  Working in the extended black hole thermodynamics where a dynamical
cosmological constant defines a thermodynamic pressure p, we study the
efficiency of heat engines that perform mechanical work via the pdV terms now
present in the First Law. Here the black hole itself is the working substance,
and we focus on a judiciously chosen engine cycle. We work in
Gauss-Bonnet-Einstein-Maxwell gravity with negative cosmological constant and,
using a high temperature expansion, compare the results for these `holographic'
heat engines to that of previously studied cases with no Gauss-Bonnet sector.
From the dual holographic large N field theory perspective, this amounts to
studying the effects of a class of 1/N corrections to the efficiency of the
cycle.
