WrightSpeed converted a USDM NPR to full electric several years ago. Integrating a highly tuned and efficient diesel engine of about 2.0 liters in displacement that produces 150 - 200 HP and 250 - 300 foot pounds of torque, into the system provides ample power in stand alone mode, when coupled to the electric drive or in a generator mode, only acting to recharge the battery bank, which is one of the things that diesel engines are good at doing, steady state work at peak efficiency.
Keeping the OEM 1250 pound engine and 350 pound automatic transmission is a poor choice, especially for it's 200 HP and 350 - 400 foot pounds of torque. Electric motors are excellent choices for high torque applications and are many times more efficient than gasoline or diesel engines, up to 96% efficient with current technology. I would readily swap the weight of the stock 1600 pound driveline for lithium batteries and a small diesel engine/generator.
Integrating a LiFeO4 or similar battery bank, into a new diesel driveline, BMS, ECM, TCM and motor controllers, then designing a "hybrid control" system of sorts to make it all work together, is a massive undertaking. Unless you have a PhD in Electrical Engineering, this is not a DIY project. OEM's spend billions of dollars and many years of R&D on this type of development. When Chevy gas V8s are a few thousand dollars in bulk and readily taken up by NPR buyers, Fuso and Isuzu will continue to buy them from GM for as long as they can. Diesel engines, in contrast, are heavy, expensive and complex with all of the modern emissions crap that serves to saddle the owner with additional maintenance and expense, while reducing fuel economy to the point where the emissions savings are nearly moot, are not the best choice when the big picture is taken in to account.
Isuzu and Fuso are well behind the domestic truck manufacturers, i.e. Yank Tanks, per the Aussie slang, but Ford, GM and Fiat Chrysler have dumped massive resources into hybrid and electric drivetrains over the last few years, while Isuzu and Fuso are offering trucks with 1990s interiors and electronics packages, sans 1990s transfer case. The cabover manufacturers are well and truly behind the curve in many respects and if they hope to make progress in the domestic truck market, have a long road ahead. Developing a hybrid or electric vehicle platform could help them to make up some of this ground.
