Have 4-probe CHT
I have the temperatures for many tests and configurations but not back before the ramp plugs were installed. Today I made a test flight checking for performance difference between minimum and maximum spark plug gaps for my O-360-A1A and found the speeds were within one tenth of a knot of identical using the NTPS spread sheet method (the USAR handicap procedure indicated a nonexistent 2 knot difference). With the 0.016" gap the the CHTs were lower than with the 0.021" gap as shown below:
1-318 328
2-354 377
3-362 371
4-321 342
I talked to a Lycoming customer service rep and confirmed that they want the engine operated in the 300 - 400 F CHT range. That is where I attempt to keep it. I have incrementally reduced the size of the cooling air inlets with test plugs using the CHT as the control limit parameter. I found it very easy to increase the the CHTs in a directly related manner but I was completely unsuccessful in increasing the aircraft TAS at the same time. Previously I had used the U. S. Air Race Inc. Handicap procedure to measure TAS. I have gone back and calculated the TAS using the NTPS (Naval Test Pilot School - I think that's what the letters mean but the important thing is it eliminates the wind impact by direct calculation not three direction averaging) spread sheet - Xcell. Based on this new information there may be a slight increase in speed associated with a 3/4" plug at the inboard edge of the stock inlet. From there the speed decays with each additional 1/4" of plug thickness. There may be a small speed increase in there somewhere with the stock cowl but it is very elusive and may in fact not exist. I have 27 personally recorded test flights with many associated data points (date, temperature at 6000 ft pressure altitude, altitude actually flown to maintain 6,000 ft density altitude, oil temp, oil pressure, manifold pressure, RPM, all four EGTs and CHTs the USAR TAS and NTPS TAS. I believe the plugged ramps of this thread and the lower cowl baffling at the rear of the engine combined with the horizontal baffles crossing the valve covers have given me some increase in speed but I am very skeptical about any further gains without significant cowl changes, more power and a better prop.
Bob Axsom