We know what you're thinking: "Ugh, another re-run?! I've already read this story!" But wait, because your eyes are deceiving you. Yes, we started with a Wilwood big brake kit for our LFX-swapped Miata endurance racer.
And yes, we then went to an even bigger brake kit with proper cooling ducts. But even that wasn't enough to handle …
We know what you're thinking: "Ugh, another re-run?! I've already read this story!" But wait, because your eyes are deceiving you. Yes, we started with a Wilwood big brake kit for our LFX-swapped Miata endurance racer.
And yes, we then went to an even bigger brake kit with proper cooling ducts. But even that wasn't enough to handle 300 horsepower, aero, and lots of grip from 15x10-inch wheels: Let's put the Miata under the knife for its third and final big brake kit.
How Could We Possibly Still Have Problems?
When we first swapped our Miata, we upgraded to a (since discontinued) Wilwood Forged Dynalite Big Brake Kit.
But it just wasn't enough: After multiple laps at full pace, the brakes began to fade. So we called V8 Roadsters and ordered its NA/NB Miata Wilwood Big Brake Kit, and paired it with a set of three-inch brake ducts from Singulär Motorsports.
This solved our fade problem, and would have been fine if we were sprint racing… but we're endurance racing, and that brake kit had an achilles' heel: Pad life. Even after experimenting with a few different compounds, we just didn't see a path to getting a full race out of a set of brake pads.
So why not just change them? Because we figured with one more brake upgrade—number three, for those keeping track at home—we'd finally be able to race all day at full pace without touching our brakes.
Massive Pad, Meet Massive Caliper
Our ask of Wilwood was simple: "What's the most pad we can fit on the front of our car while still running 15" wheels?" Their answer? The all-new XRZ4R caliper, which promises to be lighter, stiffer and better than their other comparably sized options.
Compared to the Dynapro radial-mount calipers we were running, these are about a pound heavier. But a pound here or there wasn't what we focused on: We were focused on pad volume, measured in cubic inches.
Our original big brake kit used 2.1 cubic-inch pads, while those four-piston Dynapros used 3.0 cubic-inch pads. These new XRZR4 calipers use massive 4.9 cubic-inch pads, nearly doubling the amount of pad we're carrying around the race track with us. That should, in theory, solve our problem.
What about the rear?
Our problems weren't limited to the front: The rear brakes were also chewing through pads, so we went bigger out back, too.
We were racing on Wilwood Powerlite calipers, and instead switched to Wilwood's four-piston Dynapro lug mount. That bumped our rear pads from 1.8 cubic inches to 2.1 cubic inches.
Switching rear calipers also meant upgrading rear rotors, and the car would now sport Wilwood's GT 36 Curved Vane rotors, each 11.75" diameter, 0.81 inches thick and vented. Bonus points for being able to use the same spares on the front and rear of the car.
Tying It All Together
What do all of these part numbers and pad measurements really mean?
This photo tells the story best. In it, you can see our new and old front pads on the left, followed by our new and old rear pads on the right. Finally, we should have enough pad material to race all day without touching the brakes.
Front:
Rear:
How did we attach everything to the Miata? Shoutout to V8 Roadsters here, who went above and beyond building us prototype caliper brackets and rotor hats to bolt on our fancy new front calipers.
In fact, our car was the development mule for their big brake kit based on these parts. If you'd like to copy our setup at home, you can do so for the fairly reasonable sum of $2740 for all four corners, plus your preferred pads.
What about fluid volume?
We've talked a lot about pads, but there's another thing to worry about: Fluid capacity.
We'll admit to not doing the math ourselves, and instead relying on Wilwood and V8 Roadsters to do it for us (hey, sometimes it's best to let the experts email back and forth before stealing the part number at the end of the chain).
Long story short: We now had more total piston area than the stock brake master cylinder was designed for, and far more area (and caliper leverage) in the rear. This meant activating our new brakes would require moving the pedal further, and the brake bias would need tuning. So we solved these problems with more parts:
First, we'd change our master cylinder bore size: V8 Roadsters sells a $251 master cylinder upgrade kit, which replaces the stock 7/8-inch diameter bore master cylinder with a 1-inch model from Wilwood.
This means equal movement of the pedal will push more fluid, which is perfect for our new calipers that take more fluid to move an equal amount.
We also installed an $81 master cylinder brace, which should improve pedal feel and consistency. And lastly, while we had everything apart, we installed a Wilwood brake proportioning valve so we could adjust our brake bias at will.
We topped off our new parts with a set of Wilwood's BP-40 brake pad compound and Wilwood XR racing fluid, then rolled the car out of the garage.
Did it Work?
We'd once again fired the parts cannon at our Miata's brakes—and our attic is now overflowing with big brake kits that only have one disappointing race on them.
Would this one be joining the pile? A test day at the Florida International Rally & Motorsport Park showed promise, so we brought our Miata out to another Lucky Dog Racing League event, this time at Atlanta Motorsports Park, for a real test.
We'll share the full recap of that race in our next update, but here's the headline: Even after a nearly full day of racing, we've got tons of pad material left. Why the word "nearly?" Well, because our day was cut short by an exploding transmission.
But that's a story for our next update. In the meantime, though, at least we've finally solved our car's braking limitations.
