Jetdriver Posted August 12 Report Posted August 12 A quick question for those of you who have more experience with this than me. I have been experimenting with LOP/ROP operations in my M20F. I live in Utah so I am normally cruising between 8-12k. When I run 25° LOP I end up with almost 100° difference between my highest and lowest EGT (1400 vs 1300). When I run 100° ROP my EGTs are usually within 10° of each other (1250-1270). Is this normal?
Ragsf15e Posted August 12 Report Posted August 12 1 hour ago, Jetdriver said: A quick question for those of you who have more experience with this than me. I have been experimenting with LOP/ROP operations in my M20F. I live in Utah so I am normally cruising between 8-12k. When I run 25° LOP I end up with almost 100° difference between my highest and lowest EGT (1400 vs 1300). When I run 100° ROP my EGTs are usually within 10° of each other (1250-1270). Is this normal? It more depends on how far each is from peak. They should all be around 10-50 degrees lean of their individual peak egt, no matter what their actual numbers are. You will find that egts fall quickly on the lean side of peak, so that split is possible, especially if you don’t have even fuel distribution . What is your gami spread? This is the number of gallons ff you lean between when the first cylinder hits peak egt and tge last hits peak egt. Less than 0.5 is good. Another thought, I flew my F at the same altitudes as you because I’m up in Washington. Peak EGT works well at those altitudes and is not too warm. As long as you are below 75%, which you will be at those altitudes, even with full throttle, peak will work fine and not lose as much airspeed. To get to “peak”, I normally leaned until all 4 cylinders hit peak and then set ff so the last to peak was right at or just slightly lean of peak. 1
podair Posted August 15 Report Posted August 15 On 8/12/2025 at 8:05 PM, Ragsf15e said: It more depends on how far each is from peak. They should all be around 10-50 degrees lean of their individual peak egt, no matter what their actual numbers are. You will find that egts fall quickly on the lean side of peak, so that split is possible, especially if you don’t have even fuel distribution . What is your gami spread? This is the number of gallons ff you lean between when the first cylinder hits peak egt and tge last hits peak egt. Less than 0.5 is good. Another thought, I flew my F at the same altitudes as you because I’m up in Washington. Peak EGT works well at those altitudes and is not too warm. As long as you are below 75%, which you will be at those altitudes, even with full throttle, peak will work fine and not lose as much airspeed. To get to “peak”, I normally leaned until all 4 cylinders hit peak and then set ff so the last to peak was right at or just slightly lean of peak. I do exactly the same. Aim for Peak EGT,normally cruise 8k-10k , I will get systematically 143ktas on 33-34 litres an hour (8.5 us gph) with a stock 1967 M20F with three blade harzell. 2500rpm full throttle, map around 21 22. Those settings have served me well over 1800hrs and 17 years. CHTs around 340. Trying a bit more lop I lose quite a bit of speed, more rop the CHTs go up so does the flow obviously, not worth it for 4ktmore max. 2
MikeOH Posted August 15 Report Posted August 15 Another vote for WOT, 2500 rpm, peak, 8.5-9.0 gph when above 8K. I also see 143 ktas. I wouldn't worry about the LOP EGT spread. 1
Bartman Posted August 16 Report Posted August 16 Above 8K I fly at peak and you cannot hurt it at that altitude with the mixture. My EGTs are closer together while ROP but they peak individually at much wider spread and this will definitely affect the reading while 25LOP. Assuming both mags, wires and plugs are performing nominally, and the injectors are clean, the absolute EGT numbers do not matter. I aim for 10 LOP at lower altitudes. As previously stuggested, try to get the fuel flow from first to peak to last to peak as close to 0.0 as possible. 0.5gph will likely run well, but the closer your spread the smoother it can potentially run while LOP and also generate optimal HP. If one or two are very lean compared to the others, you will give up more HP while LOP and it does drop off quickly. We swapped out the injectors for the highest and lowest fuel flow and went from 0.5 to 0.2 consistently and often they peak simultaneously. I am also happy with 143kts @ 8.6gph and 2450. Can easily see 155 while ROP, but it’s not worth it to me. 2
Greg_D Posted August 16 Report Posted August 16 On 8/12/2025 at 11:44 AM, Jetdriver said: A quick question for those of you who have more experience with this than me. I have been experimenting with LOP/ROP operations in my M20F. I live in Utah so I am normally cruising between 8-12k. When I run 25° LOP I end up with almost 100° difference between my highest and lowest EGT (1400 vs 1300). When I run 100° ROP my EGTs are usually within 10° of each other (1250-1270). Is this normal? Have you done a Gami lean test? If so, what was the FF difference between the 1st and the last to peak?
Recommended Posts