DeerHunter

I know you're not keen on Carbotech pads, but the XP12 and XP24 both have incredible cold bite and will take between 1,850 and 2,000F. The only downside, for street use, is that they will squeal like a stuck pig. They also dust, but it's not particularly corrosive and will wash off easily.

OGRacing

iTrader: (1)

you asked for a two rig / street. didn't think you wanted a full race pad. a race pad needs to get around 200* to start producing MU. a PFC .10 street pads will produce Tq under 100*, they are just not allot. FYI 100* in a braking system is early in the morning pulling out of the garage. 2000* is 800* away from turning the rotor into a liquid. i haven't seen xp12's dyno but i have seen them fall apart at lower temperatures then 2000* . generally the highest you want to see a rotor operate at is >1600*

DeerHunter

Makes sense. I've never placed much stock in peak pad temps for the reasons you mention (plus the fluid would have boiled long before). I'm just saying that the Carbotechs do work well when cold (and it does get cold here, even in the summer). I mean, lock up your seatbelt retractor well, even with a medium brake application. I've experienced race pads that really don't work when cold and you generally sail through the first stop sign you come to in the morning. Just a data point for those that are interested.

I have to replace my front friction rings this winter and have to make a decision whether to go with the same (DBA 11" from Goodwin) or upgrade to the 11.75" kit (which necessitates new wheels for the street). Thoughts?

OGRacing

iTrader: (1)

if you got the money why not get the 11.75. they will last longer, rotors are easier to find/less expensive. with a wilwood prop valve we can get even brake performance with good-wins rear kit. but if you dont have the cash to upgrade stick with the 11"

Landrew

iTrader: (2)

I might give the PFC Carbon Metallic a go on a minivan (all I could find for my application) when I head to the US during Christmas break - thanks again

OGRacing

iTrader: (1)

#race-van

BrakePower

OGRacing, thanks for putting tons of great information out there.

I noticed that Leafy (page 4), like many others, struggled with the difference between a tandem master cylinder and a dual master cylinder set-up, regarding hydraulic pressure behind the M/C pistons. Explaining this, I always use the following experiment description:

Imagine two postal scales next to each other, bridged by a small plank. Reset both scales to zero. Place 10 lbs centered on the “bridge”, so both scales carry half off the weight and now read 5 lbs each.

Start over and place one scale on top of the other and reset displays to zero. Place the 10 lbs weight on the top scale... both displays now read 10 lbs.

In this experiment, the weight symbolizes the force coming from the push rod attached to the pedal assembly (driver input x pedal ratio). The two scales on top of each other resemble a tandem M/C and the two scales next to each other a dual M/C set-up with the “bridge” as balance bar.

I hope this explains why both pistons in a tandem M/C receive twice as much force from the brake pedal as both pistons in a dual M/C system with the balance bar at 50/50 (F/R) and everything else being equal.

Find more on M/C set-ups at my site (Cyotani already found it) on page: Tandem Master Cylinder | Dual Master Cylinder | BRAKE POWER

Closely related but not yet discussed, is pedal ratio. Because it is responsible for multiplying the drivers input (force on brake pedal pad), it plays an important role in the resulting brake torque at the wheels. More about this can be found here: Pedal Assist Ratio | Automotive Brake System Calculator | BRAKE POWER


Johnny, thanks again for sharing your knowledge and experience with us, making this a very interesting and educational thread for all motor sports enthusiasts.

glade

iTrader: (2)

Just saying thanks for the great info!

OGRacing

iTrader: (1)

I'm going to send your tables over to The PFC engineers. if it checks out this would be a good on line resource. All of mine brake calculators are pdf's :(

sixshooter

iTrader: (12)

I love this bar.

The exchange and discussion of ideas and information here is pretty cool.

hector

Lots of good info on this thread. Thanks for taking the time.

Now for an ignorant *** question:

What difference should I expect from going down to a 11/16" tandem master cylinder from a 3/4" tandem master cylinder as far as feel? Both are non-boosted.

We just recently deleted the brake booster from the car. Went from the 15/16" tandem master to a 3/4" tandem master. Awesome while autoxing. I could not believe how easy it was to get the exact amount of braking I needed from the car. With the booster it was always a crap shoot on initial pedal effort and if trying to modulate was even trickier. Only felt lockup a couple times w/o the booster and getting rid of it was easy w/o losing too much in brake force.

However, street driving was tough. Yes, I street drive a fairly well built CSP car. Not smart but neither is building a CSP car. We changed to an 11/16" tandem master and pedal feels much better for the street. I now find it easier to lock up the brakes with the softer pedal on the street tires which are bfg rivals. On A6's and with attack mentality Im sure it will be a different story.

Im going to find out in two weeks just what impact I made on what I thought to be an ideal setup as we have an autox coming up (Florida) but I just wanted to get your expert opinion on what to expect.

