Thanks for all the input guys! When I went to the track the first time I boiled the brake fluid and changed it from whatever the previous owner was using to Motul RBF 600 as recommended by a friend who uses it in his Evo which sees regular track time.
 
The car has Project Mu pads but I'm unsure which type as I didn't put them on the car, and I do still run into pad fade sometimes.
 
I'd thought of controlling the bias with an adjustable proportioning valve and moving the knee point as well as reducing the rate that the pressure drops to the rears from that point. I hadn't thought of trying different coefficient pads front vs rear, that's an interesting idea!
 
It does sounds like I'll be better of waiting till I have the rears sorted before installing the BBK's and just trying new pads for the time being.
 
Any suggestions on pad choice? They'd have to be appropriate for daily driving as well as track use so I wouldn't be able to use pads that take a while to reach operating temp.
 
I do remember Eric mentioning having his setup on a brake dyno, I'd never heard of one before, is it done on the car and can they be used to help you fine tune your setup?

5SGTE
Pretty sure Eric had his on the brake dyno.

Yes, I had mine on a brake dyno with the Delta V Kit front and rears. 

I cant remember the numbers, but the car was maxing out the brake dyno when the rear wheels were on it. 

The rears provided more force than the fronts in this situation, as the fronts would lock up due to the cars natural weight distribution. Talking to the brake shop, they explained that with mid engined cars, the rear brakes were very important in a good setup.

I would not run just a front BBK.

I just fitted a set of Delta V big brakes front and rear (supra front rotor / rx8 rear rotors). I haven't had a chance to take the car to a track yet with these brakes or bed the brake pads in however I did take the car for a drive around the block a few times to makes sure the fluid was bled properly and everything was working right. I find it very easy to lock front brakes with this set up. The rotors and pads are both new so hopefully when bedding in and at proper speed the balance comes back to the factory setup but as it is now the fronts lock very easily. The car is a Gen 3 with the factory master cylinder.

TonyMR2
http://www.mr2oc.com/59-g...-caliper-mc-sizes.html

A little info.... What I read into (love mr2 research), bias is factory set to release pressure on the rear when pressure exceeds the setting. A rear upgrade, such as a larger disc, does not change the piston or piston pressure managed by the bias. I can understand that not upgrading the rear (disc size to assist in heat dispersion or hot spots) would be a recipe for disaster if your pushing more "stress / demand" on the brakes.

Be interesting if anyone has had access to actual braking monitoring equipment that gives g and other data. Challenge is it is so dependant on brake pads used.

The rotor size does make a big difference for braking force. This is because bigger rotors mean the calipers get pushed further out and the further out they are the more torque they produce. The same deal as using a big wrench vs a smaller wrench. You need less force to get the same leverage. So in the case of fitting BIG 4/6 pistons brakes up front odds are the rotor will be bigger, giving greater torque, the pad area is bigger giving greater friction, however your still pushing the same amount of fluid through the brake lines for the same amount of pedal travel as before as you still have the same master cylinder however the pots are larger (more pots/larger in total) most likely then what the factory calipers had so this negates the pedal effort a little. (Confusing I know, so basically if you fit a really big set of calipers and keep the same size master cylinder, you have to push the pedal further down before the brakes work because you need to push more fluid to fill the pots). So ultimately if you fit big brake kits using after market calipers you CAN SOMETIMES end up with worse then factory brakes or lots of experimenting to get the right pedal feel and balance.

Lets not forget that there is no point doing a BBK if you aren't going to put sticky/wider tyres on. If you're already locking up average tyres with standard brakes, a big brake kit will not provide any improvement