So I'm using said calculator:

http://www.rbracing-rsr.com/aerohpcalc.html

And am trying to figure out how much hp it would take a 350Z to hit 200 mph. Now judging by my horrible math skills, I'm getting ridiculous numbers for the frontal area. I'm getting a 3667.3775 or something like that.

To calculate the frontal area its (height x width) x .85. And to my calculations you need approx. 4500 hp or something wild like that. So I played with some more numbers and calculated a 350Z needs roughly 280 hp to hit 155 which sets the frontal area at about 37. Which to me roughly 6400 rpm in 5th is approx 280 hp at the crank in a stock 06.

Where am I wrong? Any more precise ways to calculate frontal area?

 

by thinking the Z can even hit 200 mph in the first place.

 

PLay forza, youll hit 200 fine.

On a serious note, the power isnt your main concern. Its staying your *** on the ground. Look up i think XKR's mach 1 thread where a couple of the big dogs discuss diffusers and such to keep them on the ground at near 200 mph speeds.