If you've watched a Formula 1 race in the past decade or so, you've probably noticed some funny-looking fins below the cars' rear wings. These are called diffusers, and they're simple aerodynamic devices that create a low-pressure area under the car to increase traction. We'd seen them on our competitors' cars in B Modified, so we decided to try one for ourselves.
We began by measuring the available area under the car, as we wanted to fit the largest diffuser possible. The next step was to make a buck (or male mold) out of blue insulation foam. Based on our research, we settled on a few measurements: a diffuser angle of 12 degrees and 5 inches of rise for the 24-inch-long rear section.
Next, we layed up an outer shell for the diffuser. This would form the backbone of the piece and also function as our car's lower belly pan, taking the place of some aluminum sheet metal that was covering the underside of our engine bay. Once the shell was cured, we sanded it down and made strakes and stiffening ribs out of corrugated polypropylene sign material. These pieces were epoxied in place.
After the polypropylene cores were solidly planted, we wrapped them with carbon fiber—essentially making a very light and stiff sandwich. We let that cure, did some more detail sanding, and then finished off the piece with some carbon fiber wrapping around the back edges to make it look pretty.
All told, the piece weighs under 5 pounds. In theory it should help our car stick to the ground, even at autocross speeds.
