8 PISTON Brake upgrade for Alfa GTA !

Originally Posted by Peter K

Tivia:


Front wheel horse power needed to get the 156 GTA to 155 mph (250 km/h)
0.000007 x 22.5 x 0.31 x (155 x 3) = 181,81

Front wheel horse power needed to get the 156 GTA to 168 mph (270 km/h)
0.000007 x 22.5 x 0.31 x (168 x 3) = 231,51

Front wheel horse power needed to get the 156 GTA to 200 mph (322 km/h)
0.000007 x 22.5 x 0.31 x (200 x 3) = 390,60

surely this perfectly demonstrates why enormous brakes are required for high speed braking as i assume that in basic terms the inverse is also true.

if the rear brakes do engage first, surely this preloads the car ie both ends will squat down on the road due to the dynamic loading, allowing more braking force to be applied even if only momentarily through all 4 wheels. obviously the load will transfer to the front pretty quickly but by this time a fair ammount of decellerative work will have been done. ok we all know the static loading is affected but by far the biggest effect is the dynamic load ie the resultant of the speed and the mass of the vehicle.

i've no idea what formulae are required [don't necesarrily care either] but assumming the suspension and wheel tyre combo is suitably set up there is no reason why a rear leading brake system is not going to work. how this is applied through the standard brake system and electrickery however is another matter, but in principle it has merit surely. although the actual bias may not be directly adjusted via the barking system changing the brake disk and caliper sizes will have some over riding affect on bias at least at initial bite if not throughout the entire braking range?

Originally Posted by GTV4me

surely this perfectly demonstrates why enormous brakes are required for high speed braking as i assume that in basic terms the inverse is also true.

It is not that simple. The reason that you need massively more power to increase top speed by a seemingly small amount is that drag rises at the square rate of the speed increase.

That drag actually helps - massively - with deceleration so the relationship between speed and brake size required to stop is in no way similar to the relationship between power and top speed. Even without wings many cars decelerate hugely on a lift, with no braking.

ok so proportionally its not as big a difference as indicated by the figures and as you say obviously the frontal area and drag help but the momentum you need to overcome for a car travelling at 200mph is greater than a car doing 155mph when decelerating. i take you point that the analogy was too basic though.

Originally Posted by Trailbraker

From my own Datalogging I certainly have increased my reproducable negative g by close to 50% from the OEM 305mm discs with 330mm DS3000's. (i.e. 0.72 Vs 1.1->1.2 g).
The 305mm brakes can brake at close to 0.9g.
Twice.
Then they go on fire.
..and are truely useless.
You need to keep them below 0.8g to avoid meltdown.

Cheers,
TB

I wonder how much of the performance increase is down to Pads/brake fluid? You have to consider that caliper piston size on the 305's and 330's are the same. both are 4 pot. Bigger pads alone does not add to brake torque output.

While i certainly agree that the 305's fade much much too early on the V6's, i still thought they produced about the same amount of G's

The 305 system is also considerably lighter and creates a lot less intertia. On my 2.0 TS the 305mm system worked really really well.. It was a good match for the car, no signs of fading there..

***Snipped from Brembo*****


What about size? Is bigger always better? "Not necessarily," the company notes. "There are many factors to take into account when choosing a performance brake system. First and foremost, a brake system must be designed based on the vehicle parameters and the type of use it will experience. Brake systems are designed to operate best within a prescribed temperature range. While modern high-performance friction materials broaden this temperature range from relatively cold pad temperatures to the high temperatures experienced in performance driving situations, the use of a disc that is too large will limit disc temperatures to the extreme lower end of this range. Not only will the disc temperature not reach the optimum range, but [the disc] will also be heavier than necessary."

Speaking of which, how does reducing the weight of the braking system enhance your vehicle? "The mass of any vehicle requires energy to accelerate or decelerate," Brembo says. "Reducing the vehicle mass improves acceleration and requires less energy to be dissipated during deceleration. Rotating mass requires additional energy in order to increase or decrease its speed of rotation. Therefore, decreasing the mass of the caliper is valuable, due to its contribution to total vehicle mass, and decreasing the mass of the disc has an even greater benefit, due to the fact that it must rotate as well. Additionally, the mass of the brake system is also unsprung mass. Reducing the unsprung mass has the additional benefit of improved suspension performance, resulting in enhanced ride and handling."

With OEM pads and standard fluid the 330 setup pulls almost exactly 1g repeatedly reliably, actually I really only got fade (before s/c but still modified) when I went to type-R tyres. Now this was with Autodelta cross-drilled 330mm discs which are very good, and don't warp like the 305 OEM ones but I don't think one could attribute the obvious additional braking forces to them compared to OEM discs.

