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Another way to reduce pumping losses is by carefully increasing the EGR rate (for engines with external EGR) at part load so that a larger throttle opening can be used for a given torque output. Cooling the EGR with a water-cooled heat exchanger works better because reduces heating of the intake charge (most modern diesels have EGR coolers). This is part of what Toyota did (along with Atkinson Cycle) in order to achieve 40% brake thermal efficiency on the new 2018 2.5L non-HEV version of the Camry, but the basic idea has been well known for years. It also changes combustion phasing, so having access to reflash the ECU to change spark timing is essential. At very light loads, residual can also be increased by changing valve overlap on engines with VVT and can also reduce pumping losses, but it also increases charge temperature. Some versions of VTEC should allow you to do this.
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