Interesting replies here, in terms of what some see and not "worth it" versus what others results have been. I think a caveat to the question should be what is the intended purpose of the engine and race program. I certainly will approach a 10 second bracket build differently that a heads up car. I think this is a VERY valid argument to be made. Yes we still approach the 10 second bracket build with the same professionalism but there are things you simply DO NOT need to do to build something that will live in that world that you absolutely MUST DO in a heads up deal. Intended purpose and goals is what matter. Having said that round is round, flat is flat and that will never change. Quality machine work is always important no matter the level. And often times is the difference between that 500" Indy motor that runs mid 10's vs the one that runs mid 9's with basically the same components. There is power in things as simple as a valve job. Properly matched components in another issue that I see a lot of. Lastly I don't think most people who are looking to get everything out of a combo are willing to pout in the time and testing it takes to separate themselves from the rest.

As for what I've seen work in terms of performance or longevity, most have been mentioned. Center counter weight cranks, proper lifter location and angle, bigger cam cores, hipped blocks/heads, smaller ring pack, lighter/stronger pistons, valvetrain CONTROL, cylinder head development(this NEVER ends), intake evolution(also NEVER ends), more compression ESPECIALLY in aluminum blocks(numbers that most we be scared of), oil control, oil pressure, oil viscosities, carburetion(see heads and intake) are just a few of the things I have seen that make a difference. Not even to get into torque converters, low friction transmission and ratios, low friction third members and =gear treatments and fluids, low friction bearings in the drivetrain, chassis tuning etc etc