MiataSpeed is excited to announce a revolutionary new product in brake system tuning. Many people spend money on big brake kits, braided stainless steel lines, brake pads all in an effort to improve the pedal feel, and modulation characteristics of their brake system. What most people fail to consider is that the brake booster is the single biggest contributor to pedal feel and we've found that it is a largely unexplored tuning area.
As the pedal is applied, the vacuum in the right side of the booster is released and the absolute pressure rises. This causes a pressure differential across the diaphragm and causes a force to be added to the driver's effort. The ratio of the driver's input force to the total output force is referred to as the gain of the booster. As the pressure on the right side of the booster increases it will eventually reach ambient pressure at which point no more pressure can be added to that side. This point is called runout and is the most force that the brake booster is capable of producing. OEMs spend a lot of time tuning the runout of the booster to allow the brake system to be easy to modulate. By placing the typical ABS engagement pressure slightly past the point of runout the brakes are very easy to modulate. It takes a small amount of force to get to 90% of max braking and then a large increase past that to get to 100%. This means that if the driver applies any amount of force remotely near the runout force they will be very close to the max braking capacity of the car.
Enthusiast often install different tires, brake pads, rotors and even calipers all of which will change the line pressure required to lock the wheels. Often times we hear complaints from people who say that after a brake upgrade ABS engages a lot easier. The reason for this is that many modifications will cause the ABS engagement point to fall below the runout pressure. This causes the brakes to be very difficult to modulate.
To fix this situation we have designed a variable brake boost controller. By regulating the vacuum levels of the booster, we can adjust both the booster's gain and the runout point of the booster. This allows each driver to fine tune the pedal feel to best suit their driving style and car's modifications. By moving the runout point to just below the car's lockup pressure, the brakes will be much easier to modulate. The result is similar to changing the master cylinder sizing but that typically involves removing the booster which leads to much more difficult modulation. Additionally, changing master cylinder size is a time consuming, expensive and messy process which makes in not realistic to use as a tuning tool. Just like the launch is critical for a drag racer, the first instant of the braking zone is critical for the braking distance of a road racer. At the start of the braking zone you can simply stab the pedal and use the runout to get extremely close to max braking. With our variable brake boost controller you can easily fine tune your brake pedal performance to match the exact surface conditions and modifications to your car.
The Variable Brake Boost Controller can mimic anything from a smaller diameter brake booster (popular on many chassis where multiple boosters are available throughout model years), a larger diameter master cylinder fitted to the stock booster or a smaller diameter un-boosted master cylinder (while maintaining the drivability benefits of a well tuned runout point). The brake booster is an under-appreciated tool of aftermarket vehicle development but is the single most powerful knob within the brakes tuning toolbox.
To see for yourself what the product does simply get in your car and start it up. After letting the engine run for a bit take your foot off the brake pedal and turn the car off. Slowly press the pedal a few times and you will notice the pedal becoming firmer with each stroke. Each apply the vacuum level in the booster is falling both decreasing the gain and runout point of the booster. Our Vacuum Boost Adjuster allows you to pick any of the pedal curves you've just felt plus anywhere in between.
***It is possible to set the boost low enough that the driver is not capable of locking the wheels, SakeBomb Garage recommends that you step down from full boost in several increments and ensure that the brake system is able to lock the wheels at each step***
For a more detailed explanation about how a brake booster works, check out the video below: