And what does this energy in the form of heat get you? Nothing but design headaches. The energy is useless unless it is converted into thrust, by way of pressure. Pressure - also another way air holds energy. More exhaust temp does not necessarily mean more thrust. More pressure means more thrust. In fact, the heat leaving the engine in the exhaust is wasted energy, a by-product of heating the air to gain the pressure increase. A more efficient engine does a better job of converting heat into pressure.