Click on my name and check out the Bearcat the P-47 and the KI-84 in my gallery pictures. I have a DA-150 in the cat and a Brison 4.8 twin in the KI. All have dummy engines in front and in fact the openings are less than half of the cylinder fin width. They all fly well in the Texas summer heat but the air that goes in is forced to pass thru the cylinders by baffles that fit closely around the cylinders.
The primary flow thru the cowling on the ground and in flight is from differential air pressure caused by the accelerated airflow over the outside of the cowling.
If the pressure in the cowl was more than a few inches Hg. difference than the outside air pressure, cowls and cowl flaps would have been blown all over the country side when the big round engines roamed the skys.
The birds that I flew with cowl flaps did not require any great amount of force to open and close the flaps and they were all manual linkages from the cockpit to the cowl flaps.
Basically if you just block off the excess area that is not directly in front of the cylinders things will work fine and you won't even have to get into mass flow rate calculations.
ORIGINAL: 3d-aholic
Simply blocking the total air flow, without directing it, so that its 3/4 less than it would be if you did nothing, is not my understanding of baffling at all and not what I read on the FAQs of the engine websites. So I would say now, I'm more confused than I was. I understand what baffling is from reading the FAQ's. However, none of them deal with a round cowl...and none of them describe a process where flat pieces are set perpendicular to the travel of the plane to "stop" air flow....all the Faqs describe a process where the flow is channelled right up to within 1/4" of the fins of the engine and air can but go one place --- though the engine fins. All of the Faqs describe a process where for the most part wood is placed parallel to the direction of the plane but directed and angled from the opening towards the engine.