Wilwood Forged Narrow Superlite 6R Big Brake Kit Explained

By Core Brake Parts Tech Team — Circleville, OH warehouse

The Wilwood Forged Narrow Superlite 6R (FNSL6R) big brake kit pairs a forged six-piston, radial-mount caliper with a larger two-piece rotor on an aluminum hat. Wilwood engineers these kits for specific vehicles so they bolt on, work with the original master cylinder, and keep ABS working where the car has it. The catch: you need wheels large enough to clear the caliper, and you have to pick the version (street Hat kit or Race kit) that matches how you actually drive.

What the FNSL6R Caliper Is

Wilwood describes the FNSL6R as its newest version of the Superlite caliper series, adding radial mounting to a caliper family that was already widely used. "Forged" refers to the aluminum body, "Narrow" to its slim profile, and "6R" to six pistons and a radial mount. The radial mount uses a 5.98 inch mount spacing and bolts to an application-specific bracket, and shims let the installer center the caliper over the rotor.

The caliper uses differential bores: the pistons are not all the same size. Wilwood's install sheet tells you to mount each caliper so the largest pistons sit at the rotor exit end, in the direction the rotor turns. That is why the kits ship with distinct left and right calipers that cannot be swapped side to side.

Thermlock pistons are Wilwood's heat-management option for hard track use. For a street car, the stainless-piston caliper is the version most kits use.

Hat Kit vs Race Kit: Which Version Fits Your Driving

Wilwood sells the FNSL6R big brake as several kit families. The two you will see most often for late-model cars are the Hat kit and the Race kit, and they are built for different jobs.

The Race kit is not a better street kit. Wilwood warns that extended low temperature use of the race-spec pads causes premature rotor and pad wear. If the car is driven to work and taken to a few track days a year, the Hat kit with a street pad makes more sense. If it lives on a trailer, the Race kit is the tool.

Wilwood's install sheet for the 2012-and-later Scion FR-S / Subaru BRZ kit (base part 140-12870) shows what a typical bolt-on package contains: caliper mounting brackets and hardware, a 12.88 inch by 1.10 inch GT rotor on a big brake hat, a rotor registration adapter, the FNSL6R calipers, a set of BP-10 compound pads, and a stainless steel braided flexline hose kit.

Why a Bigger Rotor and Six Pistons Stop Better

A larger rotor puts the pads farther from the hub center, so the same clamping force produces more braking torque. More rotor mass and a vented design also absorb and shed more heat before the pads fade. Six pistons spread clamping force along a longer pad, which helps pads wear evenly instead of tapering.

What a big brake kit does not do is make a tire grip harder. On a street car in a single panic stop, the tire is usually the limit. The real payoff is repeated hard stops: mountain descents, autocross runs and track sessions, where stock brakes overheat and the pedal goes soft.

Heat also reaches the fluid. Federal Motor Vehicle Safety Standard 116 sets the minimum dry boiling point of DOT 3 fluid at 401 F and DOT 4 at 446 F, with wet (water-contaminated) minimums of 284 F and 311 F. Fluid that absorbs moisture boils sooner, and boiled fluid means a spongy pedal no matter how large the caliper is.

• Wilwood's install instructions call for its Hi-Temp 570 grade fluid or higher, and its EXP 600 Plus racing fluid for severe braking or sustained high heat.
• Old fluid must be completely flushed out, not just topped off.
• Wilwood states that silicone DOT 5 fluid is not recommended for racing or performance driving.

Wheel Clearance, Brake Lines and Master Cylinder

Wheels. Check this before you order. The kit pages list the minimum wheel diameter (17 inches for the Race kit, 18 inches for the 14 inch Hat kit), but diameter alone does not guarantee a fit. Spoke shape and barrel profile matter. The BRZ kit sheet includes a wheel clearance diagram and requires at least 0.080 inch of clearance between the wheel and caliper in all areas. Wilwood also notes the wheel track can change with an aftermarket brake, so check wheel offset before final assembly.

Brake hoses. Wilwood says OEM rubber hoses generally cannot be adapted to its calipers, which use a 1/8-27 NPT inlet. The kits use braided stainless flexlines, either included or ordered for the model. Route them so they cannot touch suspension, rotor or wheel through full steering lock and suspension travel. If you are replacing lines on the other axle at the same time, see our braided and OE-style brake lines and brake hoses.

Master cylinder. The kits are engineered to work with OE master cylinder output. Wilwood's pedal test after bleeding is that the pedal should be firm, not spongy, and stop at least 1 inch from the floor under heavy load. If the pedal still goes to the floor after repeated bleeding with no leaks, Wilwood says a master cylinder with a larger bore (more displacement) may be needed. If your original unit is leaking internally or worn, replacing it during the upgrade is cheap insurance; browse brake master cylinders.

