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Alright now I'm going to compile the data on a complete front and rear Wilwood system for a 15" wheel, and than I will work backwards from there for others that have 14" wheels. I have purchased the parts for the front and I am currently waiting for the rest of the parts to arrive. Once I successfully install the front I will move onto the rear Wilwood components. I started this on Geometroforum, but want to condense this onto a location more dedicated to the GT(i). This is not a cheap part list so be prepared to spend some money for those that want to follow. I started by gathering data from Redlinegti and Teamswift, and realized there was ton of unanswered questions. Hopefully, by the time I am done with this thread the upgrade to a Wilwood system will be easier to do and you will have answers to those unanswered questions.

PARTS LIST FRONT : I recommend SummitRacing for most of the parts.
1. Two Billet Dynapro Radial Mount Calipers WIL-120-7380 (1.75 square inch pistons) (you can choose piston size and color)
2. Brake Pads Smart Pad BP-10 for Medium Friction Street use WIL-150-8946K.
3. Brake Rotors 11.75" left WIL-160-7102BK, right WIL-160-7101BK; these are not the only option.
4. Two Rotor Hats WIL-171-7671 8x7.00, .73 hat offset; again these are not the only option.
5. Two EAR-916104ERL Brake Line Fittings.
6. Two FRA-6500225 Brake Line Fittings.
7. Hardware listed below.
8. Machine hats center bore to 64.1 mm, drill 4x4.5 bolt pattern (1/2" diameter), drill and counter sink mount screw holes ( helpful to bring a stock rotor with to match).
9. Dxf files for front and top view of front brake bracket. DISCLAIMER THESE FILES ARE FREE TO VIEW AND USE AT YOUR OWN RISK! These files are intended for view only, and creator of said files will not be held accountable or liable for production and safety of said production.
Front dxf file: I'll link these as soon as I cut one more set from the updated bracket
Top dxf file:
Part measurement file:
Freecad file: You can down load Freecad and mess with the file yourself. It is free.
10.. Machine brackets minimum of 2 hours worth of work even with printouts and dxf files.
11. Anodize brackets.
12. Brake Fluid.

Lets's start by posting some resources that I read and referred to for the math involved:
https://www.joesracing.com/rt-4172-mast ... -math.html

http://www.stoptech.com/technical-suppo ... ce-matters

http://www.engineeringinspiration.co.uk ... s.html#top

Next I want to identify some of the stock GT(i) parts for a comparison between stock set up and the 11.75" rotor with Billet Dynapro calipers with my own custom bracket. I will later also try to compile the complete statistics on the Honda Brake Upgrade for comparison.

The stock front set up
master cylinder: 13/16-.8125

Master Cylinder Pressure:
The amount of pressure generated is a function of the force being applied, divided by the master cylinder bore area.
Convert bore diameter to bore area Area = 3.14 x radius squared (the .785 is a constant that makes the math more simple for all area calculations).

0.8125 x 0.8125 x 0.785 = 0.5182 inches squared

100 lbs of force from foot
100/.5182" = 193 psi
100/.7885" = 127.4 psi (a 1" master cylinder)
This means that a smaller master cylinder bore will result in more line pressure. A smaller bore will also result in less fluid movement

Our stock maser cylinder is an in line two piston set up. The piston closes to the firewall activates the right front and the left rear, and the other piston activates the left front and right rear. None of the calculations include the addition of the brake booster which applies equally to both pistons and therefore isn't all that relevant to the math. The force applied from foot to brake pedal leverage to pistons should apply equally to the two pistons where the force applied divides in half to the (right front,left rear) and (left front, right rear).

Technically speaking the following clamping force amounts would be altered do to the fact that master cylinder is providing for both front and rear brakes and there is proportioning valve. However, the numbers reflect accurate proportional ratios between different calipers. To get more accurate rear clamping force numbers I believe you would simply reduce the clamping force by the same percentage of pressure reduction. This is an unnecessary step since the proportioning valve will reduce all calipers equally, and the proportional ratios between calipers will remain the same.

Clamping Capability:
Is the ratio between net bore area of caliper (one side only) divided by bore area of master cylinder.

Stock front
1.892" x 1.892" x .785 = 2.810
2.810/0.518 = 5.425:1
Example with larger master cylinder 1"
2.810/0.785 = 3.58:1

Stock rear
1.181" x 1.181" x .785 = 1.095
1.095/0.518 = 2.114:1
Last edited by GT4LIFE on Tue Jul 17, 2018 12:03 pm, edited 8 times in total.
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By macuserman
I'll be following your thread closely. This is something I want to tackle myself at some point. I've got the honda front calipers on mine already and they do work pretty good so far.
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How about starting with some pictures of the front system. The front Wilwood system is complete and functional. The rear system is still underway, but I do have the mounts designed for it.

