The combination of the boxy shape of the front end, relatively high angle of the front windscreen and the lack of a rear diffuser exposing the rear bumper to collecting underbody air flow culminate to a Cd around 0.34. Certain modern sports cars also have Cd's of around 0.34 but usually incorporate aerodynamic aids to increase downforce at the expense of some drag yet the S2000 has little to none of these and thus generates large amount of lift at higher speeds. It suffices to say that aerodynamics would be one area where the S2000 falls short when compared to the current models of sports cars.
Lowering any car will improve aerodynamics significantly and this would be done by my change of suspension to a high end coil over suspension yet the problem of overall lack of downforce would still need to be addressed with further modifications. I decided that a combination of a front lip or splitter and rear wing would be the first changes needed to be done to add downforce, hopefully without a huge increase in the Cd.
OEM options to increase downforce on the front of the car included the Honda Modulo lip and the Type S (or CR) front splitter but I ruled both of these out as I felt that a splitter extending out from the bumper would be a more effective way to generate downforce. This effectiveness comes from the pressure created on the top of the splitter to push the splitter down and air flow underneath the splitter which helps to suck the splitter down.
The APR carbon fiber splitter extending about 2.5 inches from the front of my bumper was my choice but decided against mounting the splitter on the bumper which is a typical fitment by most buyers. This is because I have had feedback from folks running on high speed tracks that the additional downforce created could be so high that it could cause huge pressure on the bolts holding the bumper on and in some cases even tear the bumper off. My decision was then to mount the splitter to the chassis with the construction of a splitter frame bolted to the splitter. This had a two fold benefit: 1. To create a frame strong enough to hold the splitter firm during high downforce situations 2. To create a linear increase in downforce transfer to the chassis. The result after fitment was noticeably large amounts of grip which increased with the higher speeds I drove.
The next on the list would be the hunt for a rear wing which my S2000, being a non-Type S version, did not come with from the factory. Various choices abound for the S2000 including even chassis mounted offerings but needing to balance the need for the boot (for carrying of my spare tyre to the track) with best available downforce ability, I chose a Voltex wing for my car. I selected Voltex Type 2 with a 1600mm wingspan over a Voltex Type 3 as my car would fall under the lower power category and the drag from the Type 3 might be excessive compared to the acceleration ability of my car.
To enhance the downforce capability of the Type 2 wing, I had it mounted the highest available mounting at 275mm to put the wing in the cleanest airflow above the profile of the car. Looking at wind tunnel tests on the S2000 showed me that the high windscreen of the S2000 does necessitate a high mounting for a rear wing to be effective. I also specified a gurney flap (or wickerbill) to be included to be fitted to the wing which would increase downforce without a large increase in drag. The result of the fitment of the wing was a significant improvement in high speed stability to a point that high speed corners that usually made the tail feel light and prone to oversteer now could be taken with more aggression with the large increase in grip delivered by the wing.
I did not feel a noticeable increase in drag at with the aerodynamic setup and a check of my fuel consumption showed little or no difference in my fuel consumption on day to day highway driving so I am pretty satisfied with the balance of grip and drag offered by this setup. Setting of the wing rake or Angle Of Attack would need more frequent track sessions for me to determine what would be optimum so I will need to wait until later this year to get a bit more feedback. The key point I have learnt with aerodynamic modifications is the need to balance the grip you add to the chassis as too much front or rear grip will result in a significant bias to the car's balance which could lead to a poor handling at speed.
The final part I added to my S2000 to enhance aerodynamics was a Mugen FRP hard top. The soft top of the car flapping in the wind combined with the ribbed profile of the soft top mechanism disrupts the airflow above the car and causes drag which a hard top would reduce. This would increase the Cd and may significantly reduce the effectiveness of a rear wing. The OEM hard top is slightly heavier with a bigger glass rear windscreen but is more expensive to purchase locally and probably slightly less aerodynamic in my view. Being given a good offer for the Mugen FRP hard top, I decided to bite the bullet on the high cost and go for it. To be honest, I am not able to discern the aerodynamic gain of the hard top as I have had some other modifications done at the same time but feedback from various owners who kept everything else the same while changing to a hard top reported improved gas mileage coming from the improvement in aerodynamics.
The final item I am toying with getting to further improve the rear aerodynamics would be the addition of the rear diffuser but as I do not want to run too far off the budget I've set for myself, I am still putting that move on hold for the moment. There is also a concern on streetability as the low ride height of the S2000 (especially since I am on a race derived coilover suspension) might result in damage to the parts after contact with humps. Companies such as Spoon, Downforce and J's Racing do have splitter setups for the S2000 costing slightly more than 1000 SGD.