The Rolls-Royce 20 hp was one of four car models to be produced as a result of an agreement of 23 December 1904 between Charles Rolls and Henry Royce.[2] Badged as a Rolls-Royce,[3] the 20 hp was produced during 1905 and 1906 by Royce's company, Royce Ltd. at its factory in Cooke Street, Hulme, Manchester. It was sold exclusively by Rolls' motor dealership, C.S.Rolls & Co., at a price of GBP650.[4] The 20 hp was exhibited at the Paris Salon in December 1904, along with the 10 hp, 15 hp and engine for the 30 hp models.
The engine was made of two separately cast two-cylinder units which were common with the two-cylinder 10 hp and six-cylinder 30 hp types sharing their bore of 4 in and stroke of 5 in. It is water-cooled and of 4118 cc capacity with overhead inlet and side exhaust valves Early cars had a high-tension ignition system using pre-charged accumulators, a