As I understand it, FSX program started in 1987 when it was decided to replace F-1 with a new aircraft based on F-16A with 25% larger wing area. Maiden flight was in 1995 and it was not until 2000 that F-2 entered service. With all the money and engineering resources of Japan, it took 13 years.
F-2 uses the US F110-GE 129 engine with 75.62 KN dry thrust. Since normal loaded weight of F-2 is 33,000 lbs, even with after burner T/W ration is 0.89. Making F-2 under powered compared to most modern fighters where T/w ratio is close to 1.
Initial idea was to produce an aircraft cheaper than F-15, but the result was an aircraft which was as expensive ( $129-million in 2009 dollars) as F-15 but far less capable. Therefore numbers of planned units were reduced from nearly 140 to 94.Pakistan has neither the resources nor the time to take up such ambitious projects.
http://www.defenseindustrydaily.com/lockheed-mitsubishis-f2-fighter-partnership-03188/
Japan - It's A Wonderful Rife: Mitsubishi F2 Fighter Jet
Larger airframe means increased weight requiring more powerful engine. Getting the more thrust from the same size engine is an extremely difficult problem to surmount because high temperatures and high pressure required inside the turbine raise reliability issues. It is precisely why there are only a handful of countries with the capability to produce trust worthy high performance aircraft engines. US & Russia being the leaders followed by UK, France & now China.
This is evident from the fact that JF-17 uses Russian RD-93 engine, Swedish Grippen uses licence produce GE-F404 produced by Volvo; HAL Tejas is also powered by GE-F404. Even the Korean T5- Golden Eagle is powered by Ge- F404. Chinese WS-9 engine was licensed version of Rolls Royce RB.168. WS 10 Engines are indigenous but untried. Understand that even one of the J-20 prototypes is being tested with the Russian AL-31.
Therefore even after going thru the effort of redesigning the Thunder airframe with larger wing area, power plant will remain a big problem. We have seen that happening with HAL Tejas!
Finally, how can we forget that JF-17 was not developed by Pakistan alone but with huge input from China? Pakistan on its own has neither the resources nor the technical know-how to start such program on her own; would China agree to jointly develop a larger & heavier JF-17 when she is already heavily involved in J-20 & J-31 programs?
I have every respect for honourable Mastan Khan and this post is not meant for ‘pooh poohing’ the idea. I am however a trained engineer and look at all things with a practical point of view.
In addition to onerous program cost and time lag, no suitable power plant may be available / accessible to Pakistan and without the guarantee that the new aircraft will be better than off the shelf options such as buying additional F-16’s or J-20 etc.; in my opinion this idea is not “Practicable”.