I have achieved a little bit of progress this week with the brakes. I got hold of an EVO 8 Front rotor and also a Subaru STI front rotor to test fit with some wheels. It turns out the Brembo callipers on the EVO's are the same as those on the STI Subaru's. The rotor's however are slightly different.
First the results for the EVO rotor. 320mm rotor with a thickness of 32mm. The "hat height" (or offset) of the rotor is 43.5mm (Standard S15 is 54mm) This means the rotor and therefore the calliper is around 10mm closer to the wheel spokes than stock. This was not a problem with the 17x9 stock R33 GTR wheels (offset +30), there was heaps of clearance, however, they still fouled on the Enkei RPf1's (offset +22). I guess it's true, the Enkei RPF1 is just not "Big Brake" friendly. The problem is the Enkei wheel is very cost effective and very light for it's size (around 7.2kg's for 17x9)
Next I tried the STI rotor. This is a 326mm rotor with a thickness of 30mm. To cater for the difference in rotor thickness, when you order STI Brembo pads, they are 1mm thicker than EVO ones. The "hat Height" or offset of these rotors is closer to the stock S15 rotor at 53mm. Obviously, they fitted the GTR wheels with no issue, the good news is, they also fit the Enkei RPF1! At Last, a combo that will fit!
So what does this all mean.........
On the down side, the thinner rotor means it wont deal with the heat quite as well as the EVO rotor, but should still do the job. The centre hole of the rotor is only 58mm, so it wont fit the S15 without machining the centre hole out to 68mm. There are not any "off the shelf" calliper adaptors in the market (that I know of) to bolt this set-up together, so I will need to get some made (if it's even possible).
On the up side, there are off the shelf 2 piece floating rotors available at very reasonable costs, the rotor is a slightly larger diameter (6mm) and the is also lighter than the EVO 2 piece rotors by nearly 1kg, in fact the STI rotor is only 300g heavier than the stock rotor. Which means, the combined weight of the rotor & calliper is actually 200g lighter than the stock combo while being 46mm bigger in diameter!
So the next step is to get the STI rotors centre hole machined to 68mm to fit the S15 hubs. Once that's done, we can start on designing the calliper adaptors to bolt the whole lot together!