Ok, I've had some time to fly with the modified cowl exit ramp and I am happy to report a pretty substantial decrease in CHT's, and modest increase in TAS/IAS.
Lycoming IO-360-A1B6 stock except for Dual Lightspeed PIIIs @ 20°
Hartzell 7497-2 (72")
Flight Test Parameters:
6500Ft MSL, 30.05InHg
CHT °F 1: 312, 2: 340, 3: 312, 4: 294
Oil Temp: 190°F
CHT °F 1: 297, 2: 322, 3: 311, 4: 278
Oil Temp: 186°F
Your mileage may vary, but I'm liking the results and temperature margin that this widget provides.
Remove and replace horizontal exhaust stack brace with NACA 0024 shape -or- similar.
It's been suggested that using Vettermen's alternative firewall mount for exhaust stacks is the way to go, but I respectfully disagree; there's just too much lyco-shake going on and I fear the ball joints don't have enough range or ease of motion to absorb it.