Cessna 185 Performance and Test Data 1978 C185F N8383Q 7 February 2006 IO520 vs. IO550 GAMI Injectors Hartzell 80” 3-blade “Top Prop” ROP = Rich of Peak LOP = Lean of Peak WOT = Wide Open Throttle ROP OPERATION CHT/EGT (520) 24” x 2400rpm 15.0gph 154mph 362/1375 (550) 24” x 2400rpm 18.0gph 174mph (520) 24” x 2275rpm 15.0gph 150mph 365/1308 (550) 24” x 2275rpm 16.0gph 163mph LOP OPERATION (520) WOT x 2400rpm 14.5gph 163mph 365/1410 (550) WOT x 2350rpm 14.5gph 168mph 288/1332 (averaged) (550) WOT x 2400rpm 15.0gph 172mph 293/1342 (averaged) (550) WOT x 2350rpm 16.0gph 178mph 321/1390 (averaged) N8383Q 1978 C185F IO550 w/GAMI injectors EI UBG-16 engine analyzer EI FP-5 fuel flow gauge 19 October 2007 N8383Q 1978 C185F IO550 w/GAMI injectors EI UBG-16 engine analyzer EI FP-5 fuel flow gauge The following techniques produce the best speed, the lowest fuel flow and coolest operating temperatures in my airplane. (I had similar results with the original IO520, though speeds were at least 5 mph lower). I fly wide-open-throttle (WOT) and lean-of-peak (LOP), even for short flights at low altitudes. At takeoff, use full throttle and full rpm (2700), full rich mixture (should indicate at least 27gph fuel flow). Cowl flaps wide open. Maintain during initial climb, about 500’ to 1000’. After initial climb, establish about 120mph; leave throttle wide open, reduce rpm’s to about 2400, then quickly reduce fuel flow to about 14.5gpm (LOP), close cowl flaps (leave open on warm days, say above 70 degrees). Again, leave throttle wide open. Once at cruise altitude and speed, close cowl flaps and monitor EGT’s and CHT’s. If EGT’s approach the limits I have established for my plane, lean slightly or open the cowl flaps a bit; if EGT’s and CHT’s are below limits, enrich mixture slightly. I will say it again, throttle should be wide open. (I know, I thought the same thing, but it works). About a minute prior to setting up approach I fully open the cowl flaps to begin cooling the engine. Then, just prior to reducing throttle, I close the cowl flaps. I reduce power, leaving rpm’s and mixture at cruise settings until final approach speed is established, then prop control and mixture control go full forward. This allows the engine to cool slowly, with no “shock cooling”. EGT limits: I run 50 degrees below peak EGT when LOP (peaks as determined when running the GAMI lean test). CHT limits: I use 380F as the limit for CHT’s. In LOP cruise CHT’s will be about 340F, and 4 cylinders will often be within 1 or 2 degrees of each other; all are within 10F or 15F of each other. If CHT’s get close to 380F lean a bit and/or open cowl flaps. EGT’s and CHT’s will rise dramatically if the throttle is reduced, even a little bit, from WOT; I have found this helpful in keeping the CHT’s above 300F during cold winter flying, but I always fly WOT otherwise. On 3450 floats I cruise at 140-145mph, flow 14.3-14.6gph. On wheels I cruise at 160mph with the same fuel flow. Several local friends with 185’s have learned to fly this technique and all have experienced similar results. GAMI injectors will keep the engine running smooth while running LOP; 6-probe digital EGT and CHT are a must. I resisted the digital fuel flow for a few years, but now I realize it is also a must for accurate fine tuning (my analog fuel flow gauge reads at least 1 gph high); in addition, I know precisely how much usable fuel I have in the tanks. About once a year I say to myself “this is too good to be true”; I pull the power back to 24 square, the plane slows about 8mph, I open the cowl flaps to keep temps within limits, and fuel flow goes up 1.5gph. A good resource for the theory behind LOP operation is available in John Deakin’s articles on “Pelicans Perch”, available through a link on avweb.com (in addition to his tales about flying a Huricane, how to manage engines on a Super Connie, gear-up landing a 747, FL30 in his Bonanza……). One of his best for LOP operations is titled “Putting it all Together”. GAMI will readily answer questions as you gather operating data for your engine. 
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