frijolee

iTrader: (1)

I’m in the process of designing and having fabricated a 4 wheel big brake kit for the second generation RX7. The basic concept is to relocate the stock calipers outward and widen the fronts. This was inspired by the work of Roger Mandeville on the FD. I’ve already talked to Roger and gotten his blessing in running my own kit (now that's one cool older gent!). Special thanks to Howard Coleman and Charlie Shatzen for the referrals.




Front brakes test fit 1



Front brakes test fit 2 (shown touching the unmodified stock calipers)



Pad overhang = ~0.070"



Rear brakes:


There will be an official group buy in a while after the first round prototype pieces get thoroughly track tested. But for now I need feedback on what's important to you guys.

A first question is in the poll above. Please take a closer look at the pad overhang above. Feel free to leave any comments and questions you have in this thread but I'm really building this for myself and also decided to productionize so I can't promise to do all you ask for.


A few details on where I'm at so far:

-Rotors I'm designing the kit around are 12.75 x 1.18” front and 322 x 22 mm and12.68 x 0.87” rear.
-This probably means you'll run to run 17" wheels. I'll eventually produce a template folks can print out to confirm their wheel fitment like Stoptech provides.
-My intent is to let folks source their own rotors and I will provide mounting brackets and hardware. This means you can pick your choice of plain (like my test case), slotted/drilled, or full floating two piece.
-Some post machining will be required for rotors and calipers (required to maintain hubcentricity). I'll provide the drawings and detailed instructions on what you need to do but I'm not going to get into stocking rotor and caliper core inventory in my garage.


The best part:

-Upsizing all four wheels means that brake bias should be near perfect. Piston sizing is kept constant front and rear so the only changes in bias all come from rotor upsizing. The comparision of rotor size ratios means this kit shifts bias 0.5% to the rear. I’m assuming Mazda left more margin than this but running slicks on a race track might result in enough forward weight shift to increase the desired front brake bias. I have some pretty serious cars that will be helping me with track testing to confirm.
-Maintaining bias means there's no need to run an adjustable prop valve and there's no need to run an upsized MC.

I'm already in process of writing up a detailed comparison of the pros and cons of the various brake options available to FC's and their strengths and weaknesses (Evo brakes, Fastbrake kit, RacingBrake's new stuff, etc). However, at the end of the day I believe this is the best bang for the buck and set of compromises I could make.

Black91n/a

Are there straight vane, or better yet, curved vane rotors available? You mention two piece rotors, do you know of any that are currently available? I see those are pilliar vane, which aren't as good at pumping air through, and it'll add a bunch of weight, with a 2 piece it might just break even. Also, are you shure that it's possible to modify the caliper to get full pad contact without compromising the strength of any fluid passages or other parts of the caliper? If so I'd definetly be in the camp thinking that the caliper modification is better. Also, would it be possible for the overhung parts of the pads to come in contact before the pads are completely worn? I wouldn't think so with such a thick rotor, but it can happen with thin rotors (I've had to file pads on a race car to avoid this).

I'd expect this would be popular, since many people want big brakes, but FC owners are stereotypically cheap.

frijolee

iTrader: (1)

The two piece rotor is an Aero-rotor made by Stoptech so yes you'll have curved vanes. It'd be perfect for a max effort race car. (Pending the kind of brake upgrades you're allowed of course).

You should be able to trim the stock calipers without adversely effecting caliper strength. The force of the pistons creates a bending moment which attempts to force the seam open between caliper halves. This seam is held shut by the tension in the bolts and by the compression of the material beyond the bolts (opposite side from the rotor). The only material we remove is on the rotor side of the bolts and therefore not an issue.

However, you will have to be really careful to avoid sharp stress risers (hence why I'd do it with a dremel and a stack of sanding drums) but you definitely won't effect the oil passages. If I were building this one off that's what I'd be doing.

The Griffin

What's the total weight increase going to be between stock and the 1 piece rotor kits going to be ?

Black91n/a

I'd hope that with 2 piece rotors it's no more than stock, but at least it'll make for a bigger heat sink for more fade resistance if it's heavier.

