My method is very much like Tom's...in fact the Rocket boys in SARL and I have had a number of discussions on this, as we all want to find best power without first finding the red zone...kinda one of our holy grails, if you will.
I have 10:1 pistons, and looked intently at those charts Dan posted...then read his caveat about hi compression, etc. I approach best power gingerly at race power...as Tom said. I look for the same 400 CHT max (prefer 380-390) and 200 OT (I'm usually below 195 at full power, unless its a second or subsequent hop on a warm day...heat soaking is a real game-changer in this pursuit).
I did some high(er) altitude testing in preps for the 2010 Airventure Cup, and leaned to and through peak at altitudes ranging from 9,500 to 17,500 (WOT and 2740 RPM). I was happy with my engine's performance when LOP, but the drill was to find best power at altitude, so I could get there more quickly during the race.
What I found was that for each 1,000' of altitude decrease (from 17,500 down), best power mixture (100 ROP is what I used in the tests), my engine's fuel flow increased 0.5 gph...or a 1 gph delta for each 2,000 feet of altitude change. It was fairly linear up high, but I'm not sure it is linear from sea level to 17,500'. The 13.5 gph I saw at 17,500 on test day would extrapolate to 22 gph at SL, and thus far I would not feel comfortable leaning that far at SL at max power. Perhaps best power is there, and the temps Tom and I use as our comfort limit are just not acheivable in an IO-540 at best power at SL. It may be out of detonation, and still be hotter than our limits, but how do ya know? Better safe than sorry in our books!
Interestingly, at Reno, Mark, Greg and I were using 21-23 gph in the races, and watching our temps in the same manner. The linear extrapolation from my tests would put best power at 19.5 gph at Reno's 5,000', but I would not lean that far there either. I was running 23gph at the recent PRS, and had good temps.
How this relates to 4-banger RVs would be an interesting comparison as well. Would it be a 2/3 relationship? Seems logical, and the faster of the Lancair 360's at PRS that we were with was running about 17gph at max power. Maybe Slick Cone, who ran his O-360 RV-8 at PRS has some numbers on that front.
Different ambient temps, different density altitudes, etc, will likely have an impact on those fuel flows and where best power is, so it still is an elusive target to bracket towards. And the above numbers are from one series of tests over a few days...certainly not enough to draw a final conclusion. The consequences of missing the target and getting into detonation are too severe to chance going there, so I choose to move the red knob very gingerly in SL races. Wish there was a cylinder pressure/deto-meter...another of the holy grails, eh!
On the speed versus RPM issue, in the Rocket/540 world, seems the MT 3-blade lost speed over about 2650, while our tests with the Hartzell 80" BA seem to show that that prop keeps giving back when you give it more RPM...pretty phenomenal propeller in that regard. Bob, your 76" BA may be the same kind of animal...that one test may have been an outlier...the other results you discussed (higher RPM is faster) seem more in line with our BA results. I think Slick may be trying out various RPMs with his WW200, so perhaps he can share his results as he tests and preps for Reno.
If anyone figures out the magic best power-finding method...
please let us know (well let
me know...don't tell those pesky Rocket guys!)
Cheers,
Bob