I'm not going to get into the argument about test methods to determine sufficient cooling.
This is just a statement of what I have that works and works very well. See my recent article in Contact Magazine. What works for me was determined by the physical constraints of the Long-EZ firewall, and trial and error. Without looking at the archives, I don't even remember how this thread got started!

Originally I had probably the smallest installed rad volume of anyone flying a rotary. I was running the stock porting '86 NA 146HP engine to about 5400RPM cruise, less in climb, probably only developing about 120HP. I have a 1 x 3 x 9 (27 cubic inches) cabin heater core plumbed to the engine heater port that bypasses the thermostat. My main rad during the low power period had overall dimensions of 2 x 13W x 17L, with 2" being the thickness of the tanks. The actual core was more like 1.25" thick. So the core itself was 13 x 13 x 1.25 or 211 cubic inches. I donot have a coolant temp readout in degrees. I have the actual instrument panel gauges from the 1986 RX-7 installed in my airplane. In the 2nd gen RX-7 the normal coolant temperature is about 1/4 to 1/3 up from the bottom of the "normal range". Because of the thermostat it never varies from this in the car unless there is something wrong, like a coolant leak and resulting loss of coolant. With my original small rad, I did see elevated temperatures on hot days during extended climbs, the gauge would indicate about 2/3 the way up in the "normal" range. It would not run away or go above this level. I've never bothered to find out what the upper and lower limits of the RX-7 gauge are in real Fahrenheit temperatures, but that data can probably be easily obtained from the maintenance manual, other sources, or testing the stock sensor/gauge against a thermometer.

After converting to PSRU/prop December 2004, I could now rev the engine to 5400 RPM in climb and 6400 in cruise with my fixed pitch prop. Anticipating more heat with the additional power, before summer arrived I installed a new double-pass rad that doubled the core volume of the original. Two 2" tanks at the front, one 4" tank at the rear, and two 13 x 13 x 1.25 cores in between. Now, on the hottest days I can climb full power with no limit on duration, and the temperature indication never budges from the 1/3 point on the gauge. Just like in the car!

So about 450 cubic inches of radiator core will be more than sufficient to cool your 146HP rotary. Scale accordingly for more installed power?