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!

[Vince@Meanstreets]

pretty sure you'll get an answer as soon as the Migraine meds kick in.

We run .875's on the C5 C6 and wilwood 6 piston stuff with great feel.

[Blown353]

Nah, no migraine from the numbers... I run a lot more complicated numbers at work every day. What *will* give me a migraine however is constantly thinking about the various options trying to make the best decision to only buy things once.

I tried a 7/8 bore MC with my current C6/C4 setup years ago when I first put it on... pedal feel was OK but the amount of pressure required to stop the car quickly with street friendly pads was excessive so I went hydroboost. That easily fixed the effort issue but required a lot more "stuff" under the hood.

Now with even more extra "stuff" under the hood from the turbos and with the hydroboost pushing the master too close to the wastegate for comfort I want to go back to manual for simplicity and room. A reasonable pedal effort even though the brakes are manual would be nice too-- and I know that can be achieved with correct component selection.

Still scratching my head on the dual MC with balance bar vs tandem master cylinder arrangement and the best rear caliper selection...

[Apogee]

I'm pretty sure you're not calculating the dual MC/balance bar setups correctly, as the input force into each MC is divided in half assuming a centered balance bar. A tandem 7/8" bore MC and (2) 7/8" bore MC's in a balance bar arrangement are not equivalent, as the piston in the tandem unit are in series whereas the MC's in the balance bar arrangement are in parallel to one another.

That said, I like the C5/C6 brakes (or Wilwood equivalents with respect to piston area/rotor diameter/etc) in a manual configuration with a 7/8" bore MC and "GG" friction rated pads. While many may not consider "GG" pads to be street friendly for dust/noise/wear reasons, they're the best solution IMHO when seeking a simple, low cost and highly effective manual braking solution.

Tobin
KORE3

[Blown353]

Tobin,

The spreadsheet I'm using does support both balance bar & tandem MC applications. The numbers it returns are nearly identical to Ron's spreadsheets when I checked it by inputting the same piston sizes & MC diameters that Ron has run for others in the past-- I'm only seeing a very small (<2%) deviation between my numbers and his numbers. The reason for the slight deviation is because the spreadsheet I have only supports a single CoF for both front and rear pads while Ron's has separate front & rear CoF inputs to account for the temperature differences. I still need to update my spreadsheet to account for separate front and rear CoF differences.

I could be wrong though, which is why I asked for a double-check on the numbers.

My current C6/C4 setup with no prop valve has a 69/31 torque split (which is good.) However, assuming street friendly pads with about a .43 CoF, a .875 OEM style tandem MC, and 100# of pedal input that's only about 1250# of brake torque... not very good at all, and that was my impression when I tried to run them in a manual setup. More aggressive pads would help but as you said that comes with a dust/noise/rotor life penalty. The hydroboost made them really work well though... wish I had taken some line pressure measurements when the car was still running to see just how much force the hydroboost was providing.

[Hydratech®]

Gokou - you DO know that your current discussion is reading to me as if saying "I would like to remove my power adder / supercharger from my engine and go back to running naturally aspirated and still make 1200 horse" - right? It can be done, but the trade offs are enormous. You have been running a Hydratech hydraulic brake assist system since 2003. 12 years later, you are wanting to taste braking in manual mode again because of an exhaust pipe?

Making more power than ever with your current twin turbo LS build will definitely thrill you with the "GO" pedal with your new twin whistler's, but "rotsa ruck" finding happiness in matching a higher rear wheel HP level to what you have been used to in the braking department.

Some exhaust pipe routing is taking you back to manual brakes again? You may have forgotten what alternate braking options feel like twelve years later - here comes your refresher course in why you went with Hydratech so many years ago (when you where running your earlier centrifugal supercharged configuration).

Sounds like: "I can't fit my turbo downpipe where I want it to go, so I'm switching back to manual steering".

I say this most definitely not to make a new sale (as you have already been tickled with your existing system since '03, and have been a great advocate since), much more so because we see this day after day / year after year and observe how the story ends all the time. A "silly" exhaust pipe routing clearance issue now has you wanting to go back to manual brakes? All these years later of running a Hydratech system, you have forgotten and now need a "relearning curve"... Go back to the DOJO and take your hits.

Did I just toss a rock at a beehive?