BFGRX7

iTrader: (2)

If there's the option of a two piece rotor I'm all on this. Voted for Dremel process

~M

frijolee

iTrader: (1)

I'll grab a better scale from work so I can get you real numbers on weight.

sub9lulu

iTrader: (7)

it might be better if u cross post this in the main forum, alot of people doesnt come to this forum

be warned - rotards will give you bunch of BS

KNONFS

iTrader: (14)

How much for the kit? (more or less, as I see its on the prototype phase)

frijolee

iTrader: (1)

Pardon me if I defer on the pricing question as I don't yet have all the production quotes in hand. I'm buying material for the first round of prototype brackets tomorrow morning.

frijolee

iTrader: (1)

The first test brackets went out for fabrication this morning. I'm going with the full pad ultilization version.

KNONFS

iTrader: (14)

No problem, just keep us posted!

frijolee

iTrader: (1)

OK, here's where we're at:

Kit will consist of:

FRONT:
-Front brackets 6061-t6 Al (locate caliper in both radial distance and offset)
-Front spacers to widen the calipers (you'll get to trim the edges of the rotor slot to match this.)
-O-rings to maintain oil passages
-Longer caliper bridge bolts
-Caliper mounting hardware
-Drawings on what you have to machine to match rotor to hub.

REAR:
-caliper relocation bracket again 6061-t6 Al (which is more complex than the fronts)
-caliper mounting hardware
-2x hub centric rings to index off the rotor
-drawings on what you have to machine to remove drum e-brake portion of the rotor and to open up the index to match the hubcentric ring.

I'm supposed to get the first three sets of brackets back from cutting the perimeter shape today. I already have my test rotors machined. I already have myself set up as a wholesale distributor of the hub centric rings I need.

Still to do: I need to get the brackets post machined. I need to do some testing to see whether I need steel inserts on threaded areas. I need to pressure test the system to be sure the 0-ring compression and surface finishes are correct to prevent leakage. I need to complete the FEA analysis to be sure this will live in long term usage because aluminum gets tricky in fatigue. I need to finish bolt calcs on torque specs. I need to create wheel fitment templates so you can check these against your own wheels.

I need to finalize pricing (once I know cost on post machining I'll have a better idea on this). I think I need about a week before I start talking hard numbers and probably a month before I'm taking orders.

One of the big reasons for the delay is that I still need to set myself up as a limited liability company to cover myself in case someone wrecks while using these. It'll come with detailed instructions on what to do and not to do but these are brakes we're talking about here and I'm leaving some modifications in the hands of users so I'm trying to be careful.

KNONFS

iTrader: (14)

SOUNDS GOOD!

Howard Coleman

iTrader: (6)

++

CrackHeadMel

iTrader: (2)

Intreasting. I am going to look though some catalogs i have, however if people have links or part numbers for available rotors in the correct sizes for this kit.

Having a list of manufacters, part numbers, prices, options etc for the rotors all in the same thread would make things very easy for others.

Black91n/a

Or at least if we know what car the rotors are from it'll make it easier.

Are the fronts 05-07 Subaru WRX STi rotors?

frijolee

iTrader: (1)

I want to be sure I have a product available for sale before I give out the details on why I choose what and what I ended up with (rotors etc). I've gone to too much headache getting this productionized to have someone try to beat me to the punch. I can say I think I looked at the rotors from every last 5x114.3 performance car I know of to see what was out there.

All bolt calcs are complete and the big box of hardware came in yesterday. I got the first prototype articles back from cutting the perimeter shape little over a week ago.



I should get the brackets back from post machining this week meaning I'll finally be able to bolt a first article together.

Before anyone asks I'm pretty close to finalizing pricing as well, however, I should really pull the trigger on the status as an LLC first just to know how much a business license is going to run.


One big question mark I have is in regards to how much folks value the rear brake setup... I LOVE how the fronts are coming along but if it were just me I might be pulling the trigger on the corksport rear setup and running an adjustable prop valve. I'm going through with the rear design just to see if it can be done, but it's an important question.

