So I was reaching out to
Zeckhausen Racing to get the Ferodo DS3.12 for the OEM calipers, and told him that I was switching from Macan back to the OEM, and he asked if it was a race series issue or something else. Dave was super and has tons of information, and knows all things brakes.
He said that the master cylinder should be sufficient:
The stock MKVII caliper uses a single 60mm piston. That yields an effective piston area of 5655 mm^2. (multiply by two when the caliper is floating)
The 2015-17 Macon Base with 345mm front rotors uses calipers with four 42mm pistons, giving it an effective piston area of 5542 mm^2, or 98% of stock. That's close enough to be insignificant.
This should mean the brake torque output of your Porsche caliper upgrade would be 2% less than stock, but the stiffness of 4-piston fixed vs single-piston floater more than makes up the difference because of higher caliper efficiency converting hydraulic pressure into clamping force. The single piston caliper flexes way more, which wastes energy.
So I'm trying to understand why you had problems. Was 42mm the actual piston diameter of the Porsche calipers you had? Or something else? Was pedal travel longer, shorter, or the same as stock?
I told him about the issues that track users faced, such as initial brake pedal issues, and he said
That's a pad knockback issue. As you go through turns or hit the kerbing the front wheel bearings are deflecting. This deflection causes the rotor to deflect by the same angular amount. But when you are all the way to the outer edge of the rotor, that angular deflection turns into some significant axial deflection, which pushes the pads away from the rotors. The next application of the brake pedal has to close this gap, which is why you experience initial pedal travel without any braking.
If you were to gently tap the pedal with your left foot, just prior to when you actually need to hit the brakes, then you would find the pedal rock hard when you needed it. Alternatively, you could install StopTech pistons and anti-knockback springs in the Porsche calipers and eliminate the problem. The reason for the StopTech pistons is that they have a machined feature on the bottom that engages with the spring.
The solution looks like this.
He then suggested
the shortest pistons we have that support both dust boots AND knockback springs are 29.5mm. However, you could have a machine shop mill the bottoms of the OEM pistons for you. This is what it would look like:
So, the pistons that work have the shortest length of 29.5mm, so if that diagram is correct, the stock ones are too short. If someone can confirm the measurements that would be great. Otherwise I will be going back to stock in the upcoming weeks, and will try then to measure. His gut feeling is that they are 30mm, but we would need to get an actual measurement to know.
If the piston length is shorter than 29.5 and is machined, the springs to use are 8 of these:
https://www.zeckhausen.com/catalog/product_info.php?products_id=22044
This is the first time someone with some braking knowledge even tried to explain these issues. Sounds very interesting and would love to see if it solves the problem. Edit: There is a warning on the page that it can accelerate wear on pads, so that is something else to be aware of. This depends on the spring rate used. Dave said the .4in should not drag the brakes in a daily, and .6in could be used in a track car with severe knockback and should not drag the brakes in either case.
I would reach out to Dave and Zeckhausen racing for any braking needs/information in the future.