Even a bog standard GTA will fade its 305mm brakes in two laps of moderately enthusiastic driving at my local track (which is hard on brakes). Its possibly that after even even one truely hot lap of 2.1 miles you could get them to fade to be useless if you really try to match 330mm braking levels.
This is based on three seperate 156 GTAs with 305mm brakes at mondello (AO'ers MArku-allen, Bmoferall and my own car when it was standard), so definitely a normal occurances with 305mm.
You really have to preserve them!

I'm sure race brake fluid would help the 305mm's, but not as much as changing the pads to something like DS2500's.
However, even then, the 305mm discs are simply to small to shed the heat generated, and glow molton red after a few minutes track use so obviously are a major limiting factor.
I would hate to think how short a time 305mm brakes would work for with type-r tyres..

Originally Posted by Peter K

I wonder how much of the performance increase is down to Pads/brake fluid? You have to consider that caliper piston size on the 305's and 330's are the same. both are 4 pot. Bigger pads alone does not add to brake torque output.

While i certainly agree that the 305's fade much much too early on the V6's, i still thought they produced about the same amount of G's

The 305 system is also considerably lighter and creates a lot less intertia. On my 2.0 TS the 305mm system worked really really well.. It was a good match for the car, no signs of fading there..

True.
..but Kinetic energy is also proportional to the square of velocity (See handy chart earlier in thread), so the brakes do have to work much harder at high speeds to contribute *their component* of overall decelleration.

As I mentioned earlier any effect of the braking system is in addition to the wind resisted decelleration.
i.e. the wind acts for the most part through the body of the car rather than exclusively through the tyres, so the total decelleration that the car can experience is the total of max braking effort plus wind resisted decelleration.

When braking from 155 mph on track you really are aware of how long it takes to get to a low speed. Even with the help of wind, big brakes (with proper balance) really come into their own at high speed due to the huge amount of kinetic energy they are able to efficiently absorb.

BTW our svelte Saloons won't decellerate quite as quickly as your race caterhams due to air resitance - those things have the aerodynamics of a shed at high speeds

Cheers,
TB

Originally Posted by jwyatt

It is not that simple. The reason that you need massively more power to increase top speed by a seemingly small amount is that drag rises at the square rate of the speed increase.

That drag actually helps - massively - with deceleration so the relationship between speed and brake size required to stop is in no way similar to the relationship between power and top speed. Even without wings many cars decelerate hugely on a lift, with no braking.

Good point TB. I agree with you.
I had to brake many times from high speed. Never had problems of wheel lock or balance. Even if it is difficult for some even to dream about braking in such speeds.

About the mass and weight of the caliper but most of disks what Brembo says thats truth. -Nice quote Peter-.

I have some personal experience about that. When we started looking about big calipers I had on mind the Monster 6 caliper from Porsche Cayenne. So my friend found me one set and one day I visited his place to have measurements for my car. But the same day he had an 8 piston Lambo front for another client. I was amazed about the size and hi tech of that caliper. Then I realize that this bigger 8piston was even lighter!!! we measure and the results was that 8 piston with pads lighter from 6 piston with pads-almost 3,5 kilos each caliper. 7 more kilos for both!!! And these was 8 piston much more powerful !!! I said forget the 6 piston Cayenne and we go for the 8 piston Lambo.
And the money difference was not even big.

SO as I wrote before he made all his fine work and after a month we placed the 8 piston to my car. On this time we did the job with the
original disks that lambo is using on the front. Big massive rotors 365mm * 34mm. He did the alu hats for Alfa setup 5*98 and some special work black anodized bells that was really beautiful as you can see on the photos. So we measure the weight of the disk and it was 12 kilos !
Not bad but not so good also . If you think that 330mm*32mm disks of the Big GTA set is 10 kilos each, 12 kilos for a 365mm with alu hats was not so big difference. And if I was on that Alfa set of 330mm maybe I wouldn't feel the difference so much, but I was on Brembo-Ferrari Maranelo 4 piston with 330mm Rotos with alu hats with about
5,5 kilos each disk. So it was a Big difference for me. The braking power was Huge but I didn't like the feel on my hands. The steering wheel was more heavier and Although the power of my car I felt like loosing some sec of acceleration. So I said to my Brake expert friend please start to search for lighter rotors. These rotors from Lambo are good for them. For this V12 and Weight maybe is fantastic and they need something real solid for all this power but for a lightweight front drive Alfa are too heavy.
http://img472.imageshack.us/img472/3...80large2tr.jpg
http://img402.imageshack.us/img402/7...2medium1xq.jpg
http://img402.imageshack.us/img402/2...2medium4wg.jpg

The rest on another post...

