The Dewar Trophy was a cup donated in the early years of the twentieth century by Sir Thomas R. Dewar, M.P. a member of parliament of the United Kingdom (UK), to be awarded each year by the Royal Automobile Club (R. A .C.) of England "to the motor car which should successfully complete the most meritorious performance or test furthering the interests and advancement of the [automobile] industry".
Some of the trophy winners include:
- 1906 - Stanley twins for their land speed record in the Stanley Steamer 
- 1907 - Rolls-Royce Limited, for 40.50 hp model covering 15,000 Miles
- 1908 - Cadillac, for parts interchangeability. The award was actually presented in 1909.
- 1909 - Daimler, for their Knight sleeve-valve engine.
- 1912 - Cadillac for the electric starter and electric lights.
- 1922 - Armstrong-Siddeley Motors Limited, for 10,000 Miles trial
- 1925 - Rover Company Limited, for 13,96 hp car, Fifty ascents and descents of Bwlch-y-Groes
- 1929 - Violet Cordery, sister-in-law of Noel Macklin, for driving an Invicta for 30,000 Miles at Brooklands
- 1951 - Jaguar Cars Limited, for performance in four major international events
- 1959 - BMC and Alec Issigonis, for design and production of Mini
- 1963 - Coventry Climax Engines Ltd, for Grand Prix racing engines. Presented in 1964.
- 2014 - Mercedes-AMG High Performance Powertrains, awarded for the PU106A Hybrid Formula One power unit.
1908 Trophy-winning performance
On Saturday, 29 February 1908, three Model Ks from the 1907 Cadillac production were released from the stock of the Anglo-American Motor-car Company, the UK agent for Cadillac automobiles, at the Heddon Street showroom in London (these were engines Nos. 23391, 24111 and 24118). The three cars, all registered in London under the numbers A2EO, A3EO and A4EO, were driven 25 miles to the Brooklands race track at Weybridge. There, the cars completed ten laps of the track, or approximately 30 miles, before being locked away until Monday, 2 March 1908, when they were released and disassembled completely, using only wrenches, screwdrivers, hammers, and pliers. Each car was reduced to a pile of 721 component parts, which were then scrambled into one heap by the RAC. Eighty-nine parts requiring extreme accuracy were withdrawn from the heap, locked away at the Brooklands club house and replaced with new parts from Anglo-American's showroom stock. The parts were then sorted into three piles, each with all the parts needed to assemble a car. A mechanic - Mr. E. O. Young - reassembled the cars with the help of his assistant - Mr. M. M. Gardner. Sometimes they had to work ankle-deep in water, using only wrenches and screwdrivers. The third car was re-assembled by Thursday morning, 12 March. With the painted parts on the original cars not being identical in color or style, the reassembled cars were mismatched in appearance, gaining the nickname "harlequin cars". By 2 p.m. on Friday 13 March the three cars had completed the mandatory 500-mile run with singular regularity. Only one point was lost owing to a broken cotter pin in the ignition lever (promptly replaced from stock). During the event, it was reported that one of the sheds where the parts were stored became partly flooded during a heavy storm and some parts became rusted. Only oily rags could be used to remove all traces of the immersion. On completion of the test, one of the cars was locked away until the start of the 2000-miles reliability trials in June 1908. It came out the winner of the R.A.C. Trophy for its class. Parts interchangeability had been publicly demonstrated and field tested.
1909 Trophy-winning performance
Immediately following the introduction of the sleeve-valve principle into the Daimler engine, the Daimler Company in 1909 asked the Royal Automobile Club to frame conditions of a test that should be of unprecedented severity and would demonstrate in the most public manner possible that the new Daimler engine was in every way reliable.
The two engines selected for this test were a 38 and a 22-h.p., having a bore and stroke, respectively, of 124 by 130 mm. and 96 by 130 mm. They were bolted down to the test bench close together in one of the large engine testing shops at the Daimler Works. The section of the shop in which they were placed was railed off and under the sole charge and observation of the R.A.C. officials from the start of the test to the finish. The observers kept watch day and night just as on board a ship, and periodically tested the revolution counters and spring balances to ensure that the engines were always running under full load. Every possible precaution was taken to keep constant and close observation upon the test, and there were never less than two observers on duty.
Both engines were started up at 6 a.m. on Monday, March 22, 1909, and each completed the 132 hours' bench test on the following Saturday evening. To appreciate more clearly the severity of the test, if the larger engine had been driving a car during the whole time, with the standard Daimler gear ratios, a distance of no less than 8,252 miles (13280 km) would have been covered, at a mean speed of 43.45 m.p.h. (69.92 km/h) while the smaller engine would have covered, similarly, a distance of 8,830 miles (14210 km) at 48.4 m.p.h. (77.9 km/h). The disparity in speed and distance between these results is, of course, attributable to the higher rate of revolutions of the smaller engine.
-- Details of the 38-H.P. Engine Test --
First Bench Test-
The speed of the engine was 1200 r.p.m. giving a limit of 50.0 h.p. below which the h.p. was at no time to fall.
The duration of the test was 5 days 14 hours 15 minutes or 134.25 hours.
There were no stops incurring any penalties.
There were five stops totalling 1 hour and 56 minutes which did not incur any penalty under Rule 6 (2)
The load was eased for a total of 19 minutes for brake adjustments, but the engine was not stopped. Average horse-power recorded, 54.3.
Petrol consumed, 614 gallons equal to .679 pints per horse-power hour.
On completion of the first test, the engine was removed from the bench and fitted under observation to the chassis without any vital parts being disturbed. A standard type four-seater body was fitted and the car proceeded from Coventry to Weybridge - 112 miles (180.2 km). The average weight of the car and passengers on the road was 4,085 lbs = 1 ton 16 cwt 1 qr 25 lbs (1852.9 kg).