As you can see the calipers are way out there.

There is the recommend minimum clearance of .08 for everything. I had to shave the two inner outer edge of the pan bolts. It is only the edge that you see there that only has the .08 clearance everything else has considerably more as the wheels taper larger as they go in. There has been no interference with the setup at speed with high speed cornering.

This setup is using 15" wheels with a combined wheel offset of 35 mm with the bracket placed on the inside.

This is the front bracket. I designed this in Freecad and will be posting a Freecad file, and the top and front dxf files that can be brought to machinist with a cnc machine. Your machinist will need to make the CAM pathways and setup the Gcode for the machine. I still have a little bit of tweaking to do to the file before posting. The machinist will inevitably need to add a rectangle pathway that extends outside of the top cube cut to get a straight cut through the top inner cutout. There may be some overlap pathways in the inside mount radial corner cuts that will need to be cleaned up in the CAM setup. Before I'm done I will post up a 3D views with measurements which will be extremely helpful to have on hand and give to your machinist. The file will leave the Wilwood Dynapro Radial mount caliper centered on the disc without shims. This is of course if your using the same 11.75 discs and 8x7.00 with .73 hat offset. If you read further down I will post separate files to allow someone to use these Wilwood calipers with a 11" or 10.75" disc rotors using an alternate 6x6.25 171-8975 with a .77 hat offset.

If you want more clearance than posted above you can run the bracket flipped around and mount it to the inside of the stock brake mount flange and run the blots from the outside in. You would purchase the 1.22 offset hat 171-8976. You will also need to purchase some 12 mm or 1/2" inside diameter spacers by 3/8" thick to move the bracket in to align the studs with where the caliper would sit with the 1.22 hat offset (1.220.73= .49, but you will probably want to use shims listed above to bring it out from there to precisely center it.) The 3/8 shims listed above can be honed out with a dremel tool to fit 12 mm. You will probably need 12x1.25 x 40 mm long 10.9 bolts.

The bolts are 12 mm x 1.25 x 35mm. I bought 5 of these bolts off ebay. You cannot use anything wider flange diameter than these bolts as they will not fit. You could easily get away with using 30 mm bolts also. The bracket with bolts, studs, locker washers, shims, and nuts only ways 1.2lbs.
Things you will need with the brackets
1. four 3/8-16 by 3/8-24 double ended studs 675-007; the length I believe is 2 3/4" (I bought them at Ace Hardware).
2. four 3/8-24 Wilwood self-locking nut 230-9183 (ordered from Summitracing)
3. 2 packages of Wilwood's .375 shim washers 240-4384 10 in a package (ordered from Summitracing)
4. two sets, Rotor/Hat bolt kit 5/16-18 x 1" WIL 230-8390 set of 8 bolts
4. Red locktight
5. four 12 mm x 1.25 x 30 mm bolts 10.9 grade (Ebay Rivercity Fastners)
6. four 12 mm lockwashers (Ace Hardware) I bought stainless steel.

These are the 8x7.00 hats 171-7671 which come with blank faces and a .73 hat offset. You will have to have the holes drilled to 4x114.3 (4x4.5)(1/2" works for hole diameter), and the insider bore lathed to 64.1 mm ish. Wilwood does sell a 8x7.00 hat 170-6996 with a.73 offset that is drilled with a 4x4.5 hole pattern, but the center bore is larger than 64.1. This means you would be depending on the two screws to hold you discs in place, or you you be making a custom ring spacer which I don't recommend.
These are 10 mm wheels spacers. You will not need these if your wheels are already 35 mm offset. If you do need spacers I recommend Blox Sport on Ebay. They can custom make you any spacers. These spacers were already hub center 62.1 to 73.1 for a lexus. The spacers started as a 5x4.5 ten hole, which means you will only need to drill two additional holes. However, I had all the spaces drilled to lighten them up. If you need spacer you will need longer studs. I recommend switching to 12mm x 1.5 arp studs 100-7708. You will need to cut them down to length. You will then need to purchase a set of 12mm x 1.5 lugnuts.

