I’d be interested to hear answers to this… At Duxford in September the biggest difference in sound came from two largely similar aircraft – the Griffon powered MkXIVc and MkXIX which I understand are based on the substantially the same airframe, although I’m not sure off the top of my head what mark of Griffon each was using. The XIV had an almost Merlin-y sound, while the XIX had the much more traditional ‘growl’ associated with the Griffon.

I have heard that the firing order influences the tone of an engine a lot, hence the Merlin and Griffon having substantially similar geometry but completely different sounds.