Sorry, Oliver. Didn't mean to do that.
I'm assuming everyone knows what the Lycoming Technical Installation Manuals are, and has them in hand for the particular engines they work with (BTW, if you call Lycoming, the folks who answer the phone probably aren't going to be familiar with them, and may tell you there is no such thing). There is. Talk to the Tech guys. What you are after contains the required mass flow curves and the massflow vs pressure drop relationship for your engine model. You use this information to size your inlets and outlet for climb and cruise. The inlet velocity ratio should be between 0.3 and 0.8 to maximise dynamic ram recovery efficiency. I usually design for 0.4 as a compromise.
When doing engine cooling calculations, Lycoming makes the simplistic but conservative assumption that the face rise (the temperature difference between the upper and lower plenums) is a constant 150°F. Pratt and Whitney calculates that difference based upon the horsepower being produced by the engine. When calculating engine cooling, I use the Pratt and Whitney equation for face rise instead of the Lycoming assumption (it usually allows smaller inlets snd outlet to be used). I do use the Lycoming methodology for calculating upper and lower plenum temperatures, pressures, densities, and mass air flow for cruise and for climb. This is how you size the inlets and outlet. The system is almost always in outlet control.
Re cooling drag, it can be expressed as pounds of drag, or as the horsepower required to move the cooling air through the cowl. Six of one, half a dozen of the other.....