[serialk11r]

It'll be more efficient at high load if you can radically modify the cam profiles or have variable valve duration. A turbocharged "Atkinson" cycle engine is essentially a turbocompound engine (turbocharger takes over compression duties, cylinder is used more for expansion than compression).

The problem is with most engines, ANY boost even on high duration race cams is going to be more torque than you need to cruise.

You need VVEL/Valvematic/Valvetronic/Multiair to be able to cut volumetric efficiency enough, but at low load the exhaust has less waste energy and the engine's friction is the greatest source of loss so the improvement will be very minimal.