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on 2/12/03 10:41 PM, [EMAIL PROTECTED] at [EMAIL PROTECTED] wrote: >> [EMAIL PROTECTED] writes: >> >> My question is what is the horsepower of this engine? > Due to the physics of fixed pitch props, it won't produce more cruise power > than an unmodified engine at the same RPM with the same prop in the same > airframe. It will produce more power in climb, but since climb power is > considerably below red line, it'll likely still be less than 85 hp. > The eye may be on the wrong ball here. No argument that turning a given prop at a given rpm yields identical results in climb and speed from identical horsepower. You very seldom actually get 85 hp from a 85 hp (operate at that narrow point on the power curve). What we really want to know is whether this modified engine is capable of significantly increased performance, and Continental power curves clearly show that it is. More displacement and higher compression result in more power available to apply throughout the operational range of the powerplant. Takeoff is, for the engine, a process beginning at maximum static rpm (and resulting horsepower) where initial acceleration is proportional to the increasing power and rpm. So find static rpm on the sea level C-85 power curve and write it down. The STC engine, with more power available to spin the same prop, will achieve a higher maximum static rpm. Find that rpm on the C-90 power curve and write that down. The difference in horsepower thusly derived and translated to a percentage is the advantage the STC engine will enjoy over the standard one as the takeoff roll begins. It is highly probable that much, if not all of such percentile performance advantage follows increasing rpms to and even beyond the 2575 redline of the C-85, whereas the C-85 will only reach 2575 rpm in cruise with a cruise prop (and reduced takeoff performance). Legalities aside, the mechanicals should be safe up to the 2750 maximum rpm approved for 0-200 continuous power if it could get there (it won't). The real advantage to increased available takeoff performance is with a full load at high density altitude. The extra displacement and more efficient (higher) compression ratio translates to valuable extra power whenever and wherever the standard engine's capabilities are sorely strained. If one throttles the STC unit back to where a standard C-85 could keep up, I'd bet this engine/prop/cam combination is more fuel-efficient at that hp and speed due to its higher compression ratio! It might also out-perform the O-200 STC because props tend to be more efficient at lower rpm for the same hp (long discussions with Fred Weick on this!). Any takers? WRB ========================================================================== ==== To leave this forum go to: http://ercoupers.com/lists.htm Search the archives on http://escribe.com/aviation/coupers-tech/
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