Phantom got my gears turning...

[JMortensen]

All this talk about Phantom's setup got me thinking about my new brake setup again, and a problem I haven't resolved.

 

I currently have a set of Wilwood Superlite calipers for the front

with 1.75" pistons, and I have a set of smaller Dynalite 4 pistons for

the back, also 1.75" pistons. Front and back will both be run on 12.2"

rotors, 1.2" thick in front and .81" in back. I know that usually

people buy 1.75" pistons for the front and 1.38" pistons for the back

in Zs, but I already have these, so if they can be made to work that's

what I'd prefer to do.

 

I run on 10" slicks, and the suspension is not sorted to full F Prepared

level, but it should be capable of some pretty serious braking. I

think that stock Z's pull about .9g under braking (that's what I seem

to remember from an OLD Car and Driver). I'm guessing maybe 1.4 or

1.5g's for my car. That's a SWAG, so I might be WAY off, I just don't

know. I am not entirely sure how I would figure it out without being

able to drive it. Any suggestions on how to get an accurate number for

this variable?

 

Anyway I'm trying to use Tom's spreadsheet. Here it is for anyone who

doesn't have it already: http://sth2.com/Z-car/Brakemath.xls I think

that I figured out that if I run .75" master in front and 1.125" in

rear, that according to the spreadsheet that gives me 1.2 G's. Then I

was planning on running a proportioning valve in the rear line as well

because I already have it, and Cary said that he runs both the balance

bar and the prop valve on his setup. Since as Tom pointed out they are

not linear, I figure that Cary is running it to stay closer to the

correct balance over a greater range of braking effort.

 

So I guess the questions are:

Do I need to replace the rear calipers?

If I use these small and large masters, does that cause any problems

since one will move so much further when I step on the brake? How much

misalignment can dual masters take?

Anyone think I hosed the spreadsheet and should be running other size

master cylinders?

Right now weight is 50/50, total of 2530 (will probably be

significantly less when I'm done with all this crap I'm doing).

[tube80z]

according to the spreadsheet that gives me 1.2 G's. Then I

was planning on running a proportioning valve in the rear line as well

because I already have it' date=' and Cary said that he runs both the balance

bar and the prop valve on his setup. Since as Tom pointed out they are

not linear, I figure that Cary is running it to stay closer to the

correct balance over a greater range of braking effort.[/quote']

 

I do this to get more rear brake at first and as weight transfers I don't end up locking the rear. So as you mention to keep things balanced longer. It took a bit of time to figure out.

 

My braking numbers are very close to what you listed Jon. My car used to struggle to get to 1 g under braking even though it could turn in the 1.4 to 1.5 range. Under hard braking I now see g forces in this large.

 

So I guess the questions are:

Do I need to replace the rear calipers?

If I use these small and large masters, does that cause any problems

since one will move so much further when I step on the brake? How much

misalignment can dual masters take?

 

I don't think you need to replace the rears. The balance bar should be setup so that when you press it all the way and have pressure on the cylinders it is straight across. At rest they will typically sit at an angle when you have different cylinders. They can handle a large range of adjustment. I prefer to run a slightly larger master and have less pedal movement.

 

I ran the numbers you listed and I came up with needing 3/4 front and a 1 inch rear to get a range of .51 to 1.43 gs (and used the numbers of .58 for front mu and .4 for rear) With a proportioning valve I think this would work. I have a friend with a 510 than ran this same setup and it worked for him. He just used smaller MCs to have less pedal effort.

 

You can also use different pad materials in back to help out. I run the PFC 01 material for my car. You might consider one of the aggressive fronts with a medium torque rear, like the 97 compound. Or what ever your favorite brand of brake pad is.

 

Cary

[JMortensen]

My braking numbers are very close to what you listed Jon. My car used to struggle to get to 1 g under braking even though it could turn in the 1.4 to 1.5 range. Under hard braking I now see g forces in this large.

I think I am in the same boat you were in. I could brake hard in my Z before, but the problem was always that the fluid would boil within a couple laps time. So I'd be waiting for the tires to warm up for a lap or two, then I'd get one or two laps of good braking, then the fluid would boil and I'd have to back way off. I know my car should be capable of a lot more braking than it had before with the old brakes. Can't wait to flat spot some tires while I'm figuring it out.

 

Thanks for all the help Cary. If you wouldn't mind I'd love to know what size masters your 510 buddy is running. I would prefer a softer pedal effort, but I don't want the pedal hitting the floor, and Tom's spreadsheet doesn't really account for pedal throw, just the ratio between the two.

 

Also, when you say you ran the numbers and came up with 57% and 43%, where are you getting that from? I tried to make all of the specs as close to correct as I could, and I got this for Brake Torque Distribution:

 

Min Nominal Max

Front 55% 68% 79%

Rear 45% 32% 21%

G force .23 .76 1.2

 

Are those the numbers that you're looking at?

[tube80z]

Also' date=' when you say you ran the numbers and came up with 57% and 43%, where are you getting that from? I tried to make all of the specs as close to correct as I could, and I got this for Brake Torque Distribution:

 

Min Nominal Max

Front 55% 68% 79%

Rear 45% 32% 21%

G force .23 .76 1.2

 

Are those the numbers that you're looking at?[/quote']

 

I made about ten edits before I got that one right. I managed to keep screwing up the numbers in Tom's spreadsheet. I think you may have read one of the intermediate posts where I had your calipers as a 2 piston in the back. I was playing with my numbers too and forgot to put yours back in.

 

5/8 front 7/8 rear (my friends setup)

Operational G-Force Range >>> 0.61 1.10 1.49

 

His pedal travel was a little long for me.

 

3/4 front and 1 inch rear

Operational G-Force Range >>> 0.51 1.02 1.43

 

Front pads at .58 mu (I think this is the PFC 01 mu)

Rear pads at .4 mu (I think this is the PFC 97 mu)

 

You'd want to check the mu numbers to what you are using to make sure the range looks good.

 

Hopefully this makes sense,

 

Cary