Balance the Rear brakes - FD with front BBK
 

So I have a wilwood BBK on the front of the car.

I know, overkill (most of the time) heavy for autox, but that is what I have, and not currently interested in changing it.

There is no ABS, and even with the proportioning valve set to 85% or so for rear pressure, the fronts are still too easy to lock up.

This only got worse with a move to 335/30/18 on the rear.

Does someone here have experience with using a 99 RS rear brake setup to balance this out a bit?

That is about a .5 inch diameter increase over 93 stock size as I recall, and am wondering if that is enough?

Or would the Sake Bomb Garage rear brake setup be a better way to go?

Fd need much more rear brake bias then factory design
This is what I do on my road race car
Front is stock.99 spec caliper
With much larger rear rotor 325mm rear
And rear I use,more agressive brake compund then front

Here are my corner weight
As u can see , with mine 53%rear weight brake bias, we need a lot more rear brake
I start up with 99, but I just feel rear brake bias just not enough, so I keep adjust it
Until I feel is at right diection

Thanks diyman25, the info is much appreciated.

I'm running the Racing Brake BBK front and rear. They are the ones that added a larger rear disc and spaced out the stock caliper with a new bracket - which is what I think SB is doing now. Before this I was running front and rear 99 spec brakes. The additional mechanical leverage of the bigger rear disc and spaced out caliper make a big, welcome difference to brake bias. On track, the car is more steady balanced and controllable under hard braking. I think I used the same compounds front and rear with this setup iirc.

This was with stock ABS fwiw

I have a set of new rz rear rotors if you decide to go that route . They are 12.36 x.79 or 314x20.

I was running huge 14x1.4 rotors with Brembo gtr monoblock 4 piston fronts, with a hybrid supra turbo front rotor in the rear with a corvette c5 rear caliper which is 45 mm piston vs 30mm rx7 . This worked really well until a 991 cup car showed up.

Over the winter I will be fitting the full 991 cup car front brakes and supra turbo rears with a nascar Brembo 4 piston rear caliper.

https://cimg3.ibsrv.net/gimg/www.rx7...f5bfd2563.jpeg
https://cimg2.ibsrv.net/gimg/www.rx7...e768d0e6d.jpeg
https://cimg4.ibsrv.net/gimg/www.rx7...957091a4d.jpeg

https://cimg5.ibsrv.net/gimg/www.rx7...0e75dca31.jpeg
https://cimg6.ibsrv.net/gimg/www.rx7...5d6d7290b.jpeg

Nice set up
Wonder how u calculate Master cylinder size

The rear sliding caliper on the FD is 35ish in the piston.

If there's no ABS, the definitive way to fix the existing set-up is a pedal box, either bought or made. I'm currently doing something similar to what Revolution over in Japan does. Severe doubts about the welded and modified stock pedal they do, so ditched that for a laser cut steel one bent to shape and improved the 4:1 ratio to 5.5.

You could improve things maybe a touch with a rear pad with less friction or something with a lot of bite up front at the cheaper end of modification. The 10mm increase on the radius with 17" brakes or 18mm with Sakebomb would hopefully improve matters further.