Saw this as an ad on YouTube today. What engine do you think should be the retrofit engine? Whatever the military equivalent to the JT8D is what they already have, in my opinion be replaced by GeNX engines, 4 GeNX engines provide just as much power as JT8Ds and reliability of jet engines has improved over time.
I would venture to guess it will be the CF6. but this conversion of the engines would be a long time running as you are redoing a critical aspect of an aircraft. That’s not that easy to do. If it was you’d see airlines just do a simple engine upgrade on older air frames. It would be a neo of sorts but instead of making a redesign of a former aircraft and starting to rebuild the air frame they have to make the engines fit with the current air frame with minor modifications.
You have a point, but very low by-pass engines aren’t efficient, so they would need bigger engines, maybe not a GEnx, CF6 or Leap. I really don’t have a clue, but I thought that developing a new engine wouldn’t be cost effective. If P&W, GE, RR develop that engine, they would need to use it elsewhere, or a limited 4-6-8* engines for ~76 (+spare engines) jets wouldn’t give the necessary financial return
No matter what your budget is, nobody wants to piss away billions of dollars if they can prevent it. In this case, in the long run, it will save a few billion so it makes sense for them to do the upgrade.