vlittle
Well Known Member
I'm seeking the answer from knowledgable engine guys for the following observed operation of my engine: O-320, Superior roller lifter crankcase, ECI cylinders, dual Slick mags:
Right from the beginning, this engine has run well with plenty of power. After 106 hours, I checked the timing (I did not check when the engine was new). I found that one mag was about 35 degrees BTDD and the other about 30 BTDC.
I adjusted both to 25 BTDC.
Before adjusting, I could run the engine well lean of peak with no roughness, only an RPM drop off as it got very lean. Now, there is a very distinct point of roughness as I pass peak EGT.
This is not a problem, but it got me thinking: why was it so smooth when the mags were mis-timed? I have my theories, but I'm not an engine guy.
My guess is:
Since the timing was so advanced, it gave the lean fuel/air mixture more time to burn completely in the combustion chamber, thus reducing lean misfire. I always tried to run 55%-65% lean 'best economy' or LOP (when I could), and watched my CHTs for temperature spiking... never saw anything that could indicate detonation.
Perhaps this is why electronic ignitions seem to be better for LOP operation... they advance the timing. If this is the case, it's not a function of having electronic ignition per se... it's just the spark timing that allows LOP.
Any experts out there with an explanation?
Right from the beginning, this engine has run well with plenty of power. After 106 hours, I checked the timing (I did not check when the engine was new). I found that one mag was about 35 degrees BTDD and the other about 30 BTDC.
I adjusted both to 25 BTDC.
Before adjusting, I could run the engine well lean of peak with no roughness, only an RPM drop off as it got very lean. Now, there is a very distinct point of roughness as I pass peak EGT.
This is not a problem, but it got me thinking: why was it so smooth when the mags were mis-timed? I have my theories, but I'm not an engine guy.
My guess is:
Since the timing was so advanced, it gave the lean fuel/air mixture more time to burn completely in the combustion chamber, thus reducing lean misfire. I always tried to run 55%-65% lean 'best economy' or LOP (when I could), and watched my CHTs for temperature spiking... never saw anything that could indicate detonation.
Perhaps this is why electronic ignitions seem to be better for LOP operation... they advance the timing. If this is the case, it's not a function of having electronic ignition per se... it's just the spark timing that allows LOP.
Any experts out there with an explanation?