Okay, I found a source for these pistons and some other interesting information. They do have two versions of the same piston, one is part number P42045A and the other is P42045A-B, and the later indicates it is for the Audi Q5 while the former does not specify a particular vehicle:
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I could not find a piston kit for the 4 pot Macan anywhere, but the Q5 no problem. And when you look at the complete rebuild kit for the Q5 they are all the same dark finish:
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So then I went looking for a good picture showing the pistons on both sides of the Q5 caliper, and sure enough the Q5 version does indeed use the same dark finish pistons on both inner and the outer:
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While the picture of the individual pistons is the same, I bet the non B part number is the lighter finish used on the outer caliper of the Macan. I sent a message to the supplier to see if they can confirm this, but they are the same dimensions and indicated material, so what else could it be? This seems to indicate to me that the different finishes are not about temperature, but about tuning displacement through pad retraction. For whatever reason Porsche wanted more displacement retraction on the Macan than Audi did for the Q5. Which is why they only did two of the four, apparently four would have been to much, but splitting the difference was just right?
As I said when I initially tested these RPV's I was only looking at the outer piston retraction assuming both inner and outer would be more or less the same, and that was a mistake. When I installed the 4 PSI valves and looked at the outer piston retraction it looked okay, but when I installed them and went for a test drive I was clearly getting pad drag, which I now realize must have been from the inner pistons which have considerably less retraction.
Regardless, all this tells me there is definitely more pedal height/response left on the table with my current setup. I have ordered a set of these pistons and also plan to do the custom cross over so I can swap the calipers. I will not do that until the pistons show up and this will allow me to do some more precise bench testing at the same time. I have several configurations I want to try and see what yields the best result, and bench testing will make this very easy to do. What I plan to try:
1. All four pistons with the slicker dark coated pistons with and without the 2 PSI RPV.
2. All four pistons with the slicker dark coated pistons with and without the 2 PSI RPV with piston seal lube applied.
3. All four pistons with the lighter coated pistons with the 2PSI and 4 PSI RPV.
4. Also test seal lube with the lighter coated pistons.
Based on what I have already observed, I am thinking the dark coated pistons with 2 PSI valve will work best. But who knows maybe just one complete set of either coating and some seal lube will do the trick. Or maybe the lighter coated pistons all around with the 4 PSI valves, that would give better track pad knock back resistance so...