Thanks for the answers guys. Maybe i need to go deeper into what I am doing so we are on the same page.
Basically I am building an entirely new brake setup consisting of:
- Porsche Boxster 986 4 piston monoblock calipers all round (They have different size calipers front caliper pistons - 40/36mm - rear caliper pistons - 30mm/28mm)
- 15/16th master cylinder (which is what the Porsche has)
- Custom braided lines (required to fit the calipers anyway)
- Obviously custom brackets to mount calipers
- 323mm 2 piece DBA front rotors 26mm thick (from an Rx-8 sport package - 47mm rotor offset - 8% increase in size)
- 260z hubs
- Handbrake caliper setup
- Willwood Line Pressure Reduction valve
At this stage, I was thinking of going S13 Silvia front rotors for the rear (easy to get in 2 piece 280mmx22mm) or Z31 front rotors. (274mm x 20mm - correct width for the caliper).
The Boxster comes factory with:
- F Disc 298mm x 26mm
- R Disc 292mm x 20mm
From what I have read, a rear engine car will have a more rearward brake bias from the factory than an front engined car. So what I am trying to do is have a more rearward bias than a factory zed to allow for fine tuning but at the same time run the smallest rotor I have to at the back for unsprung weight advantage.
Roberto's answer has been helpful for giving me a ball park to base my targets around at 70:30 and probably aim for 65:35 as a minimum. I think the Boxster is pretty close to 50:50 and obviously I need to figure this out too.
As Jason has suggested previously I can do this using % increases and decreases from the stock setup, but this becomes hard with drums at the back.
The other question i need to answer is will a caliper designed to work with a 292mm rotor work on something as small as 280mm as that might be another limiting factor?