I ran across this brief video shot inside of GM's wind tunnel,with Dr. Paul MacCready running a pitot-tube stethoscope across the cars body doing boundary layer whispering.
400-mpg according to MacCready, with modest otto-cycle power.
PS
*Sunraycer was reported at Cd 0.089 with original wheel fairings.
*In race form,without the fairings it was reported at Cd 0.125.
*GM Aerodynamics Laboratory has since downgraded some of their earlier coefficients of aerodynamic drag and now claims Cd 0.147.