Major engine-design features of the 17.6 cu in. engine are described and engine development is traced by photographs and sectional drawings.
Fuel testing with the 17.6 engine produced these results: ratings were obtained of many API-NACA pure hydrocarbons, which permitted relating variable compression-ratio results with supercharged results; Army-Navy performance numbers above 100 were established; the most sensitive fuels were indicated to be most prone to failure by preignition.
The engine also contributed greatly to the development of spark plugs. The catalytic effects of spark plug electrode materials on the ignition of methyl alcohol and unleaded benzene are discussed. Many of the more important results of spark-plug research are summarized, such as standard spark plug preignition test procedure developed using leaded benzene as the fuel; tests of many electrode materials, a range of ignition energy, hot and cold spark plugs, internal resistors, and so forth, led to a much better understanding of spark-plug gap growth; sparking-voltage requirement was related to spark-plug polarity, electrode materials, and other design and operating factors.
A post-war investigation of exhaust-valve materials in the 17.6 engine has supplied data for a more basic understanding of exhaust-valve burning.