I recently purchased a two channel  portable wideband O2 system and installed bungs and plugs on each exhaust runner. I also have a downstream wideband that I have been using for several years. I was able to spend a very productive hour ground tuning and adjusting Mode 4 injector balance prior to my flight yesterday from Austin to Akron OH. I’m not sure what to make of the F/A EGT spread data I collect during yesterday’s flight.

During the ground tuning session I balanced rotor 1 to match rotor 2 using F/A ratios for takeoff condition. This produced very close EGT readings. However at my preferred cruise settings I’m seeing a large EGT spread. I would expect a consistent EGT ratio change when adjusting the mixture knob at a steady rpm / MP.  This appears not to be the case. What am I missing?

Bobby Hughes