RE: Anyone got readings OS Fx 91?
Pete,
You may also want to do a search in the '[link=http://www.rcuniverse.com/forum/forumid_114/tt.htm]Glow Engines[/link]' forum, for threads that address exactly this issue.
Unlike some other things in life; engine cooling is not all about sizes and diameters... In fact, they have but little importance.
Having a large cooling air inlet and a three times larger exit, may not necessarily cool your cowled engine.
For a cowled engine to be properly cooled, it should be elaborately baffled, to cause the incoming air to flow snugly around the cylinder and especially around the head.
The cooling air must flow relatively slowly, between the cooling fins; not just around them. And then it must be extracted from the cowl.
Even if your model has a voluminous cowl, with a large entry (even directly in front of the cylinder) and a three times larger exit hole(s); what guarantees that the cooling air will not just flow directly from the entry to the exit; bypassing the engine altogether, or that the air will at all flow in the right direction (i.e. the pressure at the exit could be higher than at the entry)???
Go to your local airport and take a look at some light, piston-engine planes, to see the elaborate baffling around the engine... It might initially appear to mask-off the cylinders altogether...
Learn and apply!