lightweight driveshafts

A lighter drive shaft will do very little for MPG. Once your going a steady speed, weight has almost nothing to do with MPG. Less rotating weight means faster acceleration (probably not enough to even notice), but if you accelerate faster, then you're using the same amount of fuel.

I have a carbon fiber drive shaft in my drag car, along with an aluminum fly wheel, light weight crankshaft, etc. All in the name of acceleration. The drive shaft was about $1500, a steel shaft costs about $300. They do make them from heavy trucks, but not for MPG. It more for stop & go applications like garbage trucks. It's more about reducing vibration and shock loads to rears.

Aluminum works too, but they are HUGE. Corrosion is a concern as well as wearing out U-joint bores. They do not last as long, 1000 HP mustangs don't drive is bad weather and don't get a million miles on them.

Think of it this way. You will not save fuel from less rotating weight unless you are very careful to accelerate at the exact same rate as before the lighter shaft, which you will not be able to do. Even if you could, the saving would be too small to notice. Once up to speed, the only advantage is 100 lbs less weight (of you don't add 100 lbs of freight) because rotating weight only makes a difference when it's accelerating. What is your MPG running 80,000 lbs? Now what is it running 79,900 on the same route? Not a measurable difference I'll bet.

 

Once again, a 1000 horsepower mustang will only have max 400 torque being put out, even if it's a jolt at start it compares nothing to 1500-2000 torque smashing 80,000lbs down a road.

 

My Camaro dynoed at 1276 HP and 1176 ft/lbs at the flywheel. Considering a 3.28:1 1st gear ratio, that's 3857.28 ft/lbs through the drive shaft, not including the shock load of dumping the clutch at the starting line. I'm not disagreeing with you, just giving real world #'s. It is still nothing like 1800 ft/bs through a 14.40:1 lo/lo, which is 25920 through the drive shaft.

Even so, they do make aluminum and carbon fiber drive shafts for trucks that handle that torque. But IMO, is it not cost effective and will not gain any measureable fuel useage reduction.