Well there's only so much you can do to an existing design before you reach it's technical limit. They may have implemented some ideas from OT (OverTechnology) to get a slightly more effecient engine. Or it could be something like getting the F-14 up to spec of current fighters is use. Probably at this point in the war, they've lost lots of fighters. They have lots of older fighters that could still be used. But considering that they used technology which is 10-20 years old by that time, they need to bring those fighters up to the level that their current fighters were at.
It could be like taking an early 1980s car and modifying the insides of the car to bring it up to an equivalent car of today without changing the look of the car (i.e., no body kits, no lowering, etc). IMO, that's what the F-14s in M0 are.
Yeah. I figured Starscream was actually a tad of a stretch.
But hypothetically, the insides of the jet could be all new with only the frame being the same, if I'm not mistaken.
That'd be a LOT diffrent than a standard F-14.
Obviously your ultimate limit is the stress the frame can take, though that limit might can be bypassed with overtech energy armor like the VFs have. Depends on how exactly it works.
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I guess that WOULD be bringing the F-14 up to modern spec.