Emirates Airline wants the proposed General Electric (GE) GE9X engines for the Boeing 777X to provide even more thrust for the aircraft than originally planned, to reach sufficient performance levels in Dubai’s extremely hot summers.

“The extra thrust is needed to compensate for the cancellation of the water injection system,” Emirates President Tim Clark tells Aviation Week. The increased power requirement “applies to both variants”—the 777-8X and -9X.

Emirates is expected to place a major order for the 777X at the Dubai air show later this month, most likely along with the other two large Persian Gulf carriers Etihad Airways and Qatar Airways.

The only airline that has already committed to buying the aircraft is Lufthansa. The German carrier, which does not have the same thrust requirements as Emirates, has been outspoken in its criticism of aircraft manufacturers tending to over-design new aircraft to meet the extreme performance requirements of just a few customers that will make the types less economical to operate for the rest of the market.

The GE9X, originally targeted at the “100,000-lb.”-thrust range, is understood to have had its thrust increased to as much as 105,000 lb. in response to Emirates’ demands. GE declines to comment on the thrust growth and says the company “continues to work with Boeing to ensure we meet the thrust requirements for the airframe.”

Although firm definition is still two years away, Boeing and GE have been working to meet the extreme range and payload requirements of the targeted Persian Gulf airline launch customers without over-engineering the 777X for the rest of the market. Nonetheless, Boeing is aware that by raising the bar on the performance targets for hot temperatures and ultra-long routes, the design will bracket a broader range of operator requirements in other markets.

As a result, Boeing is thought to have increased the 407-seat 777-9X’s range to beyond 8,100 nm. by increasing maximum takeoff weight (MTOW) to 775,000 lb. The shorter-bodied 777-8X, seating around 350 in a three-class arrangement, is targeted at the same MTOW.

GE’s challenge is how to retain the GE9X’s design advantage of a 10% lower specific fuel consumption (SFC) over the GE90-115B—which powers the long-range versions of the current 777 family—despite the creeping increase in takeoff thrust. The baseline configuration of the engine is therefore unlikely to differ much from that already disclosed, namely the advanced core, larger fan and suite of upgraded materials.

The first full engine is due to begin tests in mid-2016, but the initial run of the GE9X core is set for the second quarter of 2015. Flight tests on GE’s flying testbed are due to begin in 2017, paving the way for service entry of the 777X in 2020.

Tests of a 90% scaled version of the new compressor have been conducted on a rig at GE’s Oil and Gas site in Massa, Italy. The results of the evaluation are being used to fine-tune the design, which incorporates five combined bladed-disk or blisk stages, and prepare for runs of a second compressor in 2014.