i have rebuilt late model imports w/ oil clearances going into the Ten-thousandths place and old school domestic SB1's with oil clearances going into the thousanths. also custom fabrication and modification on the engines to alleviate some inherent design flaws from the factory. its fun, it does teach you respect for you rmotors, but it also means that you know EVERY single nut and bolt has been gone through, torqued and retorqued and all the clearances are spot-on and that it wasnt thrown together. when people build motors for other people, there is less urge to get it right since they will not be the ones driving it when it craps out. however, i have no desired to rebuild a rebult engine, so i do everything right the frst time, and go above and beyond factory specs/equipment.