"Gong said that the domestic engines unleashed the potential of the J-20, since the old engines were not customized for the aircraft, and it had to make compromises in its performance.

In addition to developing the engines, the J-20, including its airframe, structure, pipelines, electric circuits and subsystems, were redesigned, Gong said."

https://www.globaltimes.cn/page/202201/1246406.shtml