The runs on Brooklands track amounted to 1,930.5 miles (3106.8 km)at an average speed of 42.4 mph (68.2 km/h) with an average weight of car and passengers of 3,805 lb (1726 kg). A distance of 5 miles was traversed in running to and from the car-headquarters and the track, and this with the return journey to Coventry made a total mileage of 2,159.5 (3474.5 km).
The petrol consumption on the track was equal to 20.57 m.p.g. and on the road 19.48 m.p.g. The ton-miles per gallon of fuel were 34.94 on the track and 35.97 on the road.
Final Bench Test
On arrival in Coventry, the engine was replaced on the test bench and run for 5 hours 15 minutes during which there were no stoppages of any description; the load was eased for 15 minutes for brake adjustments.
Average horse-power recorded, 57.25.
Petrol consumed, 22.5 gallons = .599 pints per horse-power hour.
The judges append the following remarks to their certificate: "The engine was completely dismantled, and no perceptible wear was noticeablke on any of the fitted surfaces. The cylinders and pistons were found to be notably clean. The only perceptible wear in any part was caused by two joint pins rubbing against adjacent parts. The ports of the valves showed no burning or wear."
-- Details of the 22-H.P. Engine Test --
First Bench Test-
The speed of the engine was 1,400 r.p.m. giving a limit of 35.3 h.p. below which the h.p. was at no time to fall.
The duration of the test was 5 days 12 hours 58 minutes or 132 hours 58 minutes. There were no stops incurring any penalty.
There were two stops of 17 minutes total duration, which did not incur any penalty under Rule 6 (2) The load was eased for a total of 41 minutes for brake adjustments, but the engine was not stopped. Average horse-power recorded was 38.83.
Petrol consumed, 476.5 gallons equal to .739 pints per h.p. hour.
The conditions for the running test were the same as for the 38-h.p. car test, but with varying figures as to the results.
Average weight of the car and passengers on the road was 3,512.5 lbs (1638.6 kg); on the track, 3,332.5 lb (1511.6 kg).
Distance covered on Brooklands track, 1,914.1 miles (3080.4 km).
Average speed, 41.88 mph (67.4 km/h).
The petrol consumption on the track was equal to 22.44 m.p.g. and on the road 19.48 m.p.g. The ton-miles per gallon of fuel were 33.37 on the track and 31.19 on the road.
The total mileage of 2,143.1 (3449 km).
Final Bench Test
Duration, 5 hours 2 minutes. No stoppages of any description; the load was eased for 1 minute. Average horse-power recorded, 38.96. Petrol consumed, 18.25 gallons = .749 pints per h.p. hour. The judges append the following remarks to their certificate: "The engine was completely dismantled, and no perceptible wear was noticeablke on any of the fitted surfaces. The cylinders and pistons were found to be notably clean. The ports of the valves showed no burning or wear."
- Invicta - Double Dewar Trophy winner: 1926, 1929.
- Fred Marriott – driver of the Stanley Rocket, the car that has held the Land Speed Record for a steam-powered vehicle from 1906 to 2009.
- Ricardo plc - Double Dewar Trophy winner: 2002, 2005.
- Goodman 2004, p. 33.
- See list of winners under "Past Winners" at the Dewar Trophy page on the Royal Automobile Club website
- Historians may have personalized this award which, as stated, was given to a "motor car," and not to a person or corporation
- Daimler Catalogue and Price List, The Daimler Co. Ltd., 1927, p. 76
- Jones 2002.
- Holland 1908b, p. 7.
- Holland 1908a, p. 2.
- Rubenstein 2001, p. 203.
- Holland 1908c, p. 11.
- Holland 1908d, p. 9.
- St. John C. Nixon (1946), Daimler 1896 to 1946: 50 Years of the Daimler Company, G.T. Foulis & Co., pp. 120–122
- "UK team breaks steam car record". BBC News. 25 August 2009. Retrieved 26 March 2015.
- Goodman, Bryan (2004), American Cars in Prewar England: A Pictorial Survey, Jefferson, NC US: McFarland, p. 33, ISBN 0-7864-1540-1, LCCN 2003019129
- Holland, J. P. (5 March 1908a). "Motors and Motoring: The Cadillac Trial". The Manchester Courier (16014). p. 2. Retrieved 26 March 2015 – via British Newspaper Archive. (subscription required (. ))
- Holland, J. P. (13 March 1908b). "Argument for Cheaper Cars". The Manchester Courier Weekly Supplement. LXXXIV (16021). p. 7. Retrieved 21 October 2014 – via British Newspaper Archive. (subscription required (. ))
- Holland, J. P. (19 March 1908c). "Motors and Motoring: The Cadillac Trial". The Manchester Courier (16026). p. 11. Retrieved 26 March 2015 – via British Newspaper Archive. (subscription required (. ))
- Holland, J. P. (11 November 1908d). "Motors at Olympia". The Manchester Courier Weekly Supplement (16229). p. 9. Retrieved 26 March 2015 – via British Newspaper Archive. (subscription required (. ))
- Jones, Mike (February 2002), "History of the Cadillac Motor Car", modifiedcadillac.org, archived from the original on 17 December 2013, retrieved 21 October 2014
- Rubenstein, James M. (2001). "7 From a Class-based market...". Making and Selling Cars: Innovation and Change in the U.S. Automotive Industry. Baltimore, MD US: The Johns hopkins University Press. ISBN 0801867142. LCCN 00012496. Retrieved 26 March 2015.
- "The Dewar Trophy". Royal Automobile Club. Past winners. Archived from the original on 28 October 2013.