Merlins put out 2000HP on 150 octane fuel, and 2600HP on 150 octane and water injection. If I could increase my Honda's compression ratio, I could take advantage of 94 octane gas. There are absolute physical limits to what you can do with a piston engine, especially if you can't use tetraethyl lead.But then the eventual top developments of the Merlin were twice the power and the comparably sized Roll Royce Crecy tests pointed to eventually getting twice that again. Not to mention we can look to more power recovery from thermal excess and electronic engine management in addition. From 27 litres it is not unreasonable to think of having 6,000bhp to hand by now. As to what one might do with it is another matter. The Rolls Royce Crecy and Napier Nomad are, perhaps, the best OTL pointers (in different directions) to what might have been.