Using some leftover ABS plastic sheet from my Cruze Aerodynamic Engineering project, I decided to fabricate an underbody shield for my Focus SVT! As seen in the top picture to the left, the stock underbody has no shielding underneath, which has three negative consequences:

1.  Increases aerodynamic drag

2. Allows lots of corrosive salt-slush-snow-rain mixture into the engine bay during the winter months.

3. Increases air pressure behind the radiator, which lowers cooling system performance

Corrosion of engine bay parts - not something typically of concern - is crucial for older cars to keep them in repairable condition. The smaller fasteners and hardware in the engine bay, if corroded, are much more likely to snap when removing them.

I used a manometer to measure pressure difference between the front and back of the radiator package, which tells me how effectively air can move through my cooling radiator. I saw a modest, but noticeable 15% increase in the pressure delta. If my car is now 15% better at cooling the engine, I can block 15% of the front grill area and still retain my OEM cooling potential.

Blocked Grill Area = Less Aerodynamic Drag = Faster, More Efficient SVT Focus!