Originally Posted by
LivingInMEM
Saw one taking off today. I think the smoke trails certainly gave away the fact that the engines are the same.
The original "F" models were equipped with the TF33-P-11 engines with 16,000 lbs. of thrust. A change to the TF33-PW-7 (hundreds available from C-141s) would boost the thrust to 21,000 lbs. That's about 30% more thrust. NASA could also strap on the J60s used in the four engine configuration.
I don't think you observed the newly overhauled (modified) "F" unless they are up to test flight status and you live in Colorado.