Ignition retarding exhaust valve risks

[zoomzoom]

Ive now set up my own ignition retarding feature for when the auto transmission shifts under heavy load. I run about 13psi under full load, and I wondered what stresses are on the exhaust valve when the cylinders are being fired at 0 degrees advance. AFRs under full load are around 11.5 : 1. Should that keep the combustion temperature in a safe range for the valves? Or should I richen further while retarding the ignition?  The retarding period lasts about 200ms, or about 10-12 combustion events per cylinder at most.

[GTSBoy]

200 ms is nothing.  Worry not.