The first step in any product design process is to identify a market demand. As car enthusiasts and engineers, we are constantly striving to create new products and improve existing designs. You might ask why would you want to redesign an existing OEM Vortex Generator? The answer is simple. When OEM’s design a part/product the number one design consideration is producibility and cost. In a world where millions of vehicles must be produced in less than a year, parts must be able to be manufactured in a matter of seconds to meet production demands. This creates significant limitations on what an OEM to produce, which often results in sacrificing performance to improve manufacturability.

We at Renegade Motorsports saw a great opportunity to improve upon the OEM and similar aftermarket ABS plastic Vortex Generators currently on the market. Or primary design goals were to provide improved aerodynamics and to manufacture the product out of high quality composite materials. Once the demand is identified and the design goals are known the next step in the process is to define the product geometry. To shorten our design cycle and ensure our products have perfect fitment, we 3D scanned the rear roof section of the car to produce an accurate 3D model.

Once we had an accurate model of the roof geometry, we set about designing the vortex generator itself. One of the main gripes that we have heard about the OEM part is that it does not extend all the way to the roof seam edge. Utilizing the scan data, we were able to ensure that our part matches the lines of the roof exactly. We were also able to improve the fitment around the rear antenna by reducing the clearance relative to the OEM part. With the fitment issues solved, the next step was to create a fin shape that would optimize vortex generation.

Every design consideration in aerodynamics is a tradeoff between two competing goals. The challenge of this design was to reduce the flow separation drag on the rear window by injecting turbulent vortex energy into the flow. The problem is that fins protruding into the flow create their own drag, so a well-designed vortex generator trades a small fin drag increase for a much greater decrease in overall drag. After an exhaustive period of research and analysis we arrived at a wishbone fin design to best solve these challenges. Stay tuned for an in-depth article on vortex generator aerodynamics.

Once the fin design was finalized, we moved into the detailed design phase and created a 3D CAD (Computer Aided Design) model that would be used to create a mold plug.

A CNC program was then written, and a positive mold plug was machined out of MDF (Medium Density Fiberboard).

In order to make a mold from the MDF plug, Surfacing primer was sprayed on top of the sealed MDF plug and meticulously sanded and polished to a mirror finish. Although extremely labor intensive this is the most important step in the entire process. Any surface defects or scratches left in the plug surface will transfer to the mold and ultimately the finished product. Once we were satisfied with the high-quality plug surface, a high temperature epoxy surface coat was applied to begin the construction of the mold.

To support the surface coat, layers of fiberglass and high temperature epoxy were laminated on top of the coated plug. This process continued until we built up enough laminate thickness to achieve the desired mold stiffness. After allowing the laminated mold to fully cure, it was released from the plug to form a negative cavity in which to produce parts.

We currently utilize two methods to produce composite components. The first is out of autoclave pre-preg or “Dry” Carbon Fiber molding, which is used for our carbon fiber parts. The second method, which we will discuss in this article is vacuum resin infusion. We use the resin infusion process on our fiberglass color matched products, because it yields a stronger and lighter part than traditional wet layup methods can produce. You might ask, why do you make fiberglass parts, Isn’t that a cheap alternative to carbon fiber? Every product that Renegade Motorsports produces is optimized for its application. Given that this component is non-structural and is painted to match OEM paint codes, we decided that we could offer more value to our customers by manufacturing the product out of fiberglass.

The first step in the manufacturing process is to spray the mold with an automotive grade surfacing coat. After the surface layer is sprayed, the dry fiberglass templates are loaded into the mold and pressed tightly against the mold surface to avoid entrapping any air bubbles. Plastic release film and resin infusion media are then added which allows for uniform resin flow through the part. Once all of the materials are in place, the mold is sealed and placed under a vacuum to provide compaction of the fibers.

Although a vacuum might not seem like a lot of force, consider that sea level atmospheric pressure is roughly 14.7 pounds per square inch. If we remove all of the air in the vacuum bag and are able to drop the pressure to 0 psi, that means 14.7 pounds are pressing on the part for every square inch of surface area. Given that our vortex generator is roughly 264 square inches, this means that almost 4000 pounds of force is compacting the fibers under full vacuum. This results in an extremely strong and lightweight part, since the amount of resin used is minimized by the compacted fiber volume. Once full vacuum is achieved and we are certain there are no leaks in the bag, a resin feed line is opened and vacuum pressure forces the resin into the fibers. After resin has flowed through the entire part, the resin line is clamped, and the part is allowed to cure under vacuum.

After a full cure has been achieved the part is de molded and moved to finishing. Currently we offer all of the Subaru OEM factory paint colors, but we can also do custom colors upon request. We hope that you have enjoyed this post and found the information within interesting and informative. As always, Renegade Motorsports appreciates customer feedback and we strive to foster a community of like minded enthusiasts.

As such, we will offer a 10% discount to anyone who shares our content on social media and tags Renegade Motorsports. All you need to do is tag us and send a screenshot to and we will respond with a coupon code. Thank you for reading and stay tuned for future posts on vortex generator aerodynamics and carbon fiber materials.