Hey boys, my FB time attack car is getting stock FC 4pots up front and T2 rear calipers.

I'm going to be ordering a floor mount triple pedal box soon and I'm kinda stuck on sizing the brake masters for the FC brake calipers.

Now, I may go with larger brakes later on in life....but I think the FC's brakes will be alright.

Give me your input.

Thanks

 

Well, I have Mazda 4pots up front, Wilwood 4 Pots out back am using TII boster/MC with a wilwood proportioning valve and the brakes are really good on the FB.

I would say to use a 1" or 1 1/6" if you are going to use a single cylinder or dual 3/4" for a twin piston mc type.

Others may have a different opinion.

 

6:1 pedal ratio
5/8" front
7/10" rear

tested, proven.

 

Well now thats what I call a straight forward answer....

Thanks!

 

Thinking out loud here because I am facing the same decision on my FB project.

Wouldn't using M/C's with the stock bore work? I would think that this would be fine because matched stock calipers are being used front and rear and the only variable that is changing is the ratio of the pedal to accomodate the lack of power assist.

In my experience with other dual M/C setups having the bores the same or only one size different makes the mechanical bias adjuster work better. I had a setup on a Mustang that had a 1" for rear brakes and a .75" for the fronts and it was hard get good bias and a decent pedal feel.

Next question.....what is the stock bore on an FC M/C with TurboII brakes?

 

not really that simple

S5 cars with ABS (which in the US was turboII cars for the most part) hat a 15/16" MC

all others had 7/8" (I am fairly sure)

 

When you get rid of the stock bias manifold thingy you really need a better way to control the line pressure to the rear calipers. A bias bar alone won't give you enough drop in rear pressures to keep the rears from locking under hard braking. IIRC the stock bias adjuster is able to cut up to 70% of the line pressure going to the rears.

You might be able to go to a more favorable pedal ratio and stay close to the stock master diameter but you will have a VERY hard pedal. Probably in the 120+lb range. A light pedal is 60-70lbs and the masters I listed give you a 85-95lb pedal.

I worked with Tilton on the combo and it has worked well.

 

Very cool - thank you!

 

Back from the dead.

Tiltons website doesnt specify the pedal ratio. Do they all just come with 6:1?

http://www.tiltonracing.com/content....list2&id=8&m=b

 

No, the stock pedal is closer to 5:1. There was no way to get a balanced set of masters using the stock ratio because you would have to go smaller than 5/8 for the fronts.

Most aftermarket pedals come in the 6:1 range, if you are buying new, that is what you need. A higher ratio will give you a pedal that needs less effort but you may run into pedal travel issues if the system all of a sudden goes "less than optimum"(brake fade...)

 

You, sir, are a smart man. Very glad to see good information. Manual brakes seem to be a lost science among most. I've only been messing with them for the last couple of years, but The biggest thing I normally see is people's lack of understanding that a smaller master cylinder creates more pressure and in turn have a larger MC for the front than the rear.

So a couple more things just for future searchers:

I own the book below and has helped me to develop a much clearer understanding of brakes in general.

A great book and resource for brakes and manual brakes: http://www.amazon.com/High-Performan.../dp/1932494324

From the book

Gain: Gain is nothing more than a fancy way of saying multiplication. The brake system gain relates the amount of brake system force input to the brake system force output.

Also from the book:
Overall Brake System Gain Cheat Sheet

System Parameter / For More Gain / For Less Gain
Brake Pedal Ratio /increase /decrease
Brake booster Gain /increase /decrease
Master cylinder piston diameter /decrease /increase
Caliper piston diameter /increase /decrease
Brake Pad coefficient of friction /increase /decrease
Rotor effective radius /increase /decrease
Tire rolling radius /decrease / increase

 

I'm a little confused and I think you mis-understood my question.

What I'm asking is; if the Tilton pedal setup come as a 6:1 ratio? They do not look adjustable.

I'm buying a Tilton pedal box #72-680 and will be using the Master cyl sizing you recommended above along with stock FC 4pot front calipers and stock FC T2/GXL rear calipers.


Also, would you happen to know if a 5/8" master would work well with the stock FC T2 slave cyl?

 

They use to come in at least a couple of different sizes and am sure they probably still do. The standard size that most people buy is 6.2:1. I believe you can also get most in 5.5:1. I think the majority of us are talking about an overhung/top mounted pedal assembly. I'm not too familiar with the floor mounted versions like the part number you have listed. Seems like it'd be difficult to fully ultilize the throw/leverage of the pedals. Lego has one in his FC race car(LS2), but I don't remember his username on here. Maybe Legoken?

You also may want to just give tilton technical support a call. They can help figure out exactly what you need. Clutch MC size for your slave cylinder, as well as your brake MC sizes.

 

Joe!

Just noticed this thread. Your building a Time Attack Car? Where are you running this? Come join us down at the Sigma Time Attack Series next year or the CASC sanctioned? Time Attack!

Ian

 

To clarify - the sizes you found to work are 5/8" (.625) and 7/8" (.875) OR 7/10" (.700)? I am getting ready order master cylinders and wanted to follow your lead.

 

Took me forever to find it, but the stock FC clutch slave cyl is 5/8".....well according to the FSM.

So heres what I'm getting;

Tilton pedal box
2 Wilwood 5/8" compact master cyl
1 Tilton 7/10" compact master cyl
Wilwood remote bias adjuster

Ian, yea I hope to have this car going this summer and out to a bunch of events, I have legit sponsors this season so I cant disapoint lol.

 

Oh and dang, I called Tilton and the pedal box I'm getting is 5.5:1 fixed ratio. Not ideal but I'll make it work lol.

 

You want the 7/10" with the 5/8" on the front. Gives a nice pedal, not too hard, not too easy.

 

The bias will be fine, you will just have a pedal the requires pretty high foot pressure. Find a bathroom scale and see if you can sit and push on it with one foot with about 130lbs, I'm thinking that it about what it will take with a 5.5:1 pedal.

 

Thanks!