6.5 whoop whoop!

[Hammerhead]

This is old knowledge. In fact it was figured out before WWII.
Aerodynamic Drag. Aerodynamic drag increases linear with speed. (At least until you're exceeding several hundred mph. Close enough for the purposes of this discussion.)
However, the HP to overcome AD does NOT increase linear. In fact to double the speed of a vehicle, the HP requirement to overcome the effects of AD squares.

Example:
Funny Cars.
Take two equal bodied FC's, one Alcohol and the other Top Fuel and put them on the starting line of a drag strip with two equally competent drivers.
It doesn't matter the fuel composition, they weigh the same, they have the same tires for traction, they have the same w/b...blah blah blah, they're equal. Except for power!
Trip the Tree and watch the race for fun if you care.
Now let's look at the tale of the test. A drag strip has timing meters located at 60', 180'(optional), 330', 660'(along with speed recording) 1000', and of coarse at the 1320' finish line (also with the speed recording).
With two competent drivers and crew chiefs tuning the cars the 60' & 180' will be nearly identical. Why? Because at this stage of the track HP has very little influence, they both have way more than enough power to spin the tires.
Let throw out the 180' to 660' because it doesn't demonstrate anything for this discussion, for or against. Note at this point the TF car is starting to pull away from the A car because traction has been overcome and aerodynamic drag is starting to take its effect.
Now we're getting somewhere. Let's look at the two cars MPH from 660' to 1320'. The Elapsed Time does not pertain to this discussion.
The TF car will be about 10% faster than the A at 660'. That means the TF car is already fighting more AD than the A car. Remember EVERYTHING except power is EQUAL between the two.
The AD requires somewhere around 75-80HP to overcome at half track. The TF car is traveling approx 190mph to the A 170.
The TF car will be somewhere around 320mph at the finish line, or nearly double the speed...and squaring the HP requirements at 5625-6400. They produce about 7500hp.
The A car on the other hand will barely break 250mph, because they only produce about 2500hp and simply cannot overcome the AD to go much faster.

Now everybody looking at this straight on will say "Well yeah stupid, the TF car has more power so of coarse it can go faster."
Yes. It does and it can.
Now look at the other side of it. The cars are EQUAL in every aspect OTHER than HP. Add speed, and the ONLY thing that changes is Aerodynamic Drag.
When Rawze says speed costs money, this is exactly what he's talking about. Any truck, I don't care who's, what, or how. EVERYTHING on THAT truck is identical at 55 and 70...EXCEPT AERODYNAMIC DRAG AND THE POWER REQUIREMENTS TO OVERCOME IT!!!

Power=Fuel=$$$ Can't change it no matter how hard you try.