[molotovbliss]

Tires, and a powerplant are two different domains. There's lots more at play with structure & what other parts can withstand. Resonance, materials, & aerodynamics all play a factor in the design process. Combine it with flying through the air in a seat instead of the ground, makes it all even more a factor.

Ever see Mazda Miatas with a Chevy LS motor? Kits are sold to adapt, especially now everything is drive by wire / software.

[macspoofing]

I understand your point, but this is the reality of modern aviation. New engines are released for existing airframes. In this case though, it wasn't an existing airframe. This was a new model built around new engines. Where the analogy starts to break down is that unlike putting new tires on, any face-lift that is done to an airliner is backed by testing and and under the watchful eye of multitudes of regulators.