A stoichiometric compression ignition engine has a turbocharger coupled to it so that the exhaust from the engine feeds the turbine and the compressor provides combustion air past a throttle and intercooler to the engine intake manifold. An exhaust after treatment device is positioned before the exhaust of the engine. A power turbine is connected in parallel relation to the turbocharger turbine and is controlled by a valve to operate the power turbine whenever either the turbocharger compressor boost or the turbocharger turbine back pressure exceed given limits. The power turbine is connected by a power transmission device to either couple to the engine output or to an electrical generator. An EGR loop may be driven by a pump also connected to the power turbine to lower in cylinder pressures.