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A maximum jet efficiency line $R\sim 25$ ($R=L_{\rm jet}/L_{\rm bol}$), foundin FRII radio galaxies by Fernandes et al., was extended to cover the fullrange of jet power by Punsly. Recent general relativistic magnetohydrodynamic(GRMHD) simulations on jet formation mainly focused on the enhancement of jetpower. In this work, we suggest that the jet efficiency could be very high evenfor conventional jet power if the radiative efficiency of disk were muchsmaller. We adopt the model of a thin disk with magnetically driven winds toinvestigate the observational high efficiency jets in FRII radio galaxies. Itis found that the structure of a thin disk can be significantly altered by thefeedback of winds. The temperature of disk gradually decreases with increasingmagnetic field; the disk density, surface density and pressure also changeenormously. The lower temperature and higher surface density in inner diskresult in the rapid decrease of radiative efficiency. Thus, the jet efficiencyis greatly improved even the jet power is conventional. Our results can explainthe observations quite well. A theoretical maximum jet efficiency $R \sim 1000$suggested by our calculations is large enough to explain all the high jetefficiency in observations even considering the episodic activity of jets.

The high efficiency jets magnetically accelerated from a thin disk in powerful lobe-dominated FRII radio galaxies