• 2017

Big Brakes 101

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Despite the fact that the 426 Street HEMI® engine produced over 425 horsepower from the factory in the ’60s, it wasn’t very long ago we were celebrating the 300 horsepower milestone from a factory V6. Now, the Dodge Challenger SRT® Demon destroys all norms with over 840 hp.

If you’re buying big factory horsepower, you can expect the brake systems on said vehicles to also come with an equally impressive brake system. In fact, it’s mandatory. Engineers say that typically, if you have a vehicle producing 500 horsepower, the factory will build in about 1,000 hp worth of brakes.

This is important information if you plan to build horsepower either in a customer’s vehicle or in a vehicle of your own. Be sure to beef up the brakes when you beef up the power.

Mopar® offers “big brake” kits for certain application Dodge Challenger and Charger models, like the Performance Upgrade Stage 1 Pad and Rotor Kit (P/N P5160048) or the Big Brake Kit (P/N P5160035AB) that includes front rotors, pads, calipers, brake hoses, dust shields and mounting hardware.

For SRT/Scat Pack vehicles equipped with four piston brakes, there’s the SRT Hellcat Brake Upgrade Package that includes (red) six-piston calipers (front), four-piston calipers (rear), rotors, pads and hardware. And more kits are coming soon.

EXPERT OPINION

Erich Heuschele, Manager of SRT® Vehicle Dynamics and Manager of SRT Motorsports Engineering, took time during recent SRT vehicle aero thermal validation testing in Texas to share his thoughts on big brake kits. Heuschele is responsible for everything underneath an SRT vehicle (including the 800 hp SRT Demon) as it relates to brakes, steering, suspension, etc.

Heuschele insists that if you are adding horsepower to a vehicle, you must add bigger brakes too. “The brakes’ job is to take the speed of the vehicle and dissipate it by turning the speed into heat,” says Heuschele. “And the energy of speed is proportional to the square of the velocity.” What?

More simply, says Heuschele, “There is as much energy tied up in a snub from 65 to 60 mph as there is for a whole stop from 35 to zero. So the faster you go, you have a lot more energy in your speed. Since the brake system takes all that energy and turns it into heat, the heat is transmitted to the rotors. So a bigger rotor has a bigger area for the heat, or more thermal mass. More ability to absorb the heat.”

Now you could try to blow more cooling air at the brakes to raise the thermal capacity, or try bigger rotors, or a rotor that pumps more air (slotted or drilled). You need to be able to take out the heat that is being generated in the rotors while not over-taxing the brake system. A complete big brake kit does this work for you.

When it comes to rotors, there are differences. “For rotors, it’s my opinion that slots are better than cross-drilling,” says Heuschele. “Crossdrilled holes in rotors tend to crack when they get hot, which is why we use slots from the factory on SRT cars. The slots will still help clean the pad off, and help with fade resistance, but without risk of cracking the rotor when they’re glowing red. The rotors grow when they get hot, so the entire circle of the hole tries to grow, and it can produce high stress at the hole edge.”

PADS MATTER

Enhancing the brakes is not just about bigger rotors; don’t forget the role of the brake pads. “When the pads get too hot, they start to fade,” says Heuschele. “When they’re hot, they don’t generate as much friction. And the pads — since they’re so much smaller than the rotor — will follow the temperature of the rotor. By having a bigger rotor, there is more area to dissipate the heat and that keeps the temperature of the pads lower.

“A common upgrade is to put high-performance pads on the car, which works when they’re hotter, they don’t fade as easily,” says Heuschele. “But the issue with racing pads that work great at the high temperatures is they are not as effective at lower temperatures at street speeds.”

The comparison is racing tires. They’re designed for maximum performance at higher temps while on track. But race tires are not good when cold. Similarly, racing brake pads won’t work as well as stock pads when driving around the street when the pads are cold. They’re not in the optimum temperature range.

Having a bigger rotor allows for a more normal pad that works both on the street and at the track.

BIGGER CALIPERS

Another important ingredient of a complete brake kit is calipers. Bigger calipers allow for larger pads and that results in better wear due to the larger area on which to spread the load. “You need to upgrade everything,” says Heuschele. “And to move a bigger pad against the rotor, you need more pistons in the caliper pushing on it for even pressure distribution.”

“The SRT Hellcat Brake Upgrade Package (P/N 77072382) drops right on and uses all the same stuff from the brake pedal out to the caliper, including how much fluid you’re moving,” notes Heuschele. “You need to be careful if you use a generic brake kit, that with a larger caliper, with more and larger pistons, you can quickly run out of fluid volume. You would then need to upgrade the master cylinder to push more fluid to make sure you fill those calipers to get proper operation. That’s a mistake some people make. That’s why design is important. You can’t just put any big brake kit on, say, a Dart. It has to be engineered for that vehicle.”

MCG17US4_003Also, not every car has a high-performance brake on the rear. The Challenger Scat Pack has the 4-piston caliper in the back, so that’s good. But, some cars don’t have that, so you will also need to upgrade the back with the front to keep the system balanced.

“With a big brake kit on just the front, it requires less brake pedal effort,” says Heuschele. “The problem is, the rear is not balanced and the front is doing all the work. Pad wear is increased and then they run hot at the track.” You wouldn’t upgrade the suspension in the front only; the same goes for brakes.

Also important to remember in a well-balanced brake system is how it works with other technologies. “The better balanced the brake system, the better the ABS and ESC systems can manage the upgrade,” Heuschele says. “Those systems also use the brakes as part of their calibrations for dumping pressure when the wheel locks, so changing the dynamics really matters.”

It’s also important to note that rear brakes are often upgraded with no consideration for the parking brake. Make sure the kit you put on allows for a parking brake, especially when the customer expects a parking brake to work.

Why choose a Mopar® big brake kit? That’s an easy one, says Heuschele. “Mopar kits are developed and tested and validated on the car, rather than just something that fi ts. You maintain proper brake fluid volume and balance of the vehicle. Our kits are compatible with the calibration of the ABS and ESC systems.“

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