A sliding caliper has to move the piston(s) twice as far as a fixed caliper does, that's why for the same pedal pressure you get the same effective pad pressure either way.

Pressure at the pad is determined by piston area and how much fluid is being forced in by the master cylinder. A fixed caliper has twice the area but moves half as much, a sliding caliper has 1/2 the area but moves twice as much.

@JRitt

Any chance you found some time to check the math on the bias?

Based on my research above and that online calculator, it appears that the Z32 calipers/Leg GT rotors combo changes bias slightly to the front (70.9 vs. 69.7%).

The variables I wasn't sure about were the pad heights.

If the above is correct, then I would think the experts would find that the brake bias is close enough to stock to consider this a successful brake upgrade. Care to comment on that (as you are the expert I'm referring to.. lol).

In fact, I was playing with the pad coefficients and found that you can run a Winmax W2 in front and W3 in back and it nearly perfects it to OEM standards.. Same thing with W3/W4, W4/W5, W5/W6. So running a slightly more aggressive rear pad can move the bias backwards a bit more and get it even closer to OEM.

so basically what we've discovered is that this "upgrade" is basically stock performance with a few more laps until you cook the pads?

I guess it depends on your definition of performance.

If you are talking about brake bias (ie.. front vs. rear clamping power), then yes.. these are basically stock. Based on my calcs (waiting for a professional to corroborate) they keep the bias within about 1% of stock.

If your definition of performance is clamping power.. then yes, these are similar to stock. Both setups have similar piston sizes and the same master cylinder, so they will press against the rotor with similar power.. Which is more than enough to lock up the rotors and engage ABS.

So for those two areas, these brakes are very similar to stock. But the exact same thing can be said for the high end Big Brake Kits.. they all try to keep similar bias and similar overall clamping power to the OEM setup.

However, there are a few major benefits to Big Brake Kits (that are mirrored to a lessor extent with these Z32 brakes).
1.) Light weight. These drop 8lbs on each side for the caliper. A blank OEM disk does add about 5 lbs back.. but you still have a net decrease in weight. A two-piece rotor would save even more if you want to spend the money on them.
2.) Better feel / consistency from fixed calipers: Quote from Wilwood's website - "fixed mount calipers that transfer PSI within the caliper into braking performance with a much higher efficiency are typically used on high-performance cars and for vehicles exclusively employed in racing for that purpose."
3.) Better heat dissipation: Having larger and thicker rotors will help disburse the heat. It might net you a few more laps if you are destined to overheat them.. Or, you might not overheat these brakes at all.. the larger heat-sink takes longer to heat up and more surface area allows for more cooling, so they might not ever overheat.. just depends on your usage.

I would say that these three points make the $600 investment well worth it. But everyone has their own opinion of course.

Oh.. and two more benefits just for fun:
4.) Cosmetics: These calipers look fantastic (especially after I shave the Nissan logo and put on the Subaru decal and paint them). The bigger rotors look great behind the wheel, and would look even better if you opted for drilled or slotted, etc.. For a big section of 86 owners.. the cosmetic improvement makes the whole thing worth it.

5.) Easy maintenance. Pad replacement is incredibly easy with these calipers since you don't have to remove them. You just slide out the pins and top clip and slip out the pads and put in the new ones.. easy!

Okay...we got a chance to look at the numbers. I'm still not 100% clear on the actual piston sizes you guys figured out on the calipers being used, so we ran all three scenarios. The disc was held constant at the 317mm diameter. We took a an educated guess on effective radius (which basically means where the center line of the piston is clamping on the disc).

If the piston sizes are 4x30mm or 4x26mm, the bias is way off. That's what caught my eye when I first read the thread. You'd be going from what we calculate as a roughly 67% front bias to a low 50% front bias. I'd definitely say to steer clear of doing such a swap. I would expect longer stopping distances than stock, as well as potential ABS issues.

If the piston sizes are 4x40.45mm (which is the number that was provided later in the thread and sounds more likely given the car from which they're sourced), then yes, the front bias is within a couple % of stock as eikond calculated. I would not expect any issues with ABS integration, etc.

If that's the case, you just have to look at all of the other variables that go along with the swap to see if it makes sense for your needs and goals (as described above).

A couple of further points for consideration:

Pads
The OEM front BRZ pad is what Ferodo calls an FCP1639 with the following dimensions (in mm):
137.5 x 50.1 x 17.6

The 300ZX front caliper under discussion uses a smaller pad, which is the FCP986:
119.3 x 49.5 x 14.5
So this one is about 20mm shorter and 2mm thinner. The 300ZX is a little more square though. The 300ZX is going to have a slightly lower overall pad volume and heat capacity, and provides the pistons with less insulation from heat due to the thinner thickness.

