Let's look at the propeller as a wing, and recognize that the wing makes lift (thrust) by a combination of angle of attack (pitch) and airspeed (RPM). f the two, the airspeed is more influential, since the lift equation used the velocity squared. At 5500 rpm the prop blade tip is moving at 740 feet per second (with a 2.43 reduction box), at 5800 rpm it is at 780 ft/sec. The difference i thrust is about 11%, assuming the engine was producing the same power. But with the engine producing 4 HP more power at 5800, that would make the prop thrust about 15% higher at 5800.
Just to report to the group, my 582 Blue Head had 119 psi on each cylinder with 160 hours, and the next year had exactly the same reading (119 psi) with about 80 hours more time. These numbers were recorded with an electric starter.
The HACMAN leans the fuel mixture using the same method as the Rotax approved HAC system (which is illustrated in the Rotax parts manual in the accessories section), except the manual mixture valve. It basically tricks the carb bowl pressure to a lower pressure, making the carb deliver less gasoline to the metering valve (functionally the same as having a smaller main jet). I used a HACMAN on my 582 for 3 years, and it always produced clean plugs and high egts, as I flew from 11000 foot legs in Wyoming to sea level long cruises. I do think the simple mixing valve and tubing set is not worth $200 and I applaud the guys here who make it cheaper and simpler!
Progress check: The engine install is complete, with HACMAN installed and cowling cut (and reinforced). Landing gear complete, wings both now spread and bolted, tail reinstalled. Battery and ELT reinstalled. To Go: Brake lines install, fill and bleed brake system. Electric fuel pump, Warp Drive Prop. Final overall inspection, Ground runs, Fly! I am frustrated that I have a planned trip that starts Saturday for 2 weeks, so I won't get to fly for a few weeks. Darn.