So after I got back from an 3/4 day breakfast, I thought it would be a good time to start playing with variables affecting the oil temp, as OAT is climbing and I was running a pretty solid 185 all way back.
After having none I now have two borrowed manometers to test the pressure differential in the cowl, and since CamTom12's is quite compact I had run the hoses and stuck it in the cockpit the other day. Pretty much ran a differential of 2.50-2.60" of water at 2350 in level flight as an average. Checked that a few times this morning.
Once back I clamped on my "nostril" idea to try and capture more air and better pressurize the upper cowl. It was a test case and therefore looks didn't matter, but I expected to get some increased pressure.
Sadly and a bit of a surprise to me, it had zero effect on pressure differential, and no affect on oil temp.
So...my conclusion is the air must not be leaving, and therefore you can't push more air into an area that is already full. So, let's go back to the "increase the vacuum" path.
I have roughly a 2" chin spoiler that I had early last year, but never truly tested to see if it was making it better or worse. So I took some duckbills and bent down 3/4" of trailing edge closer to a 90 degree angle to the flight path, and test flew it.
Oil temperature dropped roughly 5 degrees, and pressures stayed constant.
**As much as I had hoped the manometer would be a great source of reliable data, in all these tests it has really failed me. The pressure differential really didn't change with any of my modifications, but does change with rpm/speed - A change of rpm up into the 2400 range will bump the differential into the 2.75-2.85" of water range, and correspondingly going slower. (Unfortunately the oil temp doesn't drop with increased pressure at higher speed, for obvious reasons)
So the next test, to confirm the validity of the previous one and remove any doubt of the additional chin spoiler helping, was to simply remove it all together. Once again, pressure stayed constant, but oil temp climbed a full 12-15 degrees over the previous test. OAT was constant, or perhaps a degree or two cooler.
So in summation of today's tests -
~ Can't increase ram air.
~ Manometer does not see to be a good test data method, as it's just not fluctuating with any changes other than airspeed. Removing the composite prop and reinstalling the metal prop may be a telltale test on this, but some doubt has risen about maybe it not being a pressure issue.
~ Oil temp will fluctuate easily with changes, so perhaps should use that as the data point.
~ Cubcrafters wasn't aware that I had rear openings, but they (And Tom Ford) suggested rebuilding the doors to increase the rear opening size. I'd have to measure, but I anticipate the opening is 1.5"-2" at the wide point. Tom seemed to think that the Super Cub runs a 3" and greater opening on the cowl doors. I'd rather not rebuild the doors yet, but it's an option.
Knowing that the chin spoiler is making a difference encourages me to test that further. I had previously drawn up an idea of a "carbon-cub-style" center lower cowl addition, that would come off the back of the airbox that already hangs out and then fan out a bit to the back edge of the cowl. I may bend up a few pieces to test this, similar with the carbon cub, where the large center tunnel should provide a good draft behind it, right below the oil sump.
The other thing I had forgotten about, but might as well test is to throw a piece of tape on the cowl doors and stick on some leftover VG's, to see if it helps or hinders the sucking of hot air out of the cowl. There's been opinions on both sides of that idea as well.
pb