Feisty the "Family Car"

[Volumetrik]

This is going to be great. How do you deal with the thickness of the calipers themselves? IIRC, you need a wheel spacer to fit 47mm ET wheels.

 

[Dialcaliper]

Into the meat of the engineering design process.

Using the spare Mk8 hubs that didn’t work out the way I wanted on the car (but have correct caliper mounts), I was able to measure and mock up the brakes off the car. It is a tight fit - the caliper needs to sit about 2.125” from the rotor face which starts at the same offset as the stock rotor

Lots more measurements, CAD, making two dummy (non structural) brackets. Then another complete redesign from scratch, finite element analysis to show a greater than 10:1 margin on yield strength for long term durability and one 3D print test later, I came up with a final design to start cutting. It pays to prototype and iterate to get it damn right.

Crude CAD based on hub and rotor measurements - just enough to capture all the critical interfaces to design the bracket:



FEM Stress and Displacement. Always take these with a grain of salt as they’re only as good as the inputs you give them. So I left plenty of margin on material strength



Test 3D Print in plastic:


I decided this was as good a time as any to bust out the fancy bar of 2024-T8 high temp, high strength aluminum scrounged from my old job that I’ve been sitting on for something like a decade in the garage trying to figure out what to do with. It has 1.5x the yield strength of the typical go-to 6061-T6 that aluminum most stuff is made of, and maintains higher strength at 150C than 7075-T6. In other words, this is a perfect application.



A couple weekends and evenings later, and I have finished brackets! The Mk8 hubs are slightly different where the dust shield mounts so I ended up having to clearance the ends a bit. The final brackets are fairly chunky, about a pound each, but the Boxster calipers are light, so probably still less than the stock iron calipers in total.

Brackets:


Weigh-in about 500g:

Partly because Alloy 2024 is less corrosion resistant than 6061, and partly because I just like machined aluminum parts to look sexy even if no one but me will ever see them again, I went for hard anodize (for corrosion resistance) with blue dye (for more awesome) again, because for some reason it’s not as common a color and I liked the way they turn out. This time the anodized left the parts in longer so they came out a deep navy blue color. At first I was hoping for a lighter shade, but the navy blue has grown on me and isn’t that far from the car in Kona Blue. Threw in the 3/4”x1” shift pedal spacer I made a while back as well since anodizing is a lot charge up to something like 20lb of aluminum parts.

Fresh from the anodizing shop:


I designed the parts from the beginning to accept helicoils for extra strength and to stand up to repeated installations (required to swap the rotors)



Brackets with ARP Stainless bolts to the hub:


Final mockup with finished brackets:


Inside:


Rotor and Pad Alignment. Grade 12.9 bolts into Helicoils for the caliper to avoid the OEM Porsche Torx bolts which are not reusable:


What’s left is roughly 6-7mm to clear the wheel weights, which confirms that by a hair it would be difficult if not impossible to fit the 324mm rotors, by a hair. Would need that number to be at least 15mm clearance to work (basically talking 17” wheels at that point).

The Porsche calipers clear with basically the minimum 2-3mm to spare to the 16x8” 42ET Dekagrams with no spacers. Which I why I went through so much effort to get it perfectly aligned. My winter wheels actually fit even better because I opted for 35mm ET 16x7’s that put the outer sidewall similar to the Dekagrams instead of a closer to stock option.

Spoke and Barrel. “Porsche” is etched into the caliper anodizing, so it will just stay. I actually kind of like that they are grey and not bright red like the Boxster “S” calipers. My car came with silver stock calipers (despite also coming with black wheels) - I don’t care for a ton of exterior bling.



Inside:




Unclear if the PBR calipers would have fit with the bigger 324mm rotors. I’d have to just buy calipers and rotors to check the fit.

 

[jivenene]

Outstanding! Thank you for doing a write up with all this detail, instead of 2 second chooped up clips in a useless TikTok video!

 

[Dialcaliper]

Finally mounted up to the car after some fiddling. Opted for ARP stainless bolts with a coarser thread pitch to bolt to the knuckle and 12.9 socket head screws for the caliper (ARP heads are too big for the caliper counterbores)

Because Brembo, the calipers will accept either a flare fitting, or there’s a machined flat that bolts right up to the stock FiST 10mm banjo brake lines. I did need to source some extra short 18mm length banjo bolts (from GKtechif you’re curious) to avoid bottoming the bolt before the banjo is fully clamped

Bracket mounted and stock style (Mountune) banjo lines attached with 18mm long banjo bolt


Calipers and rotors bolted up:


Almost there:


To round it all up, I got G-Loc to send me some R10 compound pads for the track, as well as some GS-1’s for the street.

G-Loc R10’s - forgot to take a photo with the stock pads, but they seem like they have meaningfully more pad area


Drove the R10’s for the trackday and impressions are awesomely positive. The pedal is extremely stiff in a good way with Endless RF650 fluid. The pads modulate and stop really well, and they stood up to all the abuse I sent them. With the Nankangs warmed up, I got little to no ABS triggering.

Forscan Bleed Time!


The only downside is that the R10s squeal like a banshee when coming to a cold stop on the street. Hopefully the GS-1s will be better, but I did paint myself into corner slightly with the RB stainless pistons, as their larger ID means the factory Porsche pad dampers will no longer fit. There are some other things I can try for the street.

They roll! 16x8 ET42 Dekagrams. No spacers, just barely fits!


I feel like the extra rotor mass and vane area definitely helped, as I exercised the brakes pretty hard on the track without fading, even without extra brake cooling measures like some people have. At Sonoma I don’t think I’m hitting too much over 100-110mph, so that equation might change on a faster track like Laguna Seca, or if I ever get around to installing a LSD and/or upgrade to a Hybrid turbo, but I’m absolutely thrilled with how they turned out!

Braking deep at Sonoma (not quite NASCAR slicks late by the rubber marks though!)