The discs are directional: 160-7101BK and 160-7102BK. These ones are 11.75" or 298 mm and the width is .81". There are other options with the calipers I have selected. You will have to look through Wilwood's catalog.
Last edited by GT4LIFE on Sun Jul 15, 2018 2:14 pm, edited 11 times in total.
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Some Comparisons: STILL EDITING

Stock front:
rotor diameter 250 mm .81" width
brake pad area: 5.787 inches squared
Single piston floating caliper 1.892" bore diameter
1.892" x 1.892" x .785 = 2.810 inches squared of functional surface area
2.810/0.518 = 5.425:1 clamping force ratio

Stock rear:
Single piston floating caliper 1.181 bore diameter
1.181" x 1.181" x .785 = 1.095
1.095/0.518 = 2.114:1 clamping force ratio

Dynapro front:
rotor diameter: 298 mm one shown (variable in size) recommend using a .81" width
2 hat sizes that fit 89 to 94 GT(i): 6 x 6.25 171-8975 = 10.75 and 11" rotors 8 x 7.00 171-7671 = 11.75, 12.00 and 12.19" rotors
(There is a pre-drilled hat that is 4x4.5 but the bore diameter is too wide and cannot be machined to fit our bores exactly.)
brake pad area: 6.36 inches squared
4 piston fixed calipers (variable piston sizes; largest 4.8 inches squared; see other sizes below)
1.75 x 1.75 x .785 = 2.404 x2 = 4.808
4.808/0.518 = 9.282:1 clamping force ratio
5.425/9.282= the stock clamping force is only 58.4% of the dynapro calipers clamping force. Flipped: 9.282-5.425 =3.857/5.425= 71.1% greater, or 1.711 times the stock clamping force.
250/298.45= the stock rotor is 83.8% of the larger rotor. increase in rotor diameter. 298.45-250= 48.45/250= .194 or 19.4% greater, or 1.194 times the stock rotor diameter. This will increase torque stopping force.
Remember that changing to a radial mount 4 piston fixed caliper (balanced on either side) will all help braking performance.
Additionally, this setup will give you access to 10 different coefficients of brake pads, and the pads are larger.
5.787/6.36= the stock pads are 91% of the larger pads surface area. 6.36-5.787= .573/ 5.787= .099 or 9.9% larger. The pad installation and removal is the easiest I have ever seen and used. All this comes with much higher price.

Honda front:

I did some searching and it looks like the Honda Crx Si caliper is different between 88-89:50.8 mm or 2" and 90-91: 53 mm or 2.09". The Honda are float calipers.
Clamping Force:88-89 2x2x.785=3.14 inches squared
90-91 2.09x2.09 x .785=3.429 inches squared.
3.429/ 0.518= 6.620:1 clamping force ratio (smaller ones 3.14/0.518=6.062:1 clamping force ratio)
5.425/6.620= the stock clamping force is 81.95% of the Honda clamping force. 6.620-5.425=1.195/5.425=.220 or 22% larger
5.425/6.062= the stock clamping force is 89.5% of the Honda clamping force. 6.062-5.425=.637/5.425= .117 or 11.7% greater.

Brake Pads:Brake pads were listed on the sticky as being larger than GT(i)s by varying amounts. I did find a brake pad outer dimensions of length with metal tabs at 132.2 mm and a width of 49.3 mm. Our pad is 115.5 mm with metal tabs (98.425 mm without tabs) and 38.1 mm wide. However, the Honda pad is a different shape so you cannot directly compare end lengths. Best educated guess is that the Honda pad is right around 10% larger.

Rotors: rotor diameter: 242 mm or 10.32" there may be some variation on rotor sizes.
242/250 = The Honda rotor is 96.8% of the stock rotor. 250-242=-8/242=.033 or 3.3% smaller This will decrease torque stopping force. However, you are not using the Honda rotors with the swap. You use our stock rotors, which means no gain or loss.

The Honda caliper will give you access to more brake pads. It sounds like the Honda pads fit all the way on the our stock rotors. In my opinion if your racing a car and want to use non-street legal pads the coefficient of the pad surface available for the Honda calipers will make it worth it. If your using street legal pads the gains in my opinion will be negligible. The Honda calipers on Rockauto are under $50 a piece. The front brake mount for those years Honda should be 5.51" and ours is 5.5". Wilwood does sell a Dynapro Honda Acura caliper with the 5.51 lug mount, but it would require more investigation to how it would fit or work. Given that our Stock brake rotor is 250 mm and the Dynapro Honda caliper is for 262 mm the pad alignment may be off. Either way the rotors that go with won't work. More information on this can be found on the Teamswift archives under Honda Brake Caliper Sticky

The following are for the different piston sizes surface area for the Dynapro Radial Mount Calipers (they are four piston calipers, but you only use 2 to calculate not 4)
1.75 x 1.75 x .785 = 2.404 x2 = 4.808
4.808/0.518 = 9.282:1

