J-85 or an Iranian copy (Owj jet engine).
Just... no.
Can you think of any 3rd, 4th or 5th generation fighter that was modified to change engine configuration? I can only think of the F-20 Tigershark (Twin Engine F-5 made into single engine F-20), and even that never reached production, besides it was a conversion from twin engine to single, not the other way around.
Changing engine configuration is a huge task. You are changing the aircraft in a massively fundamental way. Basically all the internals have to be completely reworked, and a lot of the externals as well. Flight characteristics will change, in both positive and negative ways.
And this is the JF-17, which is a small aircraft. Its like trying to shoehorn a Chevy V8 into a Peugeot 206 (size-wise). There is simply no point. Much better to buy a twin engine aircraft from the start.
There is some evidence that Iran has already purchased SU-50. :::
Not an official poster. There is no evidence of Iran buying the Su-50.
Sorry but I'm now going to crush all speculation of Iran buying the JF-17.
Iran is
twice as big as Pakistan. Bigger country means you need longer ranged planes. The JF-17, as a small single engine aircraft, does
not have the required range for the role Iran requires, which is
air superiority. The JF-17 is meant to supplement the F-16 (even though the F-16 was actually designed as a light fighter).
Pakistan's enemy (India) borders Pakistan. Pakistan, therefore, does not require it's aircraft to have a long range to engage in offensive operations. Iran's accessible (I say accessible because I hardly expect Iran to go bombing Israel, that's what the ballistic missiles are for) enemies are across the Persian Gulf (Saudi and whoever decides to support it), and in the Gulf of Oman (US Navy). Iran needs long ranged aircraft to strike back at these adversaries.
As I already said, Iran desperately needs an air superiority fighter. The JF-17 is
not such an aircraft. It is a light fighter. As such it not only has low range but also low payload. Another vital thing required for Iran's needs. Furthermore, with Iran being mindful of its spending, it would prefer a multirole aircraft that can also strike enemy targets. While the JF-17 is multirole, its low payload again hampers its efficacy in such a role.
For sure, the JF-17 is probably more capable than almost all of Iran's fighters, bar the F-14. But we are not looking for replacements for the sake of replacements, we want replacements that fit our needs and requirements. The JF-17 does not do this.
An Su-30 would fit this role, though the future requires stealth aircraft.
Lastly, to the troll, fvck off.