for positive seals for better oil control. You really don't want oil in the combustion process, especially when pushing the compression deal with todays pump gas. Speaking of compression, mine, with all the things I mentioned, I believe the highest cylinder after all the measuring was 10.7:1, wasn't even close to the advertised 11:1.
All kinds of improvements to be made on factory stuff, lots of HP to be found as well without even deviating from the stock nature of the engine. Technically mine got a compression bump even though it's still 11:1, but now a "true" 11:1.
