It's all in that thread :) The 80% limit was only on one engine, due to vortex issues. The others had to be at "100%" and full afterburner to get off the ground. The actual volume of fuel flow for a particular power level was also determined by an analogue computer measuring the inlet air temperature and pressure.

http://www.pprune.org/tech-log/423988-concorde-question-4.ht...