Jonathan_S wrote:snip
And from what I've heard tuning those giant F-5 engines to run smoothly and not generate hot spots that would eat the rocket bell was more art than science. None of them worked perfected straight off the line, they all needed individualized adjustments. But the people skilled and practiced in that art are long retired (or dead) and aren't in practice. So you might as well design a modern descendant of the engine since you've got to relearn all the tuning tricks anyway, so no reason to stick to 50 year old plans and materials since they don't give you "proven off the shelf capabilities" anyway.
Minor nit. The first stages engines for the Saturn V rocket were F-1 engines built by Rocketdyne division of North American Aviation. The tuning process was actually the test firing each engine subjected to (at Huntville, since that was the only place that had a test stand large enough to handle a 1.5 million lb thrust. The second and third stages of the Saturn V were powered by J-2 engines, which were unique in the day, as they were in fact restartable, even though that feature was not used for the 5 second stage engines, it was for the third stage engine as that was how trans-lunar injection was done.