Some anorak info: During my short employment at Rolls Royce (don't ask) the Dart was under development, having flown a few year's earlier. The factory joke was that the Dart had been intended to produce 1000hp and weigh 800lb. but ended up weighing 1000lb and producing 800hp. Development when I was there (spectator only) was concentrated on improving the compression ratio by re-design of the compressors and reduction in clearances between the disk and the case. In the end compressors were milled from solid on a hugely expensive machine, leaving the front faces closed.
Dick