OK, I know I must have too much time on my hands - actually I'm in full-blown avoidance of real work and responsibility - but my loss is your gain. Here's some fun facts about our Crossfires.

If you dropped your Crossfire from an altitude of greater than 3900 feet, and assuming the nose stayed pointed downward, it would reach a terminal velocity of 408mph at sea level. That's a fast Crossfire!

Drag - or air resistance - saps horsepower from making your car go faster, and uses it to force the air out of the way. So how fast - theoretically - could your Crossfire go? That depends on which XF you have, and if you've modded it or not.

Use this equation to figure out how much drag your car has at different speeds:

D = 0.002684 * Cf * Af * S^2

^2 indicates squared

Where D is the amount of drag in pounds of force. Cf is the Coefficient of Drag of the car. Af is the frontal area of the car in sq. ft. And S is the speed in miles per hour.

Hard-topped Crossfires have a Cf = 0.370 and Af = 20.56.
Convertible Crossfires have a Cf = 0.384 and Af = 20.62.

So when a hard-topped Crossfire cruises at 65 mph, the air around it is pulling backwards on the car with 86 pounds of force. Convertible @ 65 = 90 lbs.

That doesn't sound like much util you realize that air is in effect draining power from your ride. You can calulate power in horsepower. So how much is it loosing to the air? Hard-top @ 65: 15 whp, Convertible @ 65: 15.5 whp.

You can calculate the whp required to fight drag with this equation:

Pl = (0.05904 * Cf * Af * S^3) / 8250

^3 indicates cubed.

Where Pl is the whp required at a speed of S mph.

Here's a quick table:
_____________Hard-Top____________Convertible____
Speed_____Drag_____HP_Loss_____Drag_____HP_Loss
=========================================
10_________2.04______0.05________2.13______0.06
25________12.76______0.85_______13.28______0.89
55________61.76______9.06_______64.29______9.43

65________86.26_____14.95_______89.79_____15.56
75_______114.85_____22.97______119.54_____23.91
85_______147.52_____33.43______153.55_____34.80

100______204.18_____54.44______212.52_____56.66
125______319.03____106.33______332.06____110.67
150______459.40____183.73______478.17____191.24

160______522.69____222.99______544.05____232.10
170______590.07____267.46______614.19____278.39
180______661.53____317.49______688.57____330.47

190______737.08____373.40______767.20____388.66
200______816.71____435.52______850.09____453.32

As you can see, the horsepower requirements for keeping your car going increase dramatically as the speed goes up. Using stock whp measurements of the base model (~175) and SRT (~290), you can see that a Crossfire's top speed is physically limited by aerodynamics.

Speed limitations due to drag:
Base Hard Top: 147.6 mph
Base Convertible: 144.6 mph
SRT Hard Top: 174.7 mph
SRT Convertible: 172.3 mph

Now, if you really want to talk about fast, and join the 200+ mph club, you would need to be getting more than 435 horsepower at the wheels just to overcome drag at that speed. That's about 50% more power than a stock SRT has. I don't think anyone will be joining the 200+ mph club in a Crossfire any time soon.

Keep in mind that the above numbers do NOT account for the rolling resistance of your tires. So the theoretical top speeds of our cars would be even less than listed above.