Originally Posted by
DHfan
Bill Gunston's World Encyclopedia of Aero Engines confirms everybody except the OP's views.
There was absolutely no connection between the Rolls-Royce Ghost engine and the Eagle. As stated the Ghost was a side-valve cast-iron monobloc and the Eagle had overhead cams and individual steel forged cylinders with welded water jackets.
Far from R-R not knowing about about the Grand Prix Mercedes, Lieutenant W.O. Bentley (RNAS) of the Admiralty suggested that the Mercedes cylinders would be a good starting point, as R-R only had experience with cast-iron monoblocs.
On the first Sunday of the war the car was towed to Derby by Bentley and his boss where the engine was dismantled by Ernest Hives, later Lord Hives and R-R's chief.
Royce spent nearly a month evaluating alternative engine layouts, taking particular care not to infringe any Mercedes patents. He finally settled on a water-cooled V-12. Bentley suggested the use of aluminium pistons, as opposed to cast-iron.
The Eagle did have epicyclic reduction gear, as did the Condor which followed it. It was only when Rowledge from Napier arrived that R-R switched to spur reduction gears on later versions of the Condor.
Thank you for that detail I will add it to my collection.