rjcthree
Well Known Member
I’m observing some behavior that I would like the group’s opinion on.
Setup: O-320-H2AD, 33H Hobbs/19.5H Tach since OH with new cam, lifters, new Lyc cylinders. Ellison, standard dual mag (D3000) also OH. Sensenich fixed, RV-9A. Compressions are 76/80 or better cold.
At full throttle/WOT – 28.5in HG for the most recent flight - at low altitudes (takeoff), CHT and EGT’s line up well. EGT’s are in the 1250F average range for what it’s worth, all rich of peak. At MP’s slightly below WOT to medium throttle – 27in HG to 20 in HG– cylinder #4 EGT falls by 100F-150F and CHT for #4 falls by about 30F-40F versus the average of the other three. The EGT falls fast and settles out with thirty seconds, CHT takes a couple minutes. Below 20in HG, all four cylinders come back together again in EGT and CHT quickly. It is repeatable, centering around 20in HG MP.
There really isn’t any perceived roughness, and even in this 27in - 20in HG cold-cylinder range, #4 EGT and CHT responds normally and consistently with the other cylinders to leaning, they are just doing so from a significantly different place. Since I lean to basically 100F-150F ROP at anything less than WOT, I can’t say if ranging from full rich to lean changes the behavior at the transition points. I believe it’s been occurring since hour 1.5 based on the data (no high power data exists prior to this time, <1.5H is all run-in), and there is no significant metal in the first two oil changes, suggesting I’m not wiping a lobe.
My first suspect is ignition, looking for one side of the ignition falling off on #4. I have not done any disassembly inspection yet, only gross inspection of the ignition harness - no obvious ignition leakage or damage to plug wires, and timing is on target. I did check the intake tube clamps (thanks Ralph, I should have mentioned it).
My plan: Run the Savvy ignition test in flight, in various levels of richness/leanness and MP’s. If it’s ignition, I expect it will show up pretty clearly, and the diagnostic work from there is (hopefully) logical: plugs, harness and magneto get the focus. I’ll probably look at the plugs anyway – a cylinder running that cold may be generating deposits that may point at something (one plug not firing being scuzzy?).
If that doesn’t give any hints, I will confirm my secondary elements: valve lift, boroscope, pushrods.
Any hints or past experience would be welcome. Thanks.
Setup: O-320-H2AD, 33H Hobbs/19.5H Tach since OH with new cam, lifters, new Lyc cylinders. Ellison, standard dual mag (D3000) also OH. Sensenich fixed, RV-9A. Compressions are 76/80 or better cold.
At full throttle/WOT – 28.5in HG for the most recent flight - at low altitudes (takeoff), CHT and EGT’s line up well. EGT’s are in the 1250F average range for what it’s worth, all rich of peak. At MP’s slightly below WOT to medium throttle – 27in HG to 20 in HG– cylinder #4 EGT falls by 100F-150F and CHT for #4 falls by about 30F-40F versus the average of the other three. The EGT falls fast and settles out with thirty seconds, CHT takes a couple minutes. Below 20in HG, all four cylinders come back together again in EGT and CHT quickly. It is repeatable, centering around 20in HG MP.
There really isn’t any perceived roughness, and even in this 27in - 20in HG cold-cylinder range, #4 EGT and CHT responds normally and consistently with the other cylinders to leaning, they are just doing so from a significantly different place. Since I lean to basically 100F-150F ROP at anything less than WOT, I can’t say if ranging from full rich to lean changes the behavior at the transition points. I believe it’s been occurring since hour 1.5 based on the data (no high power data exists prior to this time, <1.5H is all run-in), and there is no significant metal in the first two oil changes, suggesting I’m not wiping a lobe.
My first suspect is ignition, looking for one side of the ignition falling off on #4. I have not done any disassembly inspection yet, only gross inspection of the ignition harness - no obvious ignition leakage or damage to plug wires, and timing is on target. I did check the intake tube clamps (thanks Ralph, I should have mentioned it).
My plan: Run the Savvy ignition test in flight, in various levels of richness/leanness and MP’s. If it’s ignition, I expect it will show up pretty clearly, and the diagnostic work from there is (hopefully) logical: plugs, harness and magneto get the focus. I’ll probably look at the plugs anyway – a cylinder running that cold may be generating deposits that may point at something (one plug not firing being scuzzy?).
If that doesn’t give any hints, I will confirm my secondary elements: valve lift, boroscope, pushrods.
Any hints or past experience would be welcome. Thanks.
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