Pedal Box, Selecting Correct Master Cylinders.

[32_Dave]

Hey guys,

trying to do the maths to select the correct master cylinders.

for clutch the master i have is a 5/8 and is paired with a standard slave 3/4.

Im struggling to work out the correct size required / with or without a nismo slave.

same for brakes front are currently using a BM44, now being a pedal box you need to remove the booster, so is it down a size or up?

front brakes are 4pot r33 gtst items rear are r32 gtst 2 pot systems. there is also an inline hydraulic handbrake i need to calculate the correct master size for i gather you choose the same for the rear brakes.

the pedal ratios available are:

5.29:1

5.44:1

5.61:1

5.75:1

Im terrible at maths and am struggling to work out the piston area, so i can convert to required PSI pressures.

information on brakes.

R33 GTST

Master Cylinder diam (mm) 23.8 444.88mm²

Front Caliper Piston(diam x qty) 40.4×4 = 5127.58mm²

Front rotors (diam x thk) 296×30

Rear Caliper Piston(diam x qty) 38.18×2 = 2289.78mm² ratio FR = 2.239

Rear Rotors (diam x thk) 297×18

Total area 7417.36mm²

Brake to master ratio 16.67

If anyone out there has the knowledge please help !!!

tar

Edited June 29, 2011 by 32_Dave

[32_Dave]

forgot to add there is a good conversions table here: CLICK

[32_Dave]

here is my workings for the clutch to start with.

5/8 = 0.30 "2

@ stock pedal ratio of 4:1

at 100 pound force 400/0.30 = 1333 psi, so correct me if wrong the stock setup exerts 1333psi to the slave cylinder?

so when you change the pedal ratios you get.

5.29 = 1763.33psi

5.44 = 1813.33psi

5.61 = 1870.00psi

5.75 = 1916.66psi

does this mean you then go up a size in master cylinder as you only are required 1333psi, which will result in a easier to de-press pedal?

so say you go to the next size on the highest pedal ratio.

0.75" master being 0.44 "2

at 5.75:1 ratio you get 1306 psi, would that have lighter pedal but not enough pressure?

am i on the right track or totally way off.?

[Tektrader69]

Dave, suggest you send an enquiry to Tilton.

I cant fnd the link now BUT when I was trying to work this out they had an online form with a long list of parameters for your car. They then replied with suggested master sizes.

Was very helpful, Then I went and totally changed my brake setup which made my masters I had already bought, very very wrong.

Edited June 29, 2011 by Tektrader69

[Risking]

Your over comicating the whole thing.

5/8ths for the clutch nothing else.

What brand of pedal box are you considering?

If you've never done it before get something with a 6.25:1 ratio. Tilton do the best around.

Any idea what the car weight is and a rough % split?

Tire type and size?

With that I can give you a decent starting point

[32_Dave]

Your over comicating the whole thing.

5/8ths for the clutch nothing else.

What brand of pedal box are you considering?

If you've never done it before get something with a 6.25:1 ratio. Tilton do the best around.

Any idea what the car weight is and a rough % split?

Tire type and size?

With that I can give you a decent starting point

yeh i do tend to read into shit to much.

looking at a tilton box either a 72-680 or 72-603

car weight would be high 1100's to low 1200's

what you mean %split weight ratio?

tires change all the time wheels are 17x9.5 but may end up going 18x9.5 and 18x10 or 12

thanks mate,

ps: what ever happen to the carbon door card group buy?

[Risking]

If you go with a 72-680 you will want the throttle linkage to go with it.

I have one of those pedal boxes here for stock with a throttle linkage. Really nice bit of gear

% of the weight split front to rear.

The 72-603 is obviously only a twin pedal design. Also a really nice unit I have two of those currently, only problem using one of those in a skyline is the need to fabricate a custom throttle pedal to get a nice pedal position with the brake and clutch pivots being off the floor instead of overhung.

Much easier to Get working than the 3 pedal types with custom throttle cables and brackets etc

If your serious about setting up a pedal box id recommend working out the rest of the car then making the pedal ratio and master selection.

I'm still doing those carbon trims but a group buy was a pain in the arse so never went ahead.

[32_Dave]

i need to get the car corner weighted to find the % split and don't have the resources atm.

rb25 mounted about 180-200mm into firewall stripped interior + cage fuel cell

[Risking]

I'll do it today for you working on a theoretical 50/50 with a 5.5 ratio pedal.

The 603 is actually a twin pedal alloy box too sorry I was thinking of the 604 which is a two pedal.

[32_Dave]

thanks mate.

[32_Dave]

I'll do it today for you working on a theoretical 50/50 with a 5.5 ratio pedal.

The 603 is actually a twin pedal alloy box too sorry I was thinking of the 604 which is a two pedal.

hey man,

how did u go? no reply to pm etc?

anyone can help would be great tar.

[Risking]

Sorry been busy, this wasn't a priority.

If I get time tomorrow I've got another set of masters to work out so I'll do it then.

[32_Dave]

your right man, didnt realise u were going so hard out on it, take yo time.

thanks

[savant]

Might help a little, on our R32 GTR with standard GTR brakes (so slightly larger pistons) we run a 5/8" front and 3/4" rear. This is with a Wilwood 6.25:1 pedal box. The car is a bit heavier than yours. We guessed to start and used 3/4" front and 7/8" rear which was too hard, but the smaller ones work really well. Have saved the bigger size for when we upgrade the brakes.

Cheers

[32_Dave]

thanks savant.

would like to get all this sorted asap as need to order this gear asap.

peace

[Risking]

With a 5.5:1 pedal ratio theoretical master sizing with a 50/50 split in weight

I'd be starting with a 5/8ths front and a 7/8ths rear

The rear may be a touch on the large (firm) side. If that's so it won't be using the rears as much as the fronts

You can tune that a little with the balance bar but if it's still not getting good rear bias you can use a different pad compound to compensate.

That combination will give you a fairly firm pedal with a shortish stroke and good pedal feedback.

Same masters with a 6.25 pedal will increase the stroke and lighten the pedal up a touch.

I'd do 6.25 if it's your first pedal box

Makes it easier to find that fine line of locking fronts and is easier to learn threshold braking without assistance.

Much more forgiving if your masters are slightly wrong due to the increased leverage.

[32_Dave]

thank you risking very much, did u find my PM regards your pedal box for sale?

[32_Dave]

has anyone had to do with hydraulic release throw out bearings?