Time Attack Terror: FXMD’s Record Setting Acura NSX


NSX Billy Johnson's office
 Billy’s office includes a carbon fiber dash and switch containing center console.  The console has dials for brake proportioning adjustment, and switches for the various pumps.  A Motec dash helps Billy monitor the situation and Sparco seats and belts are the office chair of choice.  The fire extinguisher shown is for minor stuff as it is really expensive to discharge the 10 lb halon system!  The whole package is wrapped by a strong but lightweight chrome moly cage.

Of course any time attack car is going to have extensive chassis work and the FXMD NSX is no exception. The aluminum unibody was stripped to a bare shell and fortified with an extensive chromoly roll cage.  The cages function is not only to protect the driver but to provide much needed stiffness to the aluminum unibody.  In the realm of chassis tuning you cannot make the chassis too stiff as it makes suspension tuning much easier and makes the suspension more responsive to bump input. 

 NSX Roll cage
 The cage has NASCAR bars to give an additional level of driver protection.  Below, the NOS, Beer, Oreo and RPG switches are obviously fake, we hope.

 FXMD carbon dash

nsx roll cage
 A tube is inserted into this stub to give a sturdy and convenient jacking point.
nsx rollcage
 The cars critical electronics are mounted on a carbon bulkhead on the passengers side of the cockpit.
nsx halon system
An on-board halon fire suppression system helps keep things safe.
NSX dash
 Although the interior has lots of carbon, its all functional and not eye candy.  This is a real race car, not a show queen from the floor of HIN.

The stock forged aluminum control arms are used, because their light weight and strength is hard to beat!  However the squishy compliant rubber bushings are replaced with FXMD’s spherical bearings.  The bearings reduce friction within the suspension pivots making it more responsive to bump input reducing tire shock.  The precision bearings also eliminate deflection that can cause inaccuracies in the alignment that ultimately reduce grip and create unpredictable handling characteristics.  The general suspension geometry of the NSX’s unequal length A-arms is pretty good so no pivot relocation or other geometry altering mods are done other than modifying the tie rods for fine tuning the bump steer.

NSX Sperical bearing control arms
 FXMD spherical lower control arm bearings take the slop out of the suspension with low friction.
sperical bearing NSX
 More spherical bearings on the toe links
Sperical bearing NSX FXMD
 FXMD spherical upper control arm bearings take the slop out of the suspension.
FXMD lower control arm
 Spherical bearing mounted forged aluminum lower control arm with brake ducts and bump steer adjustable tie rods shown here.
FXMD NSX tie rod
 Bump steer can be adjusted by shimming under the spherical bearing in the tie rod end.

Dali racing fully adjustable antisway bars help make the car easy to quickly adjust the balance of the chassis during a time attacks limited setup time.  The Dali bars are linked to the suspension via spherical end links and hard polyurethane bushings.  A Dali Racing compliance clamp eliminates an issue that all high G-load NSX’s experience. 

dali racing end link nsx
 The Dali Racing rear swaybar is adjustable here.
dali racing nsx swaybar
 The front Dali Racing sway bar is a tubular torsion type with adjustable arms.
dali racing nsx rear swaybar
 The rear bar in place with the rear diffuser off.

The NSX was designed with a unique design feature, a compliance link that allows the upper and lower control arm to move backwards under bump impact.  Unfortunately this link allows for unwanted changes to the toe, caster and even camber settings when stressed by tires that are bigger and stickier than what the engineers originally designed the part for.  The problem is made worse as the compliance bushings age and soften.  The clamp is a simple fix that solidly couples the rubber isolated compliance link with its shaft which is mounted solidly to the chassis, not allowing it to deflect under load.  Although this slightly degrades the ride, it greatly improves handling.

Dali racing NSX compliance link
 The Dali Racing compliance link eliminates an area where huge amounts of squish and flex can take place.

The most important part of any racing suspension system is the dampers.  KW supplied a set of their world-class 3-way motorsports dampers.  The KW dampers feature a mono tube construction with remote reservoirs.   The remote reservoirs allow for packaging a length sensitive mono tube in a shorter package with room for high and low speed compression damping adjusters and sufficient gas volume to prevent problems with gas reaction forces and to make canister gas pressure a useful tuning adjustment as well.

KW NSX shocks
 The sophisticated KW Motorsports 3-way adjustable monotube damper uses a main spring and a low rate helper spring.  The helper spring is not a progressive tender spring, its main job is to keep the main spring from being loose.

The KW’s also have low speed rebound damping adjustment.  The multitude of damping adjustments allows the shocks to perform a function of platform control vs simply attenuating spring rebound energy.  The most critical elements of damping control come at low suspension movement velocities where the shock shaft is moving at only 2 inches per second and below.  This is the range where most body motion that is detrimental to a cars handling occurs, like body roll, pitch and dive.  Damping at low shaft speeds is very difficult for most shocks as fluid flow is very low so metering is difficult.  This is no problem with KW’s sensitive precision valving. 

KW NSX shock remote resoviour
 The high and low speed compression damping adjustment is the gold and purple screws on the body of the remote reservoir shown here.  The low speed rebound adjustment is on top on the shock shaft.

An interesting property about KW’s motorsport dampers is their frequency sensitivity.  This allows firm control of body motion while still allowing supple response to high frequency bumps that can cause loss of traction.  The ability to give the dichotomy of firm control with a plush ride makes KW’s a big advantage and have really helped the NSX become a precise handling machine.

kw nsx shocks
 The gas reaction force of the KW damper can be adjusted with high pressure dry nitrogen through the shraider valve on the end of the remote reservoir.

Lightweight CCW C10 three-piece wheels, 18×10 front and 18×12 rear, hold either Yokohama A048R Compound DOT tires, 265/35-18 front and 315/30-18 rear or Racing slicks, 280/650-18 front 330/710-18 rear depending on what class and sanctioning body that car is being run in.  Redline Time Attack allows full slicks for its unlimited class.

 Custom offset CCW forged lightweight 3 piece wheels allow the biggest tire combo possible while maintaining proper offset and scrub radius.


Leave a Reply

Your email address will not be published. Required fields are marked *