They have talked for years about re-engining the B-52 with something more modern than its TF33-P-3/JT3D turbofans, which are fairly low-bypass (1.42:1 for the JT3D).
Modern engines are much higher bypass - like the GE Passport at 5.6:1, similar to the CF34 - in the same weight class and thrust as the TF33. A larger engine like the LEAP has an even higher bypass ratio, e.g. 11:1.
Now, the B-52 has a published operating ceiling of 50,000 feet. The 737, A320, Bombardier RJs etc. have a ceiling of 41,000.
However the KC-135s, re-engined with semi-modern CFM56 high-bypass turbofans, have a ceiling of 50,000 feet.
So I am confused. Does the bypass ratio have an impact on the practical ceiling of the aircraft? Could the B-52 fly to current spec with engines like the GE Passport?
A side question... the TF33 claims a specific fuel consumption of 0.56 lb(lbf-h). I can't seem to find that figure on the most recent high-bypass turbofans. Is it inapplicable to high-bypass turbofans? If not, is there a viable way to figure what a modern engine would do to the B-52's range?