Forging Ahead: Swapping Wilwood’s Forged Superlite Radial Mount Calipers on a C5 Corvette Z06
Excepted from the winter 2021 issue of Chevy Hub Magazine
Words by Wes Duenkel
Photos by Wilwood Engineering
Wilwood has been an innovator in braking since 1977 and, throughout the years, continually improved the performance of its products. The Superlite caliper is a perfect example, having been one of Bill Wood's original designs for stock car racing.
For over a decade, Henry De Los Santos' 2004 Chevy Corvette Z06 used a Wilwood Superlite six/four piston brake kit for track days and autocross. They still work great, but Wilwood invited Chevy Hub to upgrade the current Billet Narrow Superlite (BNSL6) calipers to the latest Forged Narrow Superlite Radial Mount (FNSL6R) units.
The evolution of Wilwood's Superlite calipers is centered on increasing rigidity without increasing size or mass. The reason is simple: Designing everything to minimize deflection when the brakes are applied transmits more pedal force to clamp the pads to the rotors, with less effort wasted in flexing other components. The new design also incorporates an internal fluid crossover that allows the caliper end bridge to be stiffer and is less susceptible to damage than external fluid tubes, as used on the previous generation caliper.
The improvements start with the raw material; the latest Superlite calipers use a forged aluminum body instead of a billet. A billet's grain structure is one-directional, flowing parallel to the pistons because of the way the caliper blanks were extruded. The new caliper uses a stress-flow forged aluminum blank that aligns the grain structure with the shape of the caliper to increase rigidity. The result is a stiffer caliper that takes up less room, increasing wheel clearance over the previous generation billet caliper.
The Wilwood engineers utilized finite element analysis (FEA) to find where more metal would help stiffness and removed material in the design where it just added mass. The result is a caliper that weighs under five pounds - noticeably less than the old version.
Rigidity improvements carry over internally to the pistons themselves (six in the front and four in the rear in the case of this Z06). The stamped stainless steel cups used in the previous generation are superseded by stiffer machined investment cast stainless, with a shape optimized to eliminate any bowing under pressure. Stainless steel pistons lower the amount of heat conducted into the brake fluid, and for racing, even better Wilwood Thermolock two-piece thermal barrier pistons can be optioned. Race spec versions also incorporate anti-knockback springs to keep the pistons close to the rotors and minimize excess pedal travel under extreme use.
Today's opened wheel designs also showcase the brake components, so Wilwood offers 25 different finish options for the latest Superlite calipers. Henry opted for a light Chicagoland Gray powder coat with blue logos, which matched the Z06's color scheme perfectly. But the beauty of the finish isn't skin deep; all 24 powder coat color options are applied over the Type-III hard-anodized treatment shared with Wilwood's race calipers. The finish is applied inside the piston bores as well, decreasing wear and drastically increasing service life. Some Superlite caliper part numbers can even be optioned with a polished aluminum finish, with the Wilwood logo laser etched on it, for street rods and show cars.
Follow along as Wilwood’s Mike Hamrick swaps the Z06’s trusty billet calipers for the new forged Superlites.
01. Introduced about 15 years ago, Wilwood’s Billet Narrow Superlite six piston (BNSL6) calipers were the hot ticket to big brake performance in a tight package.
02. Wilwood's newer Forged Narrow Superlite Radial Mount six piston (FNSL6R) calipers improve the previous generation's billet design by every measure, yet they are a direct replacement. (Kit P/N 140-8921)
03. Wilwood’s venerable BNSL6 calipers served Henry’s Corvette Z06 well over the past decade-but never happy to rest on their laurels-Wilwood thought it was time to upgrade.
04. Wilwood's Mike Hamrick began the swap by removing the old front calipers from the spindles of the 2004 Corvette.
05. Next, Hamrick removed the central bridge bolt, nut, and spacer tube from the caliper.
06. With the bridge bolt removed, Hamrick pulled the pads from the BNSL6 caliper. The same pads can be reused with the new FNSL6R calipers, but we chose to install new pads with the latest friction compound.
07. The FNSL6R caliper (left) is a direct replacement and fits in the same envelope as the BNSL6 caliper and under the same wheels.
08. Hamrick removed and cleaned the radial-mount shims before reusing them.
09. Since the FNSL6R is a direct replacement, Hamrick used the same shim stack as the previous caliper.
10. Hamrick slid the FNSL6R over the mounting studs and removed the center bridge hardware.
11. With the bridge bolt removed, Hamrick slid fresh pads into the calipers to check clearance and fitment.
12. Everything checked out, so Hamrick continued by removing the caliper and lubricating the radial-mount stud threads with machine oil (check the datasheet supplied with each kit, some do not).
13. Hamrick removed the brake hose fitting from the old calipers and replaced the pipe thread sealing tape.
14. Hamrick then installed the fitting into the FNSL6R caliper and oriented the fitting to meet the flexible brake hose angle.
15. With the FNSL6R caliper prepped, Hamrick slid it back over the radial-mount studs.
16. Hamrick torqued the radial-mount nuts to 30 ft-lb.
17. Then, Hamrick reinstalled the caliper bridge hardware.
18. After lining up the flexible brake hose, Hamrick tightened the fitting securely.
19. With the custom Chicagoland Gray powder coating with a blue logo, the six piston FNSL6R caliper is a massive visual upgrade and matches the Z06's color scheme perfectly.
20. Moving to the rear, Hamrick removed Wilwood’s old four piston Billet Narrow Superlite (BNSL4) caliper from the upright.
21. Hamrick removed and cleaned the spacer and shim stacks from the radial-mount bracket, then reinstalled them.
22. Hamrick checked the fit of the new four piston Forged Narrow Superlite (FNSL4R) calipers on the rear of the Z06. (Kit P/N 140-8032)
23. Hamrick removed the center bridge bolt and slid in fresh pads to check that the caliper was centered.
24. Even though the new FNSL4R uses the same brake pads as the previous BNSL4 caliper, Hamrick replaces them with new pads featuring Wilwood's latest friction compound.
25. With the fitment checked, Hamrick removed the new caliper and transferred the brake line fitting from the old BNSL4 caliper. Wrap with new thread tape, then tighten finger tight, plus at least 1.5 turns.
26. A drop of machine oil is recommended to help prevent thread galling with this kit (check the datasheet supplied with your kit, some do not).
27. Hamrick slid the rear FNSL4R caliper over the radial-mount studs on the caliper bracket.
28. The nuts are torqued to 30 ft-lbs…
29. ...Then the bridge bolt hardware is reinstalled.
30. Just like on the front, the rear FNSL4R calipers fit this Z06 perfectly - both visually and physically.
31. Hamrick then bled all the brake calipers, starting at the rear. Wilwood’s brake bleeder bottle makes this job a snap.
32. Be sure to bleed both the front and back half of each caliper, but only via the upper bleeder screws (air bubbles rise to the top of the brake fluid).
We are excited to see how this new brake setup performs at the next autocross event.