1.62 x 1.62 x .785 = 2.060 x 2 = 4.120
4.120/ 0.518 = 7.954:1

1.50 x 1.50 x .785 = 1.766 x 2 = 3.533
3.533/0.518 = 6.820:1

1.38 x 1.38 x .785 = 1.495 x 2 = 2.990
2.990/ 0.518 = 5.772:1

1.25 x 1.25 x .785 = 1.095 x 2 =2.453
2.45/ 0.518 = 4.736:1

Some more math and things to think about. You do not want to just throw on the largest calipers in the front and do nothing to the rear. Here is a great article about that:

https://ebcbrakes.com/how-to-choose-the ... brake-kit/

The article explains roughly where the stock brake setup is. You have an uneven balance between front to back; heavier in the front. If I find the time I'll show the numbers. These are just a few of things to consider when calculating the bias: wheel base, maximum inertia force, driving style, base height, suspension setup, and of course front and back weight.

STOCK SETUP: The front to back system was setup in these ratios:

Clamping Force: Front clamping force/ (rear clamping force x proportioning ratio) I don't know actually what the proportioning ratio is. Next time I have my lines apart I will do a volume test between front to back over x amount of time. This should get me in the ball park. Let's take a guess 25%.
5.425:1/(2.114:1 x .75) = 5.425/ 1.586, 1.586/5.425 = the rear clamping force is 29.2% of the front clamping force, 5.425-1.586=3.839/1.586=2.42 or the front clamping force is 242% greater, or the front is 3.421 times the clamping force of the rear.
Remove the proportioning valve from equation to simplify the math; ratio comparison will work with or without because you will be applying the same proportioning valve to both systems and it can act as a constant. Additionally, as state I don't have the ratio of the stock proportioning valve which makes those number theoretical until that actual ratio is measured.
2.114/ 5.425 = 39%; the rear clamping force is only 39% of the front clamping force, or flipped the front is 2.566 times the clamping force of the rear. 5.425-2.114=3.311, 3.311/2.114= 1.57, or the front clamping force is 157% greater than the rear.

Disc Rotors: 240 mm rear discs/250 mm front discs = the rear disc diameters is 96% the diameter of the front. 250-240=10, 10/240=.04, or 4%. The The front diameters are 4% larger than the rear disc diameter.

Pads: Front stock pads are 5.787 inches squared. I have not accurately measured out the rear pad yet; rough measure was 3.55 inches squared.
3.55 / 5.787 =.613, or rear pads are 61.3% the inches squared of the front pad area. 5.787-3.55=2.237, 2.237/3.55= .63. The front stock pads are 63% larger than the stock rear pads.

Comparison of the front to Back System with only the Front Wilwood Setup:

Clamping Force: 2.114/9.282 = .228, or the rears are only 22.8% of the front clamping force. 9.282-2.114= 7.168/2.114= 3.39, the front clamping force is 339% greater than the rear clamping force. 339%-157%= 182%, 182% ratio change forward from stock bias.

Disc Rotors: 240 mm / 298.45 mm = the rear disc is only 80.4% of the front disc diameter. 298.45-240= 58.45/240= .244, or the front discs are 24.4% larger in disc diameter than the rear discs. 24.4%-4% = 20.4% ratio change forward.

Pads: 3.55 / 6.36 =.558, or the rear pads are 55.8% or the front pads. 6.36-3.55=2.81/3.55= .792. The front pads are 79.2% larger surface area than the rear pads. 79.2%-38.7% = 40.5% ratio change forward

These numbers are ridiculous since a 10% change is a major change in braking balance. Currently I am running it this way and will post up some measured data to compare the stock 60 to 0 numbers with the out of balanced numbers. I am going to guess that I am still getting shorter numbers right now, but not where I want to be. Right now I simply am not taking advantage of the rear brakes which doesn't make sense. When I'm done for the type of driving I do I would like to offset the stock forward balance by 10% either through caliper and rotor change or through adjusting the proportioning valve.

Rear Forged Dynapro Low Profile Lugmount Rear Setup with Comparison Ratio to Stock:
Clamping Force:1.12x1.12x.785x2=1.98/.518= 3.82: 1 clamping force ratio, and a reminder that 2.114:1 is the stock clamping force ratio.
2.114/3.82 = the stock rear clamping force is 55.3% of the Dynapro rear low profile caliper clamping force ratio. 3.82-2.114= 1.706, 1.706/2.114= .807, new calipers have a 80.7% greater clamping force than stock calipers.
9.282-3.82= 5.462/3.82=1.43, new setup fronts are 143% greater clamping force than rear,
5.425-2.114=3.311/2.114=1.57, old setup fronts are 157% greater clamping force than rear. 157%-143% = there is only a 14% increase in the bias toward the rear calipers.

