PAK FA was expected to use 5th generation engine custom-built for Russia’s fifth-generation T-50 jet fighters. But it is unlikely, Igor Korotchenko says:
"The engine used by the jet fighters will not meet the needs of the Sukhoi PAK FA. These are the engines of completely different types. A new engine should be developed from scratch, possibly, using technological advantages of the Tupolev Tu-160. The engine generates a larger thrust and has a complex automation system, to facilitate a number of flight modes such as maneuverability. It is expected that each engine will be able to independently vector its thrust upwards, downward or side to side. Vectoring one engine up with the other one down can produce a twisting force."
The new jet fighter will combine the advantages of the Tupolev-160 and of modern stealth technologies, including the 5th generation radio electronic systems, airborne radar facilities, and the arrangement of the flight deck.
That speaks volume about when the 5th gen engine may be ready. The current engine lacks both in next generation performance and stealth.