We did a lot of developing the front splitter on the Cayman GT4 so we thought it would be nice to share our findings and expose a little glimpse at the depth of development for this product. First, we wanted to create a quality product capable of producing real results while costs down as much as possible. Here were our main goals:
1. Create real downforce up front
2. Accurate fitment
3. Cost, durability and strength
There are actually quite a few solutions out there for creating downforce in the rear of the car. We have wing risers, gurney flaps, diffusers, and larger wings. It is easy to create a lot of downforce in the rear but the front of the car tends to be neglected. Without balanced aerodynamics on a car, a driver will easily find themselves fighting with excessive understeer. Even though the car maybe faster, it's just not that fun to drive and even odd tire wear issues may start to show. There are really only 2 main modifications for front downforce on the market right now. Canards and splitters. Canards are great for balancing but don't produce that much downforce in the front. They often come with high drag penalties and can only do so much and will not balance out a larger wing. With that said, this is why we spent a lot of effort into developing this.
Of course like all our aero products we used some CFD to aid in the design. The front was tested out with 2 main designs. The first design was to simply lower the front of the bumper closer to the ground. Adding a lip that extends vertically from the front of the bumper and towards the ground by 1" increases the downforce by about 20lbs~ (@80mph) according to our findings. This air dam is surprisingly super effective and can cheaply be done. However, a lip that extends downwards to the ground is obviously exposed to more elements and can be damaged easily. There is also a limit to how far you can extend it down before this becomes impractical. Thus, in order to balance out a wing in the rear that can generate 150-200lbs of downforce @80mph (what we are shooting for with our rear wing), we needed to look into another design.
The second design we looked into and obviously chose, is a splitter. Splitters stick out from the original bumper and create a platform or area for which high pressure air can push down on the car. The bottom side of the splitter provides smooth free flowing air which lowers the pressure under the splitter. Since air goes from high pressure to lower pressure, an effective force is produced between the two "split" regions. This is where the name splitter comes from. As you can see in this picture below, the red zone is high pressure low velocity air, and the blue zone underneath the splitter is blue. Blue is low pressure high velocity air. The further out it sticks out, the more surface area there is to create more downforce but the longer the overhang on the car. This makes it easy to scrape on the ground during bumps and changes in elevation. After much track driving and road cruising (we went through some bumpy, hilly San Francisco streets), we settled on an aggressive ~4" extension from the front.
One feature you may have noticed on the bottomside of our splitter is the front pair of diffusers. These scoops, channel air from under the diffuser and into the wheel well. They create a suction effect to help increase the speed of the air under the splitter even more. Look cool but do they actually work?
Well, we ran a CFD study with the flat spiltter without these scoops and compared it to one with the scoops added. Our flat splitter alone creates ~70lbs of downforce @80mph. With the diffusers, the front splitter sees a total of ~100lbs of downforce @ 80mph. That's a huge diffference(+43%)! This amounts to ~225lbs of downforce in the front of the car @120mph! That ought to put a dent in the aero car balance of this car.
Fitment & Accuracy
We started our design with a 3D scan of the front of the car. This allowed us to quickly find mounting points and studs for all the brackets that were required to support the splitter. We are able to get really accurate 3D positions allowing us to create mounts that will anchor the splitter directly to the chassis. You will notice in all our designs that a tolerance has been built into the design with slots. These allow for a little bit of adjustment but most importantly a good fit with all the variances from car to car.
Cost, Durability & Strength
One of the biggest contributors to cost is the material selection. This makes a huge difference to the overall cost of a produce and how it behaves under use. Our main choices were birch wood, alumalite, tegris, and carbon fiber.
Birch wood is a very common DIY material of choice for splitters on track cars. It's really cheap, durable, light, and stiff. Although a birch splitter can be made just as light as carbon fiber, it requires a thickness of about 11.5mm. This isn't too bad but it does make the splitter look thick and reduces some ground clearance. We actually made a single splitter in birch to test out fitment and function before the carbon fiber versions were ready. One of the largest downsides to birch is the look. We can paint it black but when it scrapes, the raw wood will be exposed. We also guess that not many people would want wood on their Porsche.
Alumalite is also another very common DIY material of choice for splitters. It's about 3-4 times as expensive as birch. It consists of a corrugated plastic core with thin sheets of aluminum on the outer surfaces. The exposed surface can be painted in black. This combination makes it light weight while maintaining stiffness. Aluminum does bend when it takes impact and can't be considered as robust as the birch. It requires a thickness of about 10mm for our loads but the main problem is that it is a little bit hard to source.
Tegris is about 5 times as expensive as Alumalite. This crazy thermoplastic composite material was designed for lightweight, stiffness, impact resistance, and lower cost. For our application Tegris would require a sheet thickness of about 11.5mm or just as thick as the birch. Since Tegris is a thermoplastic, it means we can make high volume parts through thermal molding. It's cheaper than carbon fiber manufacturing methods which are more labor intensive. Unfortunately for our splitter, we are not creating a molded part so cost doesn't seem to be a huge savings in this department unless we look at higher volumes. We see this material used for splitters on nascars but sourcing is extremely difficult as there is just one provider for this material.
Finally we have carbon fiber. Carbon fiber is extremely light yet stiff which is great for front splitters. Also a lot of carbon fiber pre-made into flat sheets can be found. This makes it decently economical for making a front splitter. For our applications only 3mm thickness is required too which gives us more ground clearance. One of the biggest questions about this material though, is its durability during impact. Because carbon fiber is such a stiff material, it tends to crack on impact rather than flexing away. However, in reality we found that 3mm thick sheets do have some limited flex to them allowing the splitter to be decent even when hitting some light berms. Who doesn't like carbon fiber! It looks great and is light but the cost has always been scary. After doing much research we discovered that the pricing is actually cheaper than what we can source Tegris at.
So there you have it. We made a solid, chassis mounted, carbon fiber front splitter, designed by Jacob. Yes.. this is not just for show boys and girls. It easily supports a 165lb guy on it and yes, it does produce quite a bit of downforce at high speeds!
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