jimlab

I don't think so Max.

The master cylinder pushes a given amount of fluid with each stroke. The proportioning valve determines how much of it goes to the front brakes. Bigger/more pistons up front doesn't mean more fluid... it means less clamping pressure with the same amount of fluid. That's why you increase the amount of fluid being pumped by switching to a master cylinder with a larger bore.

ccw998

Why do I buy this 6 pot brake kit? because I tried their 4 pot brake kit in the WRX. Actually, I am not the professional driver or mechanic. I just use my feeling and experience to compare the stock and the 4 pot brake system in the WRX. It make the BIG different!!! It gave me SAFE feeling to drive the car in the street and the braking distance is much more shorter compare with the stock brake.

Also, A&Z don't make 4 pot for FD because this brake kit system is for Japanese Market only. Don't forget our FD is the TOP SPORT CAR level in Japan!!!

Railgun

But wouldn't you have the same force to the pads? Just because you're increasing the quantity of what you're pushing doesn't mean you're decreasing the line pressure. And the fluid within the caliper will be greater since it's a larger caliper. In addition, you have a larger surface area for friction, so I would think that it would take less pressure to have a similar effect over a stock setup.

jimlab

I seriously doubt that, unless you're talking about repeated hard braking under track conditions or similar use.

In a single stop from 60 mph, a big brake kit won't stop any sooner than stock brakes, and may in fact stop later due to less clamping pressure at the pad, assuming the master cylinder hasn't been upgraded also.

Even stock brakes have enough clamping pressure to lock the wheels, and at that point the weight of the car and the tires are what determine braking distance. Change to a stickier compound and/or increase the size of the contact patch or lighten the car and you reduce braking distance. The only thing that larger brakes are good for is being able to shed heat more efficiently, delaying brake fade longer under repeated hard use. The downside is an increase in unsprung weight.

jimlab

Think about snowshoes. You don't sink into the snow because your weight is spread over a larger area. In other words, the pressure at any given point is greatly reduced. Likewise, the same volume of fluid being pushed against a larger surface area (more/larger pistons) equals less pressure at any given point.

Actually, if you increased the volume of fluid that you're pushing, you would increase line pressure.

Greater static fluid capacity, sure, but that doesn't mean you're pushing more fluid with the master cylinder.

Larger surface area, but less pressure at any given point. See above.

KrisRX71993

So who sells these for that price?? id be interested in a set

rynberg

Jim (and everyone, for that matter):

http://www.stoptech.com/whitepapers/...erformance.htm
http://www.stoptech.com/whitepapers/...ing_valves.htm
http://www.stoptech.com/whitepapers/...ons_122701.htm

maxcooper

I understand where you are coming from, but I think you are focusing on the wrong thing (volume) and ignoring what really matters (pressure). I will start with volume, point out the flaw with the volume argument, and then explain why pressure is really what counts.

We know that the master cylinder has two separate but essentially equal-sized chambers from which fluid is pumped when you press the brake pedal. One is connected to the front brakes and the other is connected to the rear brakes. With the stock brakes, it probably takes about the same amount of brake fluid volume for the front and rear brake caliper pistons to push the pads into the rotors. After the pads hit the rotors, the braking force can be adjusted by varying how much force you apply to the brake pedal. However, if you then decide to install some front brakes with huge pistons, you throw the system out of balance. As you press the pedal down, the rear brake pads hit the rotor first. Your new 6-piston front calipers have 3 times the piston area of the stock front calipers, so the pistons have only moved 1/3 as far. Keep pushing the pedal, and the pressure starts to build quickly in the rear brake circuit before the front pads even hit the rotors. By the time the front pads do hit the rotors, the rear brakes are on the verge of locking up. Even though you've got mammoth front brakes, the rear brakes lock first indicating that the bias has shifted drastically to the rear.

I think this is the model you are working from, Jim. And it does make sense. But based on my experience of installing big front brakes and finding that the bias was shifted drastically forward (rather than backward), I figured there must be some flaw in this model. So I did some research and found a component called a pressure differential valve. This is a valve that joins the front and rear brake circuits (equalizing their pressure) unless one of them starts to lose pressure rapidly (e.g. burst brake line). I don't see any description of it in the Mazda factory workshop manual, however I believe that our "proportioning bypass valve" must join the front and rear circuits someow, since it wouldn't make any sense to have more than two hose connections to it (it has four) if it were a simple proportioning valve. I don't know if it has a pressure differential valve built-in, but I suspect that it does. So, the flaw with the volume model described above is that the pressure will be equal in the front and rear circuits unless something is drastically wrong (ignoring the presure reduction provided by the proportioning valve for a moment). You might argue that the pressure differential valve might not be able to distinguish the difference between a burst brake line and having giant front calipers. However, my experience with the AP 4-pot big fronts and the resulting change toward front bias leads me to believe that the valve stayed open (keeping the front and rear pressures equalized). Perhaps this threshold does not exist (and it doesn't matter how big your new front calipers are), or I was just under it, wherever it may be.