Basically, this is the only rear rotor setup I've found that looks like it'll work well in terms of both relocation and thickness of rotor to maintain near stock brake bias.

That said, I've had folks point out that stock bias may be too far forward anyways. That said, I think I'm going to be pretty damn close to right. Running sticky track tires means you'll WANT more front bias (like came from the factory) because you'll see more weight transfer.

However, if you were going to run an adjustable prop valve anyways you could get just get the fronts from me and keep the rear brakes stock. This has the upside of keeping the potential to run a spare tire (you just might get to juggle wheels if the flat is in the front.)

As mentioned, my real quesiton in the rear is the value proposition of my rear kit relative to the corksport/attain rear kit. That uses a 315x20 mm rotor from the 99 rz rx7. The CONS of the corksport kit is that:

1) replacement rotors become a pain in the rear
2) you'll probably NEED a prop valve to get your bias right (still no MC upgrade though)
3) machining requirements are quit a bit harder because you have to pull the Mazda hub to have the 5 tips of the stud mounting face (see pic below) turned down.



HOWEVER the placement of caliper offset should actually be better than what I'm building.

The test rotors I’m using actually move the rear calipers significantly inboard so you have to do a bit of clearancing on the knuckle. I don’t know how much clearancing I need because it depends on deflection of the rotor/wheel bearing and mounting structure under load (same concept as what causes pad knockback). That’s one of those things I think I’m only going to find out on track.



You can see the tight spot on the lower mount. This is about 0.5 mm clear and I'm pretty sure it'll need more.


Worst case scenario it touches and I have to resurface the rotor. The test rotors are I'm using are 22 mm thick instead of the stock 20 so it might rub on the inside of the caliper bracket (only testing will tell whether there's enough margin there).

Finally, the added offset means my brackets have to mount on the backside of the spindle flange which complicates the part and adds cost. Cost on net for the rears is probably similar to what the corksport kit runs. The big upside of my version is in terms of bias, ease of rotor replacement, and a two piece rotor option, but I don’t know how important that is and whether it’s worth the negatives.

Your thoughts?

Black91n/a

You should make sure that the clearance won't change if the user still has DTSS. Maybe a small spacer between the rotor and the hub would be a reasonable solution? Personally, I'd rather see a bit more clearance there. There should be more than enough material there to grind another 1mm or so off of it to be sure.

Not having to machine the hub = excellent. That alone is worth a lot, as it'll cost money to do/have done, as most people don't have a hydraulic press and a lathe to do the work with, and that'll turn a lot of people off of the idea, because they can't be bothered or don't want to pay that much more for it.

Especially since this will likely be run by track junkies and the occasional racer, replacement rotor cost and availability is a concern, and if yours has lower cost and better availability then that's a huge plus.

frijolee

iTrader: (1)

Believe me, I'd rather see a bit more clearance too. Good thought on the DTSS by the way. I'll double check but I believe the DTSS pivots about the two pillow ***** buried in the joints you can see in the pic above via deformation in the third point of attachment toward the front of the car (away from the camera). If my thinking is correct this means relative motion at the tight spot won't be too bad.

Black91n/a

That was pretty much my thoughts too, but better safe than sorry. It's also worth checking what kind of bushing they're using there, if it's a spherical bearing type thing back there then there's no problems, if it's a bushing of some sort, then it might be a problem.

fc3s91

iTrader: (23)

Hey joel,
Im in as soon as you get all the r&d done.
Thanks Robert

HotRodMex

iTrader: (3)

I will be looking at the finished fronts. I have access to a mill to clearance the calipers, and since they are rebuildable I don't have to worry about doing the work again. However, I won't go for the rear as described. I, personally, do not want to have to grind down any part of the hub or knuckle. For the trouble, I would just go with the corksport and work on brake bias from there.

Black91n/a

I'd much rather grind a little off the arm than have to take off the hub and have them turned down like the Corksport kit requires (according to the post above). So just remember, while you might not have to grind the suspension arm on the Corksport kit, it's not a 100% bolt on kit.

HotRodMex

iTrader: (3)

Ahh. I misread.