[skyking]

in the propeller driven aircraft, complex planes with higher speed ranges have typically used cowl flaps to regulate cooling flow and drag. some aircraft designs tried to eliminate the added workload and complexity by using the venturi effect. my early 310 was one of the latter, with fixed geometry in and out, and exhaust positioned to utilize the high energy exhaust gasses in a muffler housing.
more power=more exhaust and cooling air flow.
the variable floor NACA duct is a brilliant idea; I wonder how it worked.