So, now we know that pressure will be equalized in the front and rear brake circuits even after a front brake upgrade, so let's see what happens. You've got your foot in the brake pedal hard enough to produce 1000 psi of brake line pressure. Your new brake calipers have twice the piston area as the stock brakes, so they are pinching the rotor with twice the force that the stock caipers would. And the radius of your big new rotors is 30% greater than the stock rotors. Your new front brakes are applying a whole lot more braking torque to the front wheels than the stock brakes did under the same conditions. The rear brakes are doing exactly what they would have done before your front upgrade (with the same amount or force applied to the brake pedal), so you find that your bias has moved far toward the front. The rear brakes don't feel like they are doing anything now.

Time to order the Mazda RZ rear brakes, or go even further and lose the parking brake (like me: http://maxcooper.com/rx7/how-to/brakes/rear/index.html). Or you can just deal with the bias being messed up, perhaps with a honey that is attracted to huge brake systems on your lap. Or you can sell what you've got and go all-RZ or get a StopTech kit designed to work with the stock or RZ rear brakes. Or you can make your car a show queen and never drive it (waste!). Or you could just swap back to the stock brakes.

The issue that the 929 master cylinder resolves is that the pedal requires too much travel and/or is too sensitive after installing brakes with more piston area. The 929 master has a bore of 1", versus the stock cylinder which has a bore of 15/16". I have read all kinds of reports, but its effects are very simple and merit no debate: when you intall a master cylinder with a larger bore size, you will need to push the pedal harder to get the same level of braking, but you won't have to move the pedal as far. In other words, the pedal will be "harder" or "more firm" than it was before. I am very happy with my switch to the 929 master cylinder.

-Max

fd3s777

iTrader: (3)

Hummm... very nice kit. A&Z factory is just right around my factory. Their 6 piston kit is very nice. But I think I'll go with these. Looking from it do they remind you of Gra*er 6? hehe... They came from same factory. I should have them on next month... Save $$$ for them... I'll put them on my white FD. Will look nice with my Work S1.

fd3s777

iTrader: (3)

BTW here is a 8 piston... Humm might be too big for my S1.

DomFD3S

JBT Brake System?

Where is the A&Z produced? And where is the JBT factory located? Kinda off topic, but I figured I would ask.

The JBT does look nice though...I must say!

fd3s777

iTrader: (3)

They are all from Taiwan. All OEM factories for Japan companies.

DomFD3S

Brings a new meaning to "Made in Taiwan".

rallimike

iTrader: (1)

Where are you guys finding this stuff? I can't get a hit on Google. You got a website with any info?

superior_force

again, the 929 master cylinder and steel braided lines will do more for braking performance (on the street) than any "big brake" kit

from rynberg's link:

BRAKE PEDAL FIRMNESS AND MODULATION

The human brain/body system modulates most effectively by force, not by displacement. The side control sticks on current fighter aircraft hardly move. The feel of the brake pedal should approach the firmness and consistency of a brick. There are several factors at work here:

1) Brake hoses: Optimum pedal firmness cannot be achieved with the stock fabric reinforced rubber flexible hoses which swell under pressure - decreasing pedal firmness while increasing both pedal travel and brake system reaction time. The first step in upgrading the braking system of any vehicle is to replace the OEM flexible hoses with stainless steel braid protected flexible hoses of extruded Teflon. Make certain that they are designed for the specific application, are a direct replacement for stock and are certified by the manufacturer to meet USDOT specifications. A claim that aftermarket hose are certified by the DOT is a caution flag. The DOT does not certify anything. Manufacturers certify that their products meet DOT specifications and legitimate suppliers can produce reports from DOT approved testing laboratories. When upgrading your brake hoses, replace both the front and rear hoses. Due to their swelling under pressure the stock hoses take a measurable amount of time to transmit pressure to the calipers. Replacing the front hoses only will result in a built in lag time to the rear brakes and may also adversely effect the microprocessor control algorithms of the ABS system.

2) Master cylinders and Caliper piston diameters: While it is true that the most effective master cylinder arrangement is the twin cylinder with adjustable bias bar that is universal in racing, replacing the OEM master cylinder on a road going car is simply not practical. When selecting an aftermarket system, make sure that the caliper bores are designed for the specific application.

3) Disc run out and thickness variation: Run out in excess of six thousandths of an inch (0.006") can be felt by the driver as can more than 0.001" of thickness variation and any amount of material transfer from overheated pads. Run out is caused by poor design of either vanes or the junction between the friction surfaces and the mounting bell, by poor machining, by thermal stress or by any combination of the three.

4) Caliper and caliper mounting stiffness: Clamping force tries to open the opposing sides of the calipers - resulting in a longer than optimum pedal travel and uneven pad wear. The only solution is optimal mechanical design and material selection - there is no effective development fix for "soft" calipers. Also, the stiffest caliper will be ineffective if its mounting lacks rigidity.

5) Out of balance discs (or tires): The driver cannot modulate the brake on a bouncing wheel. Compared to tires, disc diameters are relatively small, but all discs should be balanced. As the installation of balancing clips will interfere with airflow the preferred method is to remove material from the heavy side. Significant core shift in the casting (visible, as thickness variation on individual friction surfaces will result in incurable dynamic imbalance.

6) Pad "bite" and release characteristics: For efficient modulation the pads must "bite" immediately on brake application and must release immediately when the pedal is released. This is purely a matter of pad selection. It is seldom a good idea to use different compound pads front and rear and never a good idea to use a pad with more bite or a higher coefficient of friction at the rear.

thankfully, replacing the master cylinder on these cars is practical and fairly straightforward