[cleanspeed1]

Typical auto trans equipped vehicle experiences 25-35 percent loss in the drivetrain because the transmission absorbs most of the power. Adding the overdrive adds weight and drag to the system ( the mfg can give the number )

BSFC before or after peak torque goes up substantially, but since each engine is different and the conditions it operates in vary, only testing will give an accurate number.

Going to a lower numerical gear with the stock combination will not make sense if you tow all the time, but boosting bottom end torque with a cam swap and a recalibration to keep the torque level the same with a lower numerical gear increases efficiency ( stock Metro vs Metro XFi as an example ).


I don't have to experiment with an OD unit; I own a Volvo Class 8 style expediter. Has a VED12 ( 335hp / 1300 ft/lbs of torque, 33000 GVWR ). Averages 9-11 mpg loaded @ 63-65 mph. Compared to a smaller engine straight truck ( 210hp/ 600 or so ft/lbs and 7-8L ), gets a good 2 mpg better. Why? More torque at a lower rpm with a more favorable bsfc. The torque band goes from 1100-1300 rpms, then falls off a cliff. Running the engine in this range gives the best mpg. 9 speeds with OD.

Your last question brought the reason for free wheeling hubs, parasitic losses. Since you clarified that you have a 2 WD that is a moot point.

I will emphasize again, since you are making it personal, I am going to keep it technical, and as far as jumping to conclusions, you've done the same.

You are trying to prove something beyond the machinery and the parameters around the question that were presented in the beginning. If it's going to make you feel better, then so be it. But in the end, it has not affected me one bit. I only have done what you are trying to do, just with much larger vehicles in gas and diesel, and with a much higher pricetag.