pormgb

Not too much brake for my car, I have cammed LS6 under the hood.

odb812

I'm still not seeing the correlation between hp and braking force. I understand that with more hp, you will be on the brakes longer in each braking zone, so heat becomes an issue. You should already be able to lock up the front tires with your current setup if it is well suited to your car, driving style, and type of event. Adding more hp does not give your front tires any more capacity to stop the car, so more brake torque is useless. It actually hinders you because you are making the range in which you can modulate the brakes before lockup narrower.

If you want to put a bigger caliper with more pad surface area further away from the center of rotation and adjust the bias accordingly, you could generate the same brake torque while generating less heat. But there is no advantage to adding more brake torque. Still the important questions are not being asked/answered here and that is front tire size/compound, brake pad compound, vehicle weight, how long your sessions are, and how hot your brakes are currently getting.

Take these two cars for example:
1. 300whp 951 club race car that weighs 2500lbs with 275 c51 front tires
2. 300whp 951 HPDE street car that weighs 3000lbs with 225 street front tires
Do these two cars have the same brake needs? But they both have 300whp...

JustinL

I agree. It's an energy in, energy out equation. Sticky tires, heavy vehicle, and of course how much speed you're scrubbing will put heat into the brakes. Shedding heat is done with ducting, and surface area. You can keep putting heat into the system until you hit a threshold of either your pad temperature or fluid temperature. That's how I think about it anyway. You can increase these thresholds with good fluids and pads more than with the size of the rotor/caliper.

Big brakes do look awesome though!

ninefiveone

Brakes are about heat management. More HP doesn't mean you are on the brakes longer. That's the mistake less experienced drivers make that I mentioned above. It means you are on the brakes harder. More HP means more speed means more energy means more heat. Brakes take motion and translate to heat.

So the idea that a caliper farther away from the hub generates less heat because it has more torque is largely incorrect.

The idea behind big brakes is actually about a bigger rotor being a bigger heat sink. Think of them like buckets. The bigger they are, the more heat they hold before overflowing.

That's why weight matters. The heavier a car, and the faster it is going, the more energy that will turn into heat.

It's not about whether you can lock up the brakes. That's a long misunderstood myth in car forums.

This is also why street cars rarely need bigger brakes. You have to drive very inconsiderately for a long time to overheat brakes on the street in most situations.

odb812

This does not make sense to me. How can more hp mean you are on the brakes harder? That means you were not driving the car to the limit before, when it had less hp. For me the limiting factor of how hard I brake is the limit of grip of my front tire. You can quadruple the hp of my car without changing the front tire and I will not be able to brake a smidgen harder, but I will have to brake for a longer period of time from the higher speed.

This idea is not incorrect at all. Assume the piston surface area and pad surface area stay the same. Further away from the center of rotation, it will take less friction between the brake pad and the rotor to achieve the same amount of brake torque. Less friction means less heat.


I'm not sure what you're saying here, but I think you're misunderstanding me. I'm saying if you're braking at the limit of the front tire, more brake torque will not help at all. I've driven cars with single piston floating calipers with street pads and EHP tires and I was able to brake at the limit of the front tire, so unless you have some big sticky tires in a very light car, that shouldn't be a problem with a 951.

That's not to say putting bigger brakes on a car won't help with heat or putting a more solid caliper will not help with modulation. In the case of modulation, most people will be faster in the end if they drop their monoblock caliper money on ~10 track days instead. As far as we know the OP's car does not have issues with heat. You won't know until you get out on track. On my other non-Porsche track car, I'm replacing my brakes with a second bbk to manage heat on the track. With the first bbk I was going through a set of carbotech XP12s in a little under 2hrs of track time. Each time I put a new caliper on the car, I'm not expecting to be able to get on the brakes any harder/later in any brake zone at operating temp, I'm just expecting not to exceed this temp during a session on track and get better pad and fluid life.

I've learned quite a bit about brakes, but most of it is from getting out there on the track every other weekend and driving, not speculating what I read on the forums. I've boiled my fluid before and I've even melted the back plate of a pad enough to punch a hole in it with the piston. I believe this more hp requires better brakes business is a forum myth. It might require better heat management, but most likely it won't if your car was well prepared to begin with.

KSira

I am tempted to try stock brakes with cooling ducts and brake plates with cooling. With SRF brake fluid and racing brake pads it might work fine as it is.

My car weights 1320KG, 265/285 tires, about 500whp.

Will test and report bake how the stock brake performs.

