[DynoCobra]

Why are you using 16L engines? They are only needed in the Rocky Mountains. If you are thinking of aero ideas, then you first look smaller displacement engines like 12or 13L. Change final drive gearing to max speed versus engine torque needed to maintain speed on level ground with max load. When you get to that point, you can start fine tuning your aero and oil additives. I drove otr for years, was the top driver in my company for fuel mileage and built race cars and fuel economy vehicles that I drove for years. Took 1st place in the Iowa State Fuel Challenge getting 82.0 mpg from my VW diesel pickup in 1981. Subsequently I increased the mileage to 105 mpg as my daily driver by fine tuning with oil and aero adds. Btw, I averaged 7.2 mpg with my 13L 2009 Volvo 780 series.