For the entire 455 flight hours on the IO-390 in my -14A, it turns out I?ve been using short reach spark plugs in long reach adapters that came with a P-Mag I installed on the new engine. These short reach plugs are recessed in the adapter about a half inch so their electrodes do not protrude into the combustion chamber at all.
Why this arrangement? Well, it was unintended. When I ordered a single P-Mag for the engine I specified an IO-390 and it came with long reach adapters because this engine uses long reach aviation spark plugs. Since no specific automotive plugs were recommended in the P-Mag manual but several different ones were said to work OK by P-Mag users, I simply bought the least expensive and installed them. It did not dawn on me at the time that those plugs (NGK BR8ES) were too short for the adapters.
In two words, their performance in this configuration has been ?ops normal?. They are inexpensive and all 4 get discarded each annual. There has been nothing irregular about this setup even though one would think the flame front would be in some way inhibited by virtue of the electrodes being ?captured? inside the adapter. I?ve operated everywhere from sea level to 18,000 feet at a wide range of temperatures, density altitudes and power settings and the aircraft and engine don?t seem to know the difference. CHT, EGT, lean of peak operation, engine smoothness, climb performance, speed versus power, fuel consumption and every other parameter I?ve seen have been normal and consistent with what other 14 owners report.
Will I now install the correct long reach plugs? Nope. My mission is long distance travel and these plugs have served me well. The more expensive long reach iridium plugs might produce another horsepower (or not) but I cannot believe such a change would make any significant difference.
Just a heads up as to my inadvertent experience.
Why this arrangement? Well, it was unintended. When I ordered a single P-Mag for the engine I specified an IO-390 and it came with long reach adapters because this engine uses long reach aviation spark plugs. Since no specific automotive plugs were recommended in the P-Mag manual but several different ones were said to work OK by P-Mag users, I simply bought the least expensive and installed them. It did not dawn on me at the time that those plugs (NGK BR8ES) were too short for the adapters.
In two words, their performance in this configuration has been ?ops normal?. They are inexpensive and all 4 get discarded each annual. There has been nothing irregular about this setup even though one would think the flame front would be in some way inhibited by virtue of the electrodes being ?captured? inside the adapter. I?ve operated everywhere from sea level to 18,000 feet at a wide range of temperatures, density altitudes and power settings and the aircraft and engine don?t seem to know the difference. CHT, EGT, lean of peak operation, engine smoothness, climb performance, speed versus power, fuel consumption and every other parameter I?ve seen have been normal and consistent with what other 14 owners report.
Will I now install the correct long reach plugs? Nope. My mission is long distance travel and these plugs have served me well. The more expensive long reach iridium plugs might produce another horsepower (or not) but I cannot believe such a change would make any significant difference.
Just a heads up as to my inadvertent experience.