The key is that with two plugs, the combustion _in the cylinder_ is more
complete, earlier. When one mag cuts, the fuel air mixture still fully
burns, but the burn is continued slightly latter (where it does less work on

I can confirm that an engine running on one mag will show a higher EGT than on
both mags.

I went through the preflight, run-up, took off and during full-power climbout,
I noticed a significantly higher EGT than I was used to.

Startled me until I discovered that in the pre-takeoff mag check I had left the
mag switch on only one mag - I took off and was climbing on a single mag. Duh!

Switching to both mags brought the EGT back down to normal.