The problem is you are comparing the cruise TSFC of one engine to the takeoff TSFC of another, most high bypass engine around at the moment have a TSFC of 0.3-0.4 at takeoff, and 0.5-0.6 in cruise.
During takeoff the thrust being produced is higher, so even with a lower TSFC than cruise, the amount of fuel being consumed is greater.
When comparing engines, you also need to take into account the mass of the engine, the speed and altitude of the aircraft as this will effect the efficiency of the engine.
RB211-524H-T - TSFC is closer to 0.56 in cruise, generating 11,813 lb thrust at 35,000 ft, M0.80
PW4060 - TSFC is closer to 0.58 in cruise, generating 12,000 lb thrust at 35,000 ft, M0.80
CF6-80C2B6 - TSFC is closer to 0.564 in cruise , generating 12,000 lb thrust at 35,000 ft, M0.80
RB211-524H-T - TSFC is closer to 0.35 at takeoff
PW4060 - TSFC is closer to 0.365 at takeoff
CF6-80C2B6 - TSFC is closer to 0.348 at takeoff
RB211-524H-T - dry weight 9,470 lb
PW4060 - dry weight 9,213 lb
CF6-80C2B6 - dry weight 9,670 lb
The RB211-524H-T (60,600 lb), PW4060 (60,000 lb), and CF6-80C2B6 (60,800 lb) are all 60 klb engines used on the 763ER.
Looking at the numbers above the CF6 and RB211 are fairly close, with PW
having the to carry about an extra 900 lb for the engines alone over a CF6, and more fuel efficient.
The part of the equation that we do not know, is the purchase price and maintenance costs for the engines. With jet fuel today at 2.055 US$/US gal (todays quote from IATA) it would still be possible to put a pair of PW
power plants on a 763ER and still come out with a overall lower cost of ownership over the lower fuel burning competitors.
[Edited 2007-08-31 19:14:42]
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