Brakes- Number of pistons ?
 

Stainless Steel Brakes Corporation (SSBC), has sponsored a complete brake system for my Cobra upgrade build.

Although the car will be mainly used on the street, I will be racing large & small parking lot road course's, to racing in the Sandhills Open Road Challenge (SORC) in Nebraska, Kansas Motor Speedway road course, and possibly the Nascar oval in Iowa.

I believe the 6-piston front's would be overkill, even if they would fit inside the 15" wheels, so the question is, what number of pistons should we use front & back ?

I assume,
Front- 4 ?
Rear- 2 ?

Which brand & type of pads (if not from SSBC) ?

Kevin,

It's hard to tell from your post whether you've figured out everything about your brake system except the number of pistons, or if you think that is the only brake system issue that matters. The most important thing about pistons is the total area they cover. A larger number of smaller pistons merely allows you to get more total piston area inside a smaller diameter wheel than a large piston would require. ... So I suggest you get whatever number of pistons in whatever size they need to be to both stop your car and fit within your wheels.

If you haven't figured out all the rest of your braking systems requirements (e.g., rotor diameter and thickness for stopping torque and heat dissipation, pad material, master cylinder diameter, pedal ratio, etc.), you need to do that before you finalize your piston decision.

Old car magazines used to refer to "swept area" on brakes. I am not sure what if it applies to disc brakes or only drum brakes. Might be worth finding out.

A friend put yellow EBC brake pads, rotors and stainless lines on a Hummer and it was like about the truck weighed 1000 pounds less stopping.

Russell

The short answer is four each corner.

The long answer is what is this car doing 85% of the time? If it's a track car, then full on race brake are the issue. If it's a street car with some track time, then donor brakes could be done - PBR fronts all around, with good pads.

As for rotor diameter, it depends. Larger wheels are actually the result of huge rotors, and that implies a lot of high speed braking to nearly a stop. That would be road courses with long straightaways and sharp turns. Tuning the chassis could improve things a lot, tho, step up the G force it can tolerate, you don't have to brake as hard.

There is a lot of interrelationships with the other chassis factors and how it needs to handle.

So, what is this car doing 85% of the time? Get that numerically expressed as accurately as possible, then let that guide how to build a brake system, rotor size, number of pistons, etc. Don't let one feature be the most important priority when in fact it's only one small part of the overall system design.

SSBC is sponsoring a set of brakes for your Cobra? Huh! Why is that?

That being said, if SSBC is sponsoring a set of brakes, do they not have some technical advice to guide you? I'd be asking them what I should use.

DD

Hey, that is good question.

Russell

I have a letter of intent from the VP of SSBC for a brake system for all the advertising I'm doing for them. The details of the appropriate system will be discussed in about in 2 weeks, when the gentleman I'll be working with returns from vacation, so I want to be ready to speak options.

I would assume it's going to be a 4 piston up front and 2 in back. The VP mentioned if I'm not happy with their brake pads for my application, feel free to choose another brand or type.

I'll fit as large of diameter and thickness of the rotor as a 15" wheel is capable of. The slave cylinders are 1" and 1.375".

I'd say use the biggest rotors you can fit in your wheels......

I use 4 piston calipers on all four corners of my race car and Porterfeild pads..

You'll also need a rear proportion valve and some expirementing to get it set so you don't lock up the rear brakes...

David

I don't think you will be able to fit any 6 piston caliper inside a 15 in wheel----
the four piston calipers are thick and will determine the offset/clearance needed in your wheels--
A two piston floating caliper will give you the most room inside your wheels

Are you saying the MASTER cylinders are 1 and 1.375? if so you probably won't be able to push the 1.375 enough to stop-----are you meaning the rotors are that thick????/ doesn't make sense that the slave(calipers would be that size)

Yes, I'll correct myself. Those sizes are the masters.
I agree, I'm sure only the 4 pistons will fit in a 15" wheel. Someday,... when the selection of 15" tires are virtually nonexistent, I'll step up to the 17" for better tire selection and possibly larger brakes if needed. But I doubt I'll need more. If the car was primarily used for road racing, it would be a different story. In fact, the whole car would be different with a small block, IRS, 4-speed tranny, front air dam, different side pipes, larger/wider wheels & track tires, etc......

