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The underbody of the Ford GT is just about a flat bottom.
The flat bottom leads to this working race car like rear diffuser. This makes a lot of downforce and is surely critical to the car staying on the ground at 280 mph. 
The rear diffuser has a kickup whose angle is pretty extreme and it would seem that you might get flow detachment and stalling. However, Ford added a lot of vertical strakes which work like vortex generators to allow the flow to stay attached to the roof of the diffuser. This diffuser was designed using CFD and wind tunnel data so it does work!
The nose mounted radiator has the air exit in the hood of the car. This contributes to front downforce as well.
The huge 3.5″ exhausts on either side of the drag chute are made from 321 stainless by M2K Motorsports. The smaller pipes exiting lower on the car are discharge pipes for the big Precision Turbo 66mm wastegates. 
The M2K Motorsports crew works late into the night at the Texas Mile getting the car ready to make its record smashing pass. The fact that besides the engine, the Ford GT is mostly stock and working well speaks a lot about the engineering behind the base car. 
