Do a serch on engine cowling
Edit: or better still, engine baffling

NACA engineers spent a lot of effort to get reliable engine operation and cooling, without reducing airplane performance. There is a wealth of information there.

The inportance of this issue, still hot after 80 years, can be gathered from the [link=http://history.nasa.gov/SP-4219/Chapter1.html]naca files history [/link] from which I quote:
"
As most successful research programs do, the NACA cowling investigation started with a question: "Is it possible to extend a cowling outward over the exposed cylinders of a radial-air-cooled engine without interfering too much with the cooling?" It is significant for NACA history that the question, which brought the breakthrough counterintuitive answer, was asked at the NACA's first annual manufacturers' conference, which was held at Langley Memorial Aeronautical Laboratory on May 24, 1926. This event became the NACA's "rite of spring." A combined technical meeting and public relations extravaganza, the annual conference gave the NACA research staff an opportunity to ascertain the problems deemed most vital by the aircraft industry so that it could incorporate them as far as possible into its research programs. At the same time, the conference gave the staff a chance to publicize its recent accomplishments before individuals who rarely had the time to read the NACA's published technical reports but who needed, and wanted, to know what the NACA was doing. The conference also gave the research staff at Langley a chance to bang a big drum before congressmen and other public officials who "had neither the time nor the qualifications to read the technical reports" but who played critical roles in the appropriations of government money. The event started in 1926 as a modest and relaxed one-day affair, but it soon grew into an elaborately staged pageant that took weeks of preparation by the NACA staffs both at Langley and in Washington. By 1936, the spectacle lasted two days, the first day for executives of the aircraft industries and government officials, the second "for personnel of the government agencies using aircraft, representatives of engineering societies, and members of professional schools." In 1926, only forty-six attended the conference; ten years later, more than 300 people were attending each session, including aviation writers who reported fully on the laboratory's presentations in newspapers and journals.9
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