Also for reference (and this is an important one), the OEM FT86 pad in Ferodo's top racing pad compound (DS1.11) retails for $250.82. The DS1.11 in the 300ZX shape is $445.37...that's a $200 difference in price on every pad change! So you're going to have less pad material at a considerably higher price. I'm not sure what the pricing structure is for other manufacturers, but it's something to look into, particularly if you were thinking about tracking this setup. The real bugger is figuring out if that larger disc is going to net you any better of a pad wear rate vs. a stock pad on a stock disc, despite the pad having lower overall volume and thickness. Putting a number to that is darn near impossible with so many factors involved.:bonk:

Discs
Even though the discs do provide a larger heat sink, they aren't providing any greater efficiency (which is one of the primary functions of the disc in a purposefully designed BBK). If you buy a Centric 120.xx blank disc, it's still going to be a pillar vane disc that doesn't necessarily pump much air (see my previous long post above on heat transfer and evacuation). You also don't gain any of the benefits of an aluminum hat with regards to heat transfer or weight reduction.

As eikond mentioned above, you do still have a small net weight loss on the corner, although that is going to be offset by having substantially more rotational mass in the disc (which means it takes more energy/power to accelerate that larger disc vs. an OEM FT86 disc).

An easier pad change is a clear plus. Cosmetics would depend on the condition of the calipers you get your hands on and what you do with them (shave the Nissan off, paint them, etc. as eikond plans to do). If they're beat up from use or sitting in a junkyard, need new seals, etc. the rebuild would add a bit more cost as well.

Overall though, I have to commend eikond for creatively digging into the project and exploring new options.:thumbsup:

This is the case.. 4 x 40.45mm. I've found this data in multiple sources online as well as an eyeball with an unexact tape measure in my own garage.

Interesting point on the pad costs.. I hadn't considered this. I did a quick check on the project Mu NS400 pads and found them to be about $100 for Z32 and about $90 for BRZ. Interesting that Ferrodo is such a big difference.. This will probably be luck of the draw.. but something to consider before making any change.

Just to give more info. The pricing is very manufacturer dependant it appears. I looked at the pad choices I would choose from and found this (straight from Winmax and Mackin Industries websites).


Project Mu HC+800

Nissan/Subaru 4pot/2pot:
Front - $133
Rear - $89

FRS/BRZ (stock)
Front - $174
Rear - $145

Winmax W3

Nissan/Subaru 4pot/2pot:
Front - $145
Rear - $145

FRS/BRZ (stock)
Front - $145
Rear - $145

So as you can see Project Mu is actually significantly cheaper while Winmax is the same price. These are fairly common brake pads used on non-Brembo Skylines (R32,33, and 34), Mitsubishi 3000GT, and basically any Subaru with a 4/2 pot set-up that isn't Brembo.

Virtually every Japanese factory 4-pot made by Sumitomo uses this pad.

Also found on S14/15 Silvia K's/Spec-R, among other cars.

-alex

Just to continue the process of sharing information.. here is a look at the difference in size of the rotors from Stock OEM blank to Stock Leg GT Blank.

https://lh6.googleusercontent.com/-C...704_164546.jpg

https://lh4.googleusercontent.com/-a...704_164622.jpg

Jritt is correct about adding weight to the rotating assembly.. but I can't help but wonder if these do have more cooling capacity than he thinks.. Look at the width.. so much more space in the center cooling channels.. that has to move more air and help cool them better.

But its not a FWD car....how much of an issue is adding weight to the front wheels theres less overall weight up front...

This brake setup actually reduces weight to the front of the car..
The calipers are 6.1 lbs each vs. 14.1 lbs for stock.
The rotors (OEM Leg GT blanks) are 22lbs vs. 17lbs.

So the net weight loss is 6 lbs. The problem with this is that the lost weight is in non-rotating mass, while the weight gain is in rotating mass.. so it may have a detrimental affect to acceleration feel. I doubt it would be very noticeable, but I think from a pure math perspective, that weight is detrimental.

Some day when I'm rich I'll upgrade to set of lightweight 2 piece rotors and then I'll have a lot lower weight and better cooling, etc.. But that's another $800 or so?

COULD be made up in the wheel...but again its not FWD so I really dont see the "feel" thing making it into the equation. However hes not running a light wheel at all...