As far as the rotors, I may just get the drilled and skip the slotted. What do you guys think ?

drilled rotors will get stress cracks around the holes---slotted lets the gas/hot air escape

Smart thinking.
Thanks.

Ditto Jerry's advice. Go with slotted rotors, 4 pot calipers all round. Master cylinders 1" or over are too large without power assist. You should be looking at 5/8"-3/4" masters. This works well on my GT40 for track days. Also get street and trackday pads, otherwise you're compromising both.

Larger and thicker rotors do two things.

They add to the unsprung weight which is a negative in handling.

They also add to the the rotational mass which must be stopped.

Light weight is what you want.

Also the calipers are part of the unsprung weight.

1" on the front brake, 7/8" on the rear and the 3/4 on the clutch.

What thickness then ?
Shouldn't we be concerned going too thin and warpage ?

A lot of new cars today have thin & cheap rotors and warping is a big problem.

Just for info... this month's edition of Kit Car Builder magazine has an article discussing brake choices. Size, # of pistons, pad selection, differences in brake fluid...all are discussed. Not an exhaustive detailed explanation, but a pretty good overview. Swept area is well explained, as is master cylinder diameter choice, machining to the rotors, pedal geometry, etc.

When you are using your car on the track, you have much more to worry about than warping. ... There are two opposing issues at hand regarding brake rotors. First, the act of slowing a high speed car involves converting the energy of motion (speed) into the energy of heat. That heat shows up in the brake rotor and other nearby components, and is dissipated mostly by air flowing around it. If you are on a track that requires frequent hard braking, the heat can build up faster than the air can take it away. In that case the rotor is the primary heat sink for holding the heat and can get very hot (i.e., glowing red). Repeated heat cycles can cause some rotors to crack, fail and come apart. For these reasons you may consider an especially heat resistant and massive rotor. Or you may need to change rotors frequently.

On the other hand, everything that was said before about large rotors requiring more power to accelerate and more stopping force to slow down is true too. So larger rotors make a race car slower. That is why many real racers have gone to expensive and lightweight carbon rotors. They give the best of both worlds on the track, but can be problematic during street use due to low temperatures.

My guess is that for your situation (i.e., an occasional track guy), you value safety and convenience above maximum performance and cost. In other words, you'd rather not be buying and installing expensive light-weight rotors on a regular basis. Therefore, I suggest you not worry too much about the weight of your rotors and get some that the manufacturer says can stand up well to occasional track days.

Altho heavy rotors are more difficult to accelerate and decelerate---the quickest way around a track (TIME---TIC

The advantage of multi piston brakes is the ability to control pad taper. You tailor the clamping force with piston diameter.

Contrary to popular belief, Yes, a 6 piston caliper and larger rotor can be packaged to fit inside our common 15” wheels.

http://www.clubcobra.com/photopost/d...m/IMG_0511.JPG
http://www.clubcobra.com/photopost/d...0514_SMALL.JPG

This is a Wilwood SL6R on a 12.75X1.25 Rotor inside a front Trigo.
So long as you keep the rotor near the spindle, there is no problem with clearance.
However I will say, for all but the extreme high speed open track cars, few need parts this big. Ultimately, you would want the smallest, lightest system the can repeatedly stop the car from its highest speed, without fade. Obviously, a 300 hp street car that sees a little open track time, has a much smaller requirement than 3170.

Imo a 4 piston caliper and 12”x.810 rotor would be more than enough to deliver all the braking performance you could want with less weight and at a lower cost. Just get your pedal ratio and M/C bore size correct and you’ll be happy.


IMO, for the money, there are better brake packages than the the SSBC deal.

JASON