Help with configuring a Wilwood manual setup

[Blown353]

Have a brake setup question.

Right now my car is setup with 13" C6 front / 12" C4 rear PBR calieprs and a Hydroboost. 5 years ago when the car was still running it worked well… but now that I’ve switched to the LS2 and turbos the master cylinder is really close to the exhaust manifold and wastegate. Also, things under the hood are now tighter on space to locate a remote reservoir with air separator for the power steering plus all the hydroboost hoses and the Lee filter I used to run.

I'd like to change over to manual brakes for simplicity and to keep the master as far away as possible from the exhaust manifold and wastegate. While I’d love to be able to slap on a smaller bore master cylinder with my current brakes and go I know from testing it in the past that the PBR brakes and their small piston areas don't play all that nice in a manual setup. By the time you put on a small enough bore master to generate enough pressure to make them work the pedal stroke is really, really long… and they still don’t work all that well.

Thanks to all the spreadsheets Ron has been posting I've been running a lot of numbers. While I was thinking about sticking with a stock-style tandem master I've also found that CNC brakes makes a dual master cylinder with balance bar arrangement that will bolt to a GM firewall which opens the doors to a lot of options.

All these numbers assume 13” front and rear rotors-- if Wilwood could set me up with 13 x 1.25” front and rear rotors that would be great, but it looks like for some of these setups only 14” rotors are available.

For a stout manual setup, it looks like The Aero 6's up front are the hot ticket. I can’t argue with the numbers, lots of piston area.

Wilwood Aero 6 calipers up front with 1.75 / 1.375 / 1.375 pistons

For the rear, I see a couple of options. If I were to use a stock style 0.875 tandem master cylinder and use BP-10 pads at all 4 corners on the street, these calipers would provide the following front to rear brake force ratios and total torque with 100# of pedal input @ 6.25:1 ratio.

Wilwood Aero 4 with 1.125 / 1.125 pistons: 73/27 split, 3200 torque

Wilwood FNSL4R with 1.25 / 1.25 pistons: 68/32 split, 3400 torque

Wilwood FNSL4R with 1.375 / 1.375 pistons: 64/36 split, 3620 torque

If I run a stock style tandem master cylinder with a proportioning valve for the back brakes I'd choose the FNSL4R calipers with the 1.375 pistons. Since you can only decrease the braking force on the rear with a proportioning valve that should allow me to tune the back brake bias down to around 70/30 or whatever the car likes given the final tire selection and weight distribution. Since the car is primarily a street car maybe going with a stock-style tandem master and a rear proportioning valve would be simplest solution.

However, with the CNC dual master and balance bar arrangement any of the options could be made to work… I see the following options for the rear calipers & master bore setups.

1. Aero 4 1.125 pistons with a .875 front and .875 rear master. With the balance bar centered that would be a 73/27 torque split, adjusted for a 70/30 split that’s about 3100 torque for 100# pedal input.

2. Aero 4 1.125 pistons with a .875 front master and .750 rear master. With the balance bar centered that would be a 66/34 torque split, adjusted for a 70/30 split that’s about 3620 torque for 100# pedal input.

3. FNSL4R 1.25 pistons with .875 front and rear masters. With the balance bar centered that would be a 68/32 split. Should only take minor balance bar tweaking to get to 70/30, and adjusted to 70/30 100# pedal input produces about 3440 torque.

4. FNSL4R 1.375 pistons with .875 front and 1.0 rear master. That yields a 70/30 torque split with the balance bar centered and will produce about 3320 torque with 100# pedal input.

5. FNSL4R 1.375 pistons with .875 front and .875 rear master. That yields 64/36 torque split with the balance bar centered. With the balance bar adjusted for 70/30 it will produce about 3760 torque with 100# pedal input.

Thoughts? I know the FNSL4R calipers have a price advantage over the Aero 4s, but it will only be about $450 price difference for the pair. I'm sort of leaning towards setup #2 or #5 if I go with the twin masters and balance bar but I'd really appreciate some input. I'm also torn between a stock style tandem master & prop valve vs a dual master and balance bar on what is primarily a street car. Thanks!