In studying the history of rocket engines, you see two big technical problems. First people struggled with the issue of cooling. And next, as engines started to become larger, they struggled with the problem of combustion instability. The Germans never really figured it out, they tried to build a 25 ton thrust engine along the lines of a modern cylindrical chamber with a flat injector plate, and they were destroyed by chugging and screeching oscillation.
So the question occurs to me, why was the V-2 engine stable? I don't believe the Germans knew why, they were just lucky that the scheme of using 18 cup-shaped preburners worked. Did this configuration act like an anti-oscillation baffle?