The standard equations for mass momentum and energy can be used to provide an estimate of the losses in total pressure as energy is added to a one dimensional flow. These losses are taken into account when the most basic performance model for the ramjet engine is extended to provide performance figures for the scramjet engine. Another eject { more pronounced in the scramjet than in the ramjet { is the choking of the engine as heat is added. It is shown that these two eects quite substantially reduce the thrust of the scramjet engine, something which underlines the importance to reduce all other sources of losses connected to the scramjet engine; e.g., losses connected to the intake and friction losses in the combustor.