My IV has dual batteries and alternators and lots of sound deadening in the floor and so has empty weight of 1984 lbs.  

 

The IO-550N (kinda sorta) has stock 8.5 compression, one electronic ignition, one magneto and gains about 1.5-1.7 in. Hg in manifold pressure due to ram pressure effect and modified cooling air inlets and outlets. 

 

I most commonly fly 8500-9500 feet, 30F above standard atmospheric temperature, 65% LOP 13.5 GPH (per MVP 50 engine monitor), and get 220 knots at mid weight, a trifle less at gross (3200) and a bit better when light.  At 8500 feet, full throttle, 2700 RPM, best power mixture which would be max cruise speed, figure 235-240 at mid weight, but burning about 35% more fuel, so I never do it since fuel is about USD $8-9 per gallon here in Australia.  The airplane is a bit buggy and dirty at those conditions which is typical for my cross continent trips.

 

Keep in mind that I spent a LOT of effort on cooling drag reduction with cowl flaps, careful inlet and outlet redesign and such which reduced total aircraft drag area about 10% which translates to about 3% more speed at the same power.  (And it runs way too cool, sub 300F CHT.)  But I tend to slow down and use the drag reduction to reduce fuel burn.   I have operated out of 2600 feet of hard pack grass at mid weight (2750 lbs) and did so today for a small fly in, but margins were mighty skinny with no head wind and low trees at the end of the farm country runway and ground still damp from recent rains.   At my home drome of 4100 feet paved, I have no problem turning off at 3000 feet in zero wind.  Secret: meticulous attention to the angle of attack indicator the last mile to touchdown, and thump it on with some power still on.

 

Fred Moreno