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Honda S2000 Diffuser - Diffuse This - Wrenchin'

Password:JDM S2000 Undertray:What It Does. How To Install It.

Phi Phung
Sep 1, 2008
Photographer: Courtesy Of Password:JDM
Htup_0809_01_z+honda_s2000_diffuser+undertray Photo 1/17   |   Honda S2000 Diffuser - Diffuse This - Wrenchin'

S2000 Aero Tricks
Aerodynamics is important, especially for those of us who want to go fast. It's also one of those tuning realms few actually understand. This crucial balance between drag and downforce is continuously scrutinized from major racing teams utilizing Formula 1 open-wheel chassis all the way to sport compact drag beasts. It doesn't really matter what you're racing, aero tricks will either help you or kick you in the ass. Many of the concepts that help propel an F1 car around and keep it on the track are implemented on mass-produced sports cars, you just might not realize it. Some manufacturers incorporate front splitters and rear wings into a vehicle's design in hopes of generating downforce. However, for those of us who can't afford to drive something with Italian horses or bulls badged onto the front grilles, more than likely, there's plenty of room for improvement with what we've got.

Htup_0809_03_z+honda_s2000_diffuser+rear_frame_braces Photo 2/17   |   The kit includes one of Password's rear frame braces. The brace stiffens up the subframe but also serves as a mounting point for the undertray.

Aero: Let It Help You
A good example is the S2000. It's light, nimble, and there are tons of lip and wing options offered that can help improve downforce, but aerodynamics isn't based solely on the air pressure moving along the top of the car-downforce-half the battle is fought from underneath. Some companies have developed rear diffuser options for the S2000 but Password:JDM owner, Steve Naing, is one of the few who's realized that there really wasn't a complete front-to-rear solution yet, so he made his own. Working with his team, Steve developed the first production undertray specifically for Honda's roadster. Installing one is easy. Knowing why you should pay for one is a bit more complicated.

Htup_0809_08_z+honda_s2000_diffuser+laser_cut_bracket Photo 3/17   |   A series of laser-cut brackets are bolted to the chassis and feature mounting points for the carbon pieces. Installation is simple and nothing needs to be removed. Simply loosen the rear antiroll bar mounts and slide the brackets in-between.

So what's the big deal? As long as you have a rear diffuser and a GT wing the S2000 should handle just fine, right? Well, sure, it's better than nothing, but it's far from complete. Understand that air moves across a car from all sides but, for simplicity's sake, we'll just focus on the top and the underside. The front splitter helps guide the air toward one of these paths. The air flowing across the top moves at a higher rate of speed and at a lower pressure when compared to the air flowing underneath. One of the undertray's obvious benefits is that it diverts air that could potentially cause drag away from the chassis. The less obvious benefit is that it guides high-pressure air out from underneath the car, through the back. This stops the high-pressure air from dwelling underneath, in turn, allowing for the downforce created by the rear wing and front lip to be far more effective. The difficult part is manufacturing something that's flat enough to channel all of this air out. The system requires panels that extend from the car's front to its rear, which is what Password:JDM did. The Password:JDM S2000 undertray is something of a masterpiece and, although Ferrari owners would never admit as much, it's enough to make even some of them green with envy.

Htup_0809_04_z+honda_s2000_diffuser+laser_cut_brackets Photo 4/17   |   Honda S2000 Diffuser - Diffuse This - Wrenchin'

The Solution And Why It's A Good OneRight about now you might be assuming that the Password:JDM undertray is just another JDM knockoff. If you are, then you're wrong. Password:JDM's system is an original design-besides, we just told you there's yet to be a complete front-to-rear S2000 undertray solution, so pay attention. A simple, single undertray could have been developed, but instead key factors were stressed during the design process-we know since we grilled Steve with as many questions as we could. The first key factor: It has to be a direct bolt in. A combination of water jet CNC brackets and threaded inserts are part of what makes this a reality. Of course, all of the hardware necessary is included, which makes mid-install hardware store runs a thing of the past. Even the washers are Password:JDM special issue; you know, those neat-looking, anodized fender washers you want to cover your engine bay with. The kit is even designed around the stock exhaust system and will fit with most any aftermarket one around.

Htup_0809_10_z+honda_s2000_diffuser+fender_washers Photo 11/17   |   Password:JDM fender washers everywhere. The breakaway rubber inserts are behind the carbon fiber.

Password:JDM was also concerned with material. It had to be rigid but light. Aluminum is rigid but since the area underneath is so large such an aluminum panel would need to be fairly thick in order to stay true. Not an option. Fiberglass is lighter but lacks the strength needed in case of impact. Steve opted for carbon fiber since it offers the best of both worlds, but such characteristics come at a price. Password:JDM just so happens to own its own carbon-fiber factory, which is fortunate for anyone interested in this undertray kit since all of this helps keep costs down. Nobody's saying the kit is cheap but, all things considered, it's a fair price for the amount of carbon fiber you'll end up toting around. Of course, the $3,400 price isn't the only thing that makes the kit so attractive. Password:JDM added a bead that spans the length of the undertray that helps minimize flex, and mounting points are strategically placed to help reduce vibrations. Heat shielding is also embedded in the carbon along the area running past the exhaust to ensure that heat's never an issue.

Htup_0809_12_z+honda_s2000_diffuser+shaving_fender_washer Photo 12/17   |   You'll need to shave one side of this fender washer to allow it to sit flat against the center panel's ridge.

Of course, performance was the most important factor. If Password:JDM's undertray can't perform better than what little S2000 underbody aero is currently on the market, then what the heck would all of this be for anyway? To make it happen, Steve and his crew simply had to channel the laws of physics to their advantage. Flatness is important here. From the front bumper to the gas tank, the entire underside is virtually covered. The rear diffuser angle was carefully calculated for both proper air speed ramping as well as fitment. Each fin is thinly constructed, yet solid enough to minimize air turbulence exiting the rear. Vents are also integrated into the undertray in order to release pressure and guide cool air in for keeping drivetrain temperatures in check. To be sure though, if the S2000's transmission or differential really got that hot, Honda would've likely integrated a cooling system for each. Channeling air through should suffice.

Htup_0809_15_z+honda_s2000_diffuser+tightening_allen_bolts Photo 13/17   |   With the Allen bolts tightened the undertray assembly isn't going anywhere.

Do-it-yourself. Now.
Installation is as you'd expect. The aluminum brackets must be installed first, then the rubber nut inserts are pushed into the body's undercarriage. Yes, the inserts are rubber, which gives the undertray a slight amount of play and, in the event of a collision, it allows the undertray to tear off the chassis instead of dangerously hanging up on something like a pothole or rut. Once the mounting holes are in place, the panels can be installed starting from the rear, moving toward the front. The front plate is secured to the front bumper. This allows just about any front lip or splitter to fit that you could possibly want and reduces the chance of damage that can be inflicted to the undertray in the event of a minor accident.

Htup_0809_13_z+honda_s2000_diffuser+transmission_jack Photo 14/17   |   A transmission jack makes the install a bit easier but, then again, so would a couple of friends.

Harnessing aerodynamics is critical to keeping a car under control. If you're not doing it, you're not getting all that you can out of your beast. Password:JDM's S2000 under belly diffuser is about as close to a real performance-bred racing concept as you're going to get. If you're looking for that last 10 percent, you know who to call.


Pico Rivera, CA 90660
By Phi Phung
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