What I can remember about the setup:
Stock pedal ratio which I believe to be 4:1
Stock non-sport NA8 front brakes
Stock NA6 rear brakes
Stock NA8 proportioning valve
Front pads? I think Carbotech but compound is very soft
Rear pads? I think we are using the pads that came with the loaded calipers.
SS braided hoses.
Fresh fluid, nothing fancy.

I know our pad choices are suspect but the balance is good even with the stock prop valve in place and the bite for autox is good too. We used to run an aggressive rear pad on the NA8 rear brakes when we had them to tame the front bias but decided to wait and see when we switched to the NA6 rear brakes. It didn't do anything worse so we left it alone.

Obviously we plan to get rid of the stock prop valve and do correct pads for autox in the future but we are waiting to bet the FM LBBK for that.

Well maybe then I have two ignorant *** questions: what would you recommend for pads on the future setup?

OGRacing

iTrader: (1)

your madd! it's awesome seeing the initiative but your set up is all over the place with different components. i do spot some changes you should make that will help.

with a smaller master cylinder your going to get an increase in Fluid pressure, and a increase in pedal Travel. you might see the 11/16(.6875)" mc pedal go to the floor during a race. i'm not 100% sure that will happen but it is a possibility. When your at peak braking Do note where your foot is located. remember your peddle assembly has a sweet spot and starts to loose efficiency if the peddle travels past 90*.
Good news
your pedal ratio. Is still set up for a power system. 4:1 is far too short. ideally for a Manual system you'll want between a 5.2 - 5.7:1 ratio. This alone could make up for some lack in street TQ. with increased pedal ratio the 3/4" might be perfect. Drill a hole lower on the pedal and locate the master cylinder lower too. don't drill a hole .5" lower and jam the MC arm into it. the side load will dramatically shorten the master cylinders life.

As far as the Components your using I would look into upgrading the Rear NA6 brakes you have. When auto-crossing the Front tires have a huge load on them. Quick hands are not good for tire cohesion. i compensate for this with an above average rear brake bias. We do this because when your releasing the brakes and starting your turn, your Front tires have a lower duty on them and can begin the job of turning the car, while the rears are still doing some braking and helping rotate the car. look into some NA8 rear brakes or the 949 sport rotor kit.

Get rid of that Factory prop vale. The harder you press the less fluid gets sent to the rear. i hate those things.

Pads. I personally autocross on the PFC 01 compound. I do this for 2 reasons. 1.) if the transfer layer is there the Brake tq is very consistent. there is no Tq rise with heat. normally street driving will remove all transfer layer. so when you get to an event, it's gone. to get the transferlayer back, when you show up to an auto cross head over to the parking lot not being used, Accelerate up to 45 and drag the pedal down to about 10 mph. do this twice and your transfer-layer will come back. 2.) it's my track car and i don't feel like swapping pads. if your car is more of a double duty go with the HP+ pads the TQ increases with heat and that can be annoying, but the operating temperature does accommodate street driving.

sixshooter

iTrader: (12)

In your third sentence I believe you may have meant increased pedal travel and not decreased.

OGRacing

iTrader: (1)

yep your right, fixed, thank you!

hector

Yeah, I'm sure you were thinking WTF? when you were reading the ignorant **** we did. I'm surprised it turned out a working brake system. Although you have to really use some pedal pressure, it really was an improvement in feel.

It ended up the way it is as we were making changes to the car for getting rid of weight and we ended up using some flawed reasoning. Basically it was "make one change at a time" so as to know how one thing affected the brake system. The prop valve is just stupid, we should of gotten rid of it long ago, but we started making changes before turning our attention to it and then flawed reasoning kicked in. It is on the way out though, or so my co-driver said.

As far as trail braking, well neither of us is good enough for consistently doing that and not ending up in a spin so we try to do all our braking in a straight line. And what we are trying to do is use the brakes as little as possible anyhow as we both are overbraking too much since a miata is a momentum car and all that.

Oh and the pedal ratio. We cant drill a hole on the pedal but we can make a bracket to raise the pedal ratio a bit. We can go up on the pedal by about a half inch only since we can't cut the firewall and the outer bore of the master cylinder would interfere. This would give us about 4.8:1 pedal ratio.

Just so I know I'm doing the math right on the pedal ratio. The pivot point to the center of the pedal is 12". The pivot point to the master cylinder is 3". That's 4:1 correct? So reducing the length to the master by about 1/2" should work out to 12"/2.5"=4.8:1 correct?

So in your opinion it would be better to have the larger bore with better pedal ratio than the smaller bore?

Again, thanks for taking the time to answer.

OGRacing

iTrader: (1)

It would be better to have a pedal that doesn't travel past the 90* plane. i'm wondering with a smaller MC that your increased pedal travel will be too far forward.

Mishift

Are big brake kits worth it?

sixshooter

iTrader: (12)

Everybody hold on. Somebody's about to die in a fire.

OGRacing

iTrader: (1)

Get yo` Fire suits here! Get cha` Fire suits!! Suits | Driver

sixshooter

iTrader: (12)

Nice product placement and good segway! +1