GRIMES, C., "AIR-COOLED AUTOMOTIVE ENGINES," SAE Technical Paper 230037, 1923, doi:10.4271/230037.
The author believes that the universal power unit will be direct air-cooled, but states that the direct air-cooled engine is now in the minority because, until very recently, there has not been a sufficiently broad series of established engineering facts and development work available to form a foundation for improvement. The satisfactory air-cooling of an 8 x 10-in. cylinder has been reported, and the development in a smaller cylinder of 138 lb. per sq. in. brake mean effective pressure; also, in a three-cylinder, air-cooled, radial-engine, a brake mean effective pressure of more than 125 lb. per sq. in. was developed and the engine endured beyond the ordinary expectations for water-cooled engines. Since these sizes and values are larger and greater than those of standard automobile engines, even though these developments may have been accomplished through the use of high-grade airplane-fuel, delicate aluminum finning and costly cylinder construction, the author feels justified in the conviction that direct air-cooling already is a success. The paper is devoted to a detailed and illustrated description and discussion of the engineering features of the car built by the company represented by the author.The direct air-cooled engine already has been developed to a state of perfection that should, in a very short time, allow it to prove the superiority of direct air-cooling. When constructed properly from recent designs it will be found that its exhaust-valves will be cooler, the carbon formation less and that it will be free from burnt and warped valves that so often are caused by the formation of a lime deposit in the water-jacket adjacent to the cylinder-head and the valve-seats. The universal power unit will be direct air-cooled because it already has been proved superior in the desert and for polar-expedition usage.At present, the direct air-cooled engine is in the minority because, until very recently, a sufficiently broad series of established engineering facts and development work was not available to form a foundation from which the air-cooled engine successes of the immediate future could spring. S. D. Heron reports the satisfactory cooling of an 8 x 10-in. cylinder and the development in a smaller cylinder of 138 lb. per sq. in. brake mean effective pressure, which is decidedly more than that developed by any standard automobile engine. C. L. Lawrance's three-cylinder radial-engine endured far beyond the expectation for any water-cooled engine and showed a brake mean effective pressure of more than 125 lb. per sq. in. which, once again, is far higher than that used by any standard automobile engine. Although the above developments may have been accomplished through the use of airplane fuel, a delicate aluminum finning and costly cylinder construction, I feel confident that the results should warrant the conviction of the most skeptical that direct air-cooling is a success and must be recognized as such if further successful engine development is accomplished.