I see your point I think.. You are saying that the impact of increased rotational mass is less impactful since these are on the front wheels of a rear-whee-drive car.

Also it should be noted that running lighter wheels would/could offset the weight gain from these rotors.


Just an FYI.. I picked up another set of these calipers from a salvage yard. They were $35 each plus shipping.. so $85 overall. The rebuild kits run about $20. Here's an instruction guide on rebuilding them:
http://www.nicoclub.com/archives/reb...-calipers.html

I should re-title my thread.. $500 Big Brake Kit :)

:thumbup:

If you really want to have fun with this, the 94 + 3000GT Twin Turbo also came with these Sumitomo calipers.

40.4x2 + 42.8x2 piston setup in the front (From: Stealth 316)
38.1x2 piston setup in the rear

I don't know how the caliper bolts are spaced, but it's food for thought. :bonk:

94TT Centric reman calipers for $220 + $100 core charge (From: 3SX)

https://www.google.com/search?q=sumitomo+4-pot
https://www.google.com/search?q=sumitomo+4+piston

there's a lot out there.

-alex

I'm going tomorrow to see if I can find a set of these calipers.

The ability to change pads by simply pulling some pins is a big win for me.

The LGT disc will definitely have superior cooling vs. the OEM BRZ. I have no doubt of that at all. They have a considerably bigger air gap and far greater surface area. I was talking efficiency. An OEM-style blank will never have the efficiency of a good aftermarket design. You can make the air gap two inches wide, but if the vanes aren't shaped properly you're going to have a lot of turbulence relative to a design built specifically to move air. That's why a considerably smaller racing disc can run much cooler than a larger OEM-style disc.

With big brake kits, most of the kits on the market go about the same thing via two different routes. First would be the brute force method. This is typically the method employed by street BBK's. That means BIG disc and big pads. You use mass to combat heat. The second method would be efficient designs. That is the method used in racing. You use advanced technology and materials to address the heat issue at a far lower size/mass. As in every field, advanced technology is more expensive.

10-4 on the pad pricing info. Ferodo is the main brand we sell, so those are the prices I checked.

Good point about 3000GT and others.. What I don't know about those is the mounting ear positions.

They key to my whole setup is the KNS Brackets that adapt the Nissan calipers to the Subaru hubs and allow for the larger Leg GT rotors. What makes this a good swap is the fact that you can get the Nissan calipers for $50-$100 each.

It would be interesting to test a set of brackets from the other manufacturers to check mounting points. We also need to investigate used caliper pricing.

Thanks again for the input. Agreed on the concept of efficiency. Maybe a good layman's term would be "Cooling per pound". The newer, high tech rotors with upgraded materials, aluminum hats, and advanced vane design are clearly a better option. But you have to pay to play. As I've said from day 1.. if you can afford a professional BBK.. do it.. they are totally worth it! If you can't afford it.. then perhaps this setup gets you a braking upgrade at a very reasonable price.

@JRitt and @Dave-ROR Can I quote (with credits) what you've shared in terms of technical information? I'm going to write a part 2 to my article to summarize the past 4 pages of technical conversation. I still won't claim to be an expert.. but if you guys are ok with it I think I can share enough of your information to make it an interesting, informative and relatively accurate read. I want to give the pros and cons of this setup regarding brake bias, leverage, weight savings relative to rotational mass, fixed vs. sliding calipers, cooling capacity vs. efficiency, etc.. To do so properly I would like to quote you guys rather than simply paraphrasing. Is that ok?

Thanks again for all your time and info on this topic.

Yes eikond, absolutely. No worries at all. I'm happy to assist with the spread of quality information across what is many times a vast sea of misinformation and conjecture! :cheers:

IMO this is actually a negative of fixed calipers. Run some pads down a lot and then tell me they are easier :) Flipping up the caliper and using a c clamp is very easy and without the proper (and not really cheap) tools, you have to improvise with the fixed calipers. Not difficult granted, but time consuming and you run the risk of damaging the pistons (which is why a special tool exists).


It should be noted that the iron calipers might result in a weight increase (I'm not sure what the difference in weight is and I've only held/installed the aluminum versions).


Also, larger rotors move some mass further from the hub, making that gain more critical because that mass is rotating as well.


This kit isn't extreme but that's a big reason why I'd never suggest the stupid large kits of these cars (outside of looks).

Regardless of drive wheels, that mass still needs to rotate (and stop rotating) and the extra force is still required for that to happen. There's also a change in suspension function due to weight increases/losses but that's out of scope for this conversation.

