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Aerodynamically, the front of the car must be designed to get air moving over and under the car as smoothly as possible with minimal turbulence. In its attempt to give the S197 a retro look reminiscent of late-60's Mustang fastbacks, Ford provided the best possible balance between looks, functionality and ease of manufacturing to match the vehicle's performance and design goals. However, with its blunt front end, the drag coefficient is a dismal 0.38 by modern standards leaving plenty of room for improvement. Ford went some way to rectify the flawed design for the 2010 model year and, in doing so, reduced the drag coefficient by 7% to a more respectable 0.355. My aim was to replicate some of the modifications carried out by Ford.

Stock Engine Undertray

The 2005-2009 Mustang has a front undertray (Ford part no. 5R3Z-17626-BA) that's only slightly wider than the radiator and extends from the lower radiator support to the center portion of the front bumper cover. This leaves two large gaps between the side edges of the undertray and the left and right edges of the bumper cover. When the car is moving, air can become trapped in these pockets and create lift.
One solution is to swap in the wider front undertray from a 2010 Mustang (Ford part no. AR3Z-17626A) but that requires some trimming to fit properly and still leaves a small gap behind the center portion of the bumper cover. A cheaper alternative is to retain the 2005-2009 undertray but add extensions to each side to fill the gaps. I began by creating a cardboard template and then cut the required pieces from a scrap plastic fender liner. The pieces were attached to the existing undertray with self-tapping screws and the modified undertray was a perfect fit.

Modified Undertray with 2010 Heatshield

The next step was to retrofit the louvred heatshield from a 2010 Mustang (Ford part no. AR3Z-6C038A) to fill in the gap between the lower radiator support and the K-member. The heatshield fits directly without any modification using the supplied inserts/fixing screws, and can easily be removed when it's time to change the engine oil filter.
The photo on the right shows how the undertray and heatshield are positioned in relation to each other. The heatshield smoothens the flow path of air passing under the engine, while the louvres create an area of negative pressure that draws out hot air from behind the radiator to improve engine cooling at highway speeds. Hood flutter, common on 2005-2009 Mustangs at highway speeds, is reduced by preventing additional air from becoming trapped in the engine compartment. Highway fuel economy is also improved due to reduced drag.

Radiator Extension Covers

These CDC radiator extension covers aren't an aerodynamic upgrade but they do clean up the look at the front of the engine bay. Makes you wonder why Ford didn't fit them from the factory in the first place.
Note that I also installed a pair of Redline Tuning hood struts. Another item that Ford could have fitted in the first place!