How Hard Is the Install

This is a bolt-on job for someone experienced with disc brakes, and Wilwood states installation should only be done by such a person. Plan most of a day for the front axle, plus time to bleed and bed. The key steps from the Wilwood sheet:

1. Remove the OE caliper and rotor, clean the hub face and remove burrs so the hat sits flush. A hat that does not sit flush causes rotor runout.
2. Bolt the rotor to the hat with thread locker in a criss-cross pattern. Torque every fastener to the values printed in your kit's data sheet; they differ by kit. On the BRZ kit, for example, the rotor bolts are 155 in-lb, the bracket bolts 60 ft-lb and the caliper nuts 30 ft-lb.
3. Install the bracket and caliper, then look through the top of the caliper. The rotor must be centered; adjust with equal shims on both bracket bolts.
4. Fit the pads and check that the top of the pad is flush with the rotor's outer edge. Shim between caliper and bracket if it is not.
5. Mount the wheel with lugs torqued to spec and spin it to make sure nothing rubs.
6. Bleed starting at the caliper farthest from the master cylinder, outboard bleed screw first, then inboard.
7. Run Wilwood's minimum test: hold firm pedal pressure for several minutes, make hard stops at 2-5 mph while turning lock to lock, check for rubbing and leaks, then make moderate and hard stops at 15-20 mph.

Then bed the pads. Wilwood's procedure is a series of light on-off stops (3-5 seconds on, about twice that off), then medium to firm stops, then 8-10 hard stops from 55-65 mph down to 25 mph, followed by a cool-down drive. Do not sit with the pedal held down on hot brakes. The rotor faces should come out with an even burnished look; smearing or blotches mean the brakes were heated too quickly.

Pads, Rotors and Parts to Plan For

The FNSL6R uses the 7416 pad plate shape, so replacement pads are chosen by that plate and a compound. Wilwood lists BP-10 as a high performance street compound with medium friction, improved friction and lower dust than standard replacement pads, and a 500-1000 F working range. Drivers who run sustained track sessions typically move to a higher temperature race compound, accepting more noise, dust and cold wear.

Because the rotor ring bolts to the hat, a worn rotor can be replaced as a ring while the aluminum hat carries over. The rear brakes stay stock with a front-only kit, so make sure the rear pads and rotors are healthy before judging how the car stops. Shop brake pads and brake rotors for the rear axle, and brake calipers if a rear caliper is sticking.

Frequently Asked Questions

Will a Wilwood FNSL6R big brake kit work with my ABS?

Wilwood states the Hat kits are engineered for OE master cylinder compatibility and keep ABS function where the vehicle has it. The ABS unit and wheel speed sensors stay in place. Buy the kit listed for your exact make, model and year.

Do I need bigger wheels for this kit?

Yes, on most cars. The 14 inch Hat kit requires at least 18 inch wheels and the 12.88 inch Race kit at least 17 inch wheels. Even at the right diameter, check the kit's wheel clearance diagram, because spoke design can still hit the caliper.

Can I use my factory rubber brake hoses?

Generally no. Wilwood says OEM rubber hoses usually cannot be adapted to its calipers, so the kits use stainless braided flexlines made for the caliper inlet.

What is the difference between stainless and Thermlock pistons?

Thermlock is Wilwood's piston option for managing heat during hard, repeated braking. It comes standard in the Race kit. Street kits typically use stainless pistons.

Is the Race kit OK for a daily driver?

Not a good fit. Wilwood warns that its race-spec pads wear rotors and pads prematurely under extended low temperature use, which describes normal commuting. A Hat kit with a street compound is the better daily choice.

What brake fluid should I use after installing it?

Wilwood specifies its Hi-Temp 570 grade or higher, and EXP 600 Plus for severe heat. Flush all the old fluid out, and avoid silicone DOT 5 for performance driving.

Sources

1. Wilwood - FNSL6R Calipers - caliper description, piston areas, rotor widths, 14.00 in maximum rotor, 5.98 in radial mount, 7416 pad plate, finishes
2. Wilwood - Forged Narrow Superlite 6R Big Brake Front Kit (Hat) - 14.00 in rotor, 18 in minimum wheel, OE master cylinder and ABS compatibility, rotor and finish options, applications
3. Wilwood - Forged Narrow Superlite 6R Big Brake Front Kit (Race) - 12.88 in Spec37 GT rotors, 17 in minimum wheel, Thermlock pistons, race pads, low temperature wear warning, applications
4. Wilwood DS-947 - FR-S / BRZ Superlite 6R Front Kit Assembly Instructions - kit contents, 0.080 in wheel clearance, hose and inlet notes, torque examples, shimming, bleeding order, fluid, pedal and minimum test procedure
5. Wilwood - Brake Pad and Rotor Bedding Steps - bedding sequence, speeds, cool-down and post-bedding inspection
6. Wilwood - BP-10 Brake Pad Compound - BP-10 street compound description and 500-1000 F range
7. 49 CFR 571.116 (FMVSS 116) - Motor vehicle brake fluids - minimum dry and wet boiling points for DOT 3 and DOT 4 fluid