The pistons don't suck themselves back in. I'd honestly rather changes pads in my sliding calipers than the fixed calipers I have.

Sure, listen to Jeff more though lol

http://www.ttzd.com/tech/brakestech.html

You can still use c-clamp or even a big set of pliers to force the pistons back in. You just have to do them a few times since when you squeeze one the others come back out a little bit. just keep rotating around until they are far enough in. I would just make sure the clamp or pliers had some kind of rubber cover or something to make sure you don't injure the top rim of the piston.

If you really had to do it in a hurry I'm sure you could find a special tool.. maybe even make one.

Just use the pad and push them both in at the same time with a c clamp.

Last time I did a pad change on a caliper like this, I used a flathead screwdriver between the rotor and pads and pried the pads open before removing the old pads.

Turkey basted the extra brake fluid out of the resevoir, dropped the pads in, done deal.

usually I just push the pistons in by hand. not sure if that's bad or not.

Same here. It's never been a problem for, but that's far from definitive.

I use old pads to pry them in to limit damage (visual and other). I still find a c-clamp once on an old pad with a slider to be far quicker and easier than at least twice, which is why I said sliders are easier to change. One time vs two minimum.

My calipers have fairly thin wall SS pistons, not thick aluminum ones so that's a bit more of a pain (literally ;) )

The only time fixed calipers is easier to change, is if the pad being swapped in is thinner than the pad being swapped out.

Otherwise, the next-best thing is to find a thin piece of metal, and "clamp" one side of the caliper first, insert new pad, and "clamp" the other side to compress 2 pistons at a time. This is the only way to push the pistons back in without playing the "whack-a-piston" game.

Versus sliding calipers, it is NOT easier if the pad being replaced is worn thinner than new pads.

-alex

sounds like ease of pad replacement is not an unanimous choice for fixed calilpers. I personally think it's easier.

For anyone who hasn't done it.. here's a quick video using Brembo's. They are the same exact process.
[ame="http://www.youtube.com/watch?v=DeXv9Knbkqw"]Tutorial: Change Front Brake Pads on 2006 Subaru WRX STi - YouTube[/ame]

so what vendor wants to package all of this together and sell it lol

I hope I get a cut :)

If any one vendor could do it would be KNS brakes. There are mulitple sources for the calipers, rotors, pads and lines. I outlined my choices based on price, service, etc.. But anyone could come up with those parts. The one part that makes it all possible is the bracket by KNS. So any vendor who wanted to do a package would have to buy the brackets from KNS. Or I suppose they could do the R&D and make their own. (or in this day and age, just send a set to China..)

I've written my second installment on this build.

Part 1 talked about what parts to buy and how to assemble what you need.

Part 2 is a discussion on the first 4 pages of this thread, highlighting the topics of debate such as cooling, weight savings, fixed vs. sliding calipers, and especially brake bias. I wanted to share some basic knowledge of braking systems and then discuss how this upgrade compares with stock. I tried my best to include some of the more technical details that @JRitt and others have shared and yet try to keep things simple enough for everyone to understand. In the end I give my opinion on how good this upgrade is and who it would benefit.

http://www.nicoclub.com/archives/300...rz-part-2.html


Btw.. I just published it. I'll sleep on it and then go back and re-read and try to edit for grammar and typos, etc.. So if anyone catches anything, please let me know. Especially if I gave bad technical information!!!

Thanks everyone!

Good write up.


For the pad height, just go measure the max friction height of the friction pad (not the backing plate, just the friction material). The BRZ pads up front are bigger so it'll change your numbers a bit. Not sure on the rears. Actually there is probably very little reason (outside of matching calipers) to even touch the rears. You won't get much feel improvement (ie I highly doubt that ANYONE here would even notice it) and the wear rate is already negligible in the back with the OEM stuff. Weight savings and consumables (pads only in this case) would be potential reasons but that will be a lot less in the back I'd guess than up front.

The pad height difference is pretty negligible to bias impact.

You are right about the rear swap.. It's basically no impact to performance. The Z calipers have the same pistons sizes so no change in performance. The feel from a fixed caliper is much less impactful on rear brakes. The disc is the same, the pad size might be slightly different, but not noticeable. You do go from 5.8lbs per caliper to 3.2lbs.. so 2.6lbs per side or 5 lbs overall... which is basically not noticeable.

I'm going to do the rear swap just to complete the package and complete the write up. Cosmetics are nice too.. so that doesn't hurt. Plus I already have the calipers. So yeah.. to be honest, I'm doing the rears for cosmetics.

I did say a bit, not change them a lot ;)