333pg333

Also remember that it isn't just the pad getting hot, the callipers also get hot, so having a larger monoblock calliper should assist in dissipation.

ps anyone noticed that the new 991 Cup brakes are a custom PFC product. Look very nice!

JustinL

The other part of the friction heat equation is distance over which it is applied. A larger diameter rotor moves the rotor under the pads faster which contributes to more heat being generated. It's much easier to think of it in terms of conservation of energy.

dmcampbell

Big Blacks and PFC 01's - way to go!

ninefiveone

More HP means higher speeds going into braking zones. Higher speeds means more energy that needs to be scrubbed off. The brakes have to work harder.

Don't take my statement on "on the brakes harder" as literal pressure. Harder can mean a lot of things depending on your setup. Higher friction pads, earlier braking, deeper braking, more cooling, whatever. Energy is energy. More HP means more speed means more energy means more heat.

Do the math on the lever arm with a bigger rotor, which is what you are referring to. You'll find it's not meaningful. Also, don't forget that a longer lever arm goes hand in hand with the outer edge of the rotor spinnig faster as it's size increases. The law of conservation of energy holds up as JustinL points out.

It's all heat management. Think of brakes as a bucket. When you get on the brakes, you pour water into the bucket. The bucket has holes at the bottom, that bleed out water over time. If you overheat the brakes, that's like overflowing the bucket.

Bigger brakes, better pads, better fluid, better tires = bigger bucket
More speed (and heavier car) = more water being poured into the bucket
shorter braking zone = putting water into the bucket faster
more cooling = bigger holes at the bottom of the bucket

We're actually saying the same thing, by and large. You're assuming that a car with more HP enters a braking zone at the same speed it did with less power. That can be the case, but most people use that extra HP to go faster.

s14kev

Nice bucket analogy. Must be science teacher.

odb812

I'm not assuming the car with more hp is entering the braking zone with at the same speed, I'm not sure where you're getting that from. I'm saying the car with more HP will not be able to shed speed any quicker. Take your car and see how fast you can stop 100mph - 0. Now put a bigger turbo on and crank up the boost. Now see how fast you can stop 100mph - 0. Same.

If the car is properly setup to begin with, it will be able to brake at the limit of the front tire. Therefore, the only way the car can shed speed faster(aside from driver technique), is by increasing the level of grip of the front tire. If you still have room to increase brake torque(pad compound, big brakes, etc) before hitting the limit of the front tires, then maybe you should have been focused on the brake system to begin with. I think learning threshold braking should be a requirement to graduate to more hp. I also think there are a lot more important things to consider in regards to your braking system than hp.

I like your analogies for heat, though.

ninefiveone

Ok

See?

odb812

So you made this statement:

in response to this statement:

that I made over 4 hours later. Do you care to tell provide any critique to the post I will make tomorrow?

Furthermore, I don't see how this translates to me saying two cars are going to enter a braking zone at the same speed. In your quote here, I'm talking about the rate a car can decelerate. I make similar statements in my other posts. I also mention the fact that the car with more hp will need to be on the brakes longer. I make no mention of speeds into braking zones. So if the two cars are braking at the same rate and the one with more hp is on the brakes longer then that means--drumroll please--the car with more hp is carrying more speed into the braking zone. You're arguing with me about points that I am not making.

ninefiveone

Sorry this bugs you so much.

Ok, let's focus only on your points.

You're focused on the rate a car can brake. Ok.
You posit that bigger brakes don't make a car brake any better in cases like 100-0. Ok.
You posit that a car with a proper brake setup will be able to brake at the limit of front tire grip. OK
You posit that if you can improve braking performance without increasing front tire grip, you should have improved the brakes to begin with (pads, etc), and that's irrespective of any change in HP. OK
A 951 has great stock brakes even with stock pads. Big brake kits don't really increase braking force because the tire was at the limit to begin with. Ok.

Based on above, we have this statement: "I believe this more hp requires better brakes business is a forum myth. It might require better heat management, but most likely it won't if your car was well prepared to begin with."

We also have: "As far as we know the OP's car does not have issues with heat. You won't know until you get out on track."

We also know the OP says they now have more than twice the HP they did before, but didn't have heat issues with stock HP at the track using properly prepared brakes.

For the purposes of this discussion, let's define properly prepared brake for track usage with an experienced track driver:
- Proper track pads that can handle high temps
- Proper brake fluid that can handle high temps
- Lots of cooling
- Great performing tires

So based on your logic above and the OP having 500whp, you're position is that he needs to get on track before he can tell if he needs bigger brakes; see above comment on more hp more brakes myth.

Anything I'm missing?