Time Attack Terror: FXMD’s Record Setting Acura NSX


Performance Friction NSX brakes
 The massive 355mm Performance Friction brake upgrade on the FXMD NSX is the largest most powerful braking system for the NSX on the market.  Amazingly, this race proven set up is totally streetable and fully compatible with the stock master cylinder and hydraulic system.  No dual master cylinders needed here.  The NSX is capable of decelerating at an amazing 1.6+ G’s all day long with no fade or change in pedal effort.

 In a Time Attack car, the brake system is perhaps just as critical as the engine.  A successful car has to slow down rapidly and repeatedly from high speeds. FXMD NSX incorporates some innovative solutions for its braking requirements. Performance Friction was tapped on the shoulders to develop the ultimate brake system for the NSX.  So impressed by the brakes system are we that we will devote a lot of space to describe this innovative system. The cool thing about the system was that it was designed from the start to be fully compatible with street going NSX’s so anyone can have the same braking performance if they just contact FXMD.  Although Performance Friction is well known as the manufacturer of perhaps the best performance brake pads on the market, they are also well known in the world of elite racing as a supplier of extremely high quality brake systems.  Many Nascar and ALMS cars run Performance Friction’s parts with a great deal of success.  Now Performance Friction will be applying this knowledge to a line of ultra high performance street compatible brake systems.

Performance friction NSX brake system
The Performance Friction caliper is a true monoblock, machined from a solid forged blank.  Performance Friction’s engineers use FEA to optimize the shape for maximum stiffness and minimal weight.

Most racing brake systems are pretty elaborate needing a dual master cylinder system that uses a balance bar, pedal assembly and an adjustable proportioning valve.  These parts are necessary because racing brake calipers are usually only available with 2-3 different piston sizes and the hydraulic proportioning of braking force must be highly adjustable to accommodate this.  These parts are very expensive adding thousands of dollars to the price of a brake system and require elaborate custom fabrication to provide rigid mounting points in a car. Simply bolting a racing brake set up to a street car’s hydraulic system usually results in a bad brake bias.  This is one of the reasons why many aftermarket big brake kits have a longer than stock stopping distance. For street cars you can forget 100% compatibility with ABS, EBFD, traction and stability control systems as well.

Performance Frction 4 pad caliper big brake kit for NSX
 Any NSX owner can buy the exact same braking system that Billy’s NSX uses and expect the same level of performance.  You can see Performance Frictions innovative 4 pad per caliper system in this picture.

Performance Friction set out to cure this issue by designing the brake system around the NSX’s requirements.  The stock NSX hydraulic proportioning was examined as was the geometric mechanical advantage of the calipers due to caliper mounting geometry and rotor size to determine what the overall brake bias balance would be in static and dynamic simulation.  The piston sizing of the Performance Fiction calipers was configured to optimize the brake bias for the stock hydraulic system and rotor sizing.  Amazingly the FXMD NSX runs the stock brake hydraulic system with its Performance Friction brakes!

Performance Friction Caliper piston cap
 In this picture you can see more of Performance Frictions innovation.  The large cap showing in the lower caliper protects the piston from dust, helps isolate the piston from heat and gives a larger surface area to spread the brake force on the brake pad backing plate.  You can see the pistons without the cap on the upper caliper.

The Performance Friction calipers are shape optimized though Finite Element Analysis or FEA, enabling the best combination of light weight and the all important for pedal feel, stiffness.  Careful design also enables the calipers to have the lowest possible profile both radially and axially for wheel clearance flexibility.  The calipers have some very interesting design innovations that provide an unheard of level of performance for not just their race kits but their street kits as well.  The most interesting feature is the use of 4 small brake pads per caliper, one for each piston.  This prevents taper wear of the pads. The small, independent pads and pistons assure nearly equal hydraulic and braking force distribution, not only on the brake pads but throughout the caliper body as well.  This enables the caliper body to be pared down without sacrificing stiffness. The 4 smaller pads also have 4 leading edges, important because the leading edge of any pad produces the greater part of braking force due to the tipping moment created as the brakes are applied.  This gives greater bite than conventional calipers and pads.

FXMD NSX brake duct
The brake system is cooled by high pressure air diverted from the ducting leading to the intercooler heat exchanger in the front of the car.

The pistons are unique as they are buried deep within the calipers body, isolated from heat and protected from debris.  A large diameter cap covers the piston and provides a large surface area for the pad to bear upon to better distribute the braking force.  A heat resisting shield separates the piston cap form the actual piston and greatly reduces heat transfer to the brake fluid.  On the street versions of the caliper, a full bellows type dust boot prevent contaminants from coming near the seals.  For racing use the bellows are omitted which is standard practice for all racing calipers as it would be destroyed by racing levels of heat. The seals geometry is designed to optimize piston retraction to assure cool, drag free operation. The calipers forged body has stainless steel abutments for the brake pads to ride in to assure smooth application, low wear and positive pad retraction without bind.  Their abutments are aligned with the direction of brake force induced torque to reduce overall stress and flex within the caliper and mounting system.

FXMD NSX Brake duct
The duct blows cool air on the center of the rotor where it is drawn through the rotors vanes.

The 355 mm iron rotors are ventilated with the vent locations and geometry determined by extensive airflow, stress and thermal analysis.  The rotor axial and radial runout is closely controlled to a few ten thousands of an inch to assure nearly perfect balance.  The rotors are fully floated to reduce stress on the hats and the rotors themselves when hot.  Floating the rotors reduces caliper piston knock back under spindle flex.  A unique and innovative feature of the rotors is that the rotor to hat interface uses a lug system that takes the shear load off of the hat bolts and increases the bearing area so that the rotor float is freer from bind under brake torque load.  The rotors are also dimpled instead of cross drilled.  This gives the firebrand venting of a drilled rotor without the stress cracking that drilled rotors are plagued by.

Performance friction rotor lug floating drive and dimpled rotor
 A rotor is not just a rotor!  Performance Frictions rotor assembly bristles with innovative features.  The crack eliminating dimpled venting is obvious, less obvious is the fully machined inner and outer surfaces assuring near zero runout and perfect balance.  The full floating system uses lugs on the alloy hat and rotor to transfer braking torque to the hub.  This takes all shear load off the hardware.  The rotor is free to float on the lugs and held in place by the mounting ring and allen bolts.

Billy reports that the Performance Friction brake system is significantly better than any of the brake systems he has run previously on the car, including those made by major brand name brake companies even with the stock single master cylinder brake hydraulic system!



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