I get 34mpg on highway with my ancient OM616 turbo in the Gurkha, that too on a all steel non aerodynamic body, not bad considering its just a mechanical pump with no fancy ECU or controls.

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99 Gurkha with OM616 IDI turbo

2015 Gurkha with OM616 DI turbo

2014 Rexton W with OM612 VGT