[aerohead]

For Diesels,load doesn't seem to matter as much as for gasoline engines,as they have no throttle,however,pumping losses in the gasoline engine are pretty much governed by load and throttle position.Since the throttle plate has a drag coefficient of of 1.11(like a sheet of plywood),the BSFC maps usually show economy peaking in the range where torque peaks,which is where charging efficiency is peaking with best volumetric efficiency and the throttle plate is well "open".In olden days,some carburetors were designed such that at cruise,the primary butterfly valves were essentially wide-open,with minimum pumping losses.Your turbo idea may have much merit.If you choose to do the project,try and get a good baseline,then do a bunch of record keeping after the mods so we can all learn from your experiences.There's been much discussion over the years about turbos/mpg,this would be a great way to get some good numbers on this topic.