GTAFAN, what is the difference in weight between the standard 305mm system and the system you have now in your car?

GTAFAn, those Lambo calipers are Brembo, right ? They are very nice, monoblock, I bet they are light and quite hi-tech. How much do they cost, by the way ?
They would sure go well with some ceramic discs

5.5 kg 330mm discs would make a very nice improvement for the stock GTA system.. i just weighed a stock 330mm disc and it came out at 10.1 kg.

Originally Posted by GTAFAN

And if I was on that Alfa set of 330mm maybe I wouldn't feel the difference so much, but I was on Brembo-Ferrari Maranelo 4 piston with 330mm Rotos with alu hats with about
5,5 kilos each disk. So it was a Big difference for me.

5.5 kg would be nice, except the Maranello disks weigh 10 kgs too.. (p/n 184652) Alu Bell 330 x 32 bolt pattern 5x108

Which disc did you say you had then? the 5.5 kg bolt pattern 5x98 ?

I said Maranelo calipers but no disks . 300mm rotors with ALU hats made special for 5/98. That is 5,5 kilos .

But my 365mm disks (AP)that I've using now are 7,4 kilos with ALU hats made on 5/98 for Alfa. That is much lighter than the 330mm stock Alfa mono-block disks. And are 365mm !!!
So now you can imagine that 365mm disks in combination with the 8 piston calipers how strong can be.

Any way Pater as I can see you made a conversion from 2.5 V6 to 3.2 V6. You should place also the GTA master brake cylinder. Is also a big improvement and it works fine with your ABS. I have many friends here that did the same.
Also the rear calipers and disks from GTA are a bit bigger than stock 2.5 V6. That's also something.
But since you made some power improvements consider to find some rear brembo- GT2, GT3 rear calipers to fit at the rear. These are the only ones that can have the 305mm*28mm front disks from the 305mm small GTA setup. And you can place them on the rear.

Originally Posted by GTAFAN

I said Maranelo calipers but no disks . 300mm rotors with ALU hats made special for 5/98. That is 5,5 kilos .

But my 365mm disks (AP)that I've using now are 7,4 kilos with ALU hats made on 5/98 for Alfa. That is much lighter than the 330mm stock Alfa mono-block disks. And are 365mm !!!
So now you can imagine that 365mm disks in combination with the 8 piston calipers how strong can be.

Any way Pater as I can see you made a conversion from 2.5 V6 to 3.2 V6. You should place also the GTA master brake cylinder. Is also a big improvement and it works fine with your ABS. I have many friends here that did the same.
Also the rear calipers and disks from GTA are a bit bigger than stock 2.5 V6. That's also something.
But since you made some power improvements consider to find some rear brembo- GT2, GT3 rear calipers to fit at the rear. These are the only ones that can have the 305mm*28mm front disks from the 305mm small GTA setup. And you can place them on the rear.

It seems then that you get the best from both worlds in terms of braking power and unsprung mass.
Indeed the best GTA braking system i have ever come across.

Originally Posted by newalfisti

It seems then that you get the best from both worlds in terms of braking power and unsprung mass.
Indeed the best GTA braking system i have ever come across.

Not quite that simple.. The moment of inertia inceases by radius. While less unsprung weight is very good for handling the best of best both worlds would be to reduce the mass at the outer perimeter of rotating objects. This is why ceramic discs and carbon wheels are very effective. The bulk mass of a wheel and disc is unfortunately where the moment of inertia is greatest, and you can't really skimp on the material where the brake pads clamp, or at the wheels outer rim.

I know the theory very well . But I think to understand I must use the same words.
The mass at the outer perimeter of rotating from the ceramic disk from Enzo , 430 and carrera GT on 380mm is 6,75 kilos.The mass at the outer perimeter of rotating from my iron AP disks is 7,5 kilos.
I have only 750gram more weight mass at the outer perimeter of rotating than a ceramic set of disks !!!

These are from the lightest iron rotors available and are a special order from Aston Marting Racing team to AP racing!!!

So I know very well what I have !!! And what is bean used on the market , even with the most expensive ceramic supercar disks.

My Friend Brake expert just preparing a kit with ceramic disks from Maserati MC12 to be placed on a special production Alfa for testing here.