A year had passed between the making of engine 100 and 120, yet the reliability had not improved. Although unreliability was the immediate cause of failure, there were two design defects which would have doomed the engine even if it had been reliable. All the Packard diesels were of the 4-stroke cycle unblown type, yet the most successful airplane diesels were of the 2-stroke cycle blown type.[30] The advantages of the latter type for aeronautical use are that it is of a more compact engine, of lower weight and greater efficiency.[31] The engine was therefore built around the wrong cycle. The Packard diesel of 1928 was designed to compete with the Wright J-5 "Whirlwind" which powered Lindbergh's "Spirit of St. Louis" in 1927.[32] The specifications were within two percent of each other. The diesel engine's fuel consumption was far less although its price was considerably higher. _Packard Diesel_ _Wright J-5_ _DR-980_ _"Whirlwind"_ Diameter (in.) 45-11/16 45 Horsepower 225 225 Weight (lb) 510 510 Weight-horsepower ratio 2.26 2.26 Fuel consumption (lb per hp/hr at 0.40 0.60 cruising). Cost $4025 $3000 The advantages of lower fuel cost and greater cruising range offered by the diesel engine would be relatively unimportant to a private pilot flying for pleasure, but would be vital to the commercial operator using airplanes powered by engines having several times the horsepower of the Packard diesel. Its size, moreover, was too small for the technology of fuel injectors.[33] The Packard Company realized that the production engine was too small.[34] In 1930 a 400-hp version was built but was not put into production, probably because of the unreliability of the 225-hp model. The fourth principal reason why the engine failed is explained by the following quotation from _The Propulsion of Aircraft_, by M. J. B. Davy (published in 1936 by His Majesty's Stationery Office, London):