Option 2: Dynapro Lugmount Caliper
I realized that the mount for these are the same 5.25", and the offset is only .01 different and the mount height is only .03 different. This would be some easy changes either in Freecad, or when you enter your G-code. This caliper offers a smaller piston and two larger piston selections. The larger ones would not be good, but the 1.58" bore pistons would still be an improvement from stock, and would be a larger brake pad of 6.36 . This would be the same size as the front, which is not great, but there are positives for these calipers. First the 6.36 uses a pad blank that is more readily used with more pad options, and they are a cheaper price. Second, the clamping force is less for the calipers smallest pistons. The lesser clamping force might be more appropriate with someone that uses 11" rotors in the front, or even someone who goes for a smaller piston up front.
Clamping Force: 1.0x1.0.785x2= 1.58 in squared
1.58/0.518=3.05:1 clamping force ratio. A reminder stock rear clamping force is 2.114:1
2.114/3.05=.693, or the stock clamping force is 69.3% of this option 2 rear calipers clamping force.
3.05-2.114=.936/2.114=.443, or option 2 has a 44.3% greater clamping force than stock rear clamping force.
((1.75x1.75x.785)2)/.518=9.282-3.05=6.232/3.05=2.04, this caliper setup leaves the front calipers being 204% greater clamping force than the rear.
5.425-2.114=3.311/2.114=1.57, old setup fronts are 157% greater clamping force than rear. 204%-157%= 47%, the front clamping force in this setup is 47% greater than stock. I would use this if you were stepping down in caliper pistons size in the fronts say to 1.62".
7.95-3.05=4.9/3.05=1.61, this caliper setup leaves the front calipers being 161% greater clamping force than the rear. 161-157= This is only a 4% increase in clamping force toward the front over the stock setup. This setup would potentially decrease the chances of needing a larger brake booster.

Brake Rotors:240 mm/279.4 mm = .859, the stock disc diameter is 85.9% of new disc diameter. 279.4-240=39.4/240=.164, the new disc are 16.4% larger than the stock rear disc diameter.
279.4 mm (11" discs)/ 298.45 = the rear disc diameter is 93.6% of the front. 298.45-279.3= 19.5/279.3=.07, or the front disc diameter is 7% greater than the rear. 7% - 4% = 3% increase in rotor size toward the front.

Pads: Brake pad surface area: 5.1 inches squared.
3.55/5.1= .696, or the surface area of the old rear pad is only 69.6% of the surface area of the new rear pad. 5.1-3.55=1.55/3.55=.437, the surface area of the new pad is 43.7% larger than the surface area of the old pad.
5.1/6.36= .802, or the surface area of the rear pad is 80.2% of the surface area of the front pads. 6.36-5.1=1.26/5.1=.247, the surface area of the front new pad is 24.7% larger than surface area of the rear new pad.
63%-24.7%= 38.3%. The bias ratio front to back for surface area of brake pads has decreased by 38.3%. This increases the bias toward the rear for brake pad surface area by 38.3%.

The whole idea here is not to throw the stock front to rear ratios off by much. I don't have a way to accurately compare the percentages from clamping force, rotor diameters, pad surface area, and other variables like brake pad coefficients. Therefore, the comparison ratios all need to be kept separate. As long as the separate ratios are not drastically altering from stock I'm taking advantage of the laborious testing that Suzuki engineers did in the first place. Although, I cannot add the separate variables I can still in a general sense talk about the outcome scope that I would like. I would like to offset the front biased toward the rear by 10% collectively. My reasoning behind offset the stock balances rearward by up to 10% is the lowering of the vehicle will reduce the kinetic weight transfer forward, and like the article above my driving style is more hands on.

Total difference between new and old:
clamping force front: new 9.282:1, old 5.425:1, 71.1% greater
rotor diameter front:new 298.45 mm, old 250 mm, 19.4% greater
brake pad surface area front:new 6.36 in sq, 5.787 in sq, 9.9% larger
rear clamping force: new 3.82:1, old 2.114:1, 80.7% greater
rotor diameter rear: new 279.4 mm, old 240 mm, 16.4% larger
brake pad surface area rear:

Thoughts on Rotor Selections:
You would not want to use 10.75" rotors in the front, and 11" rotors in the rear. If your using 11" rotors in front and in back, my suggestion would be to increase proportioning valve bias toward front. If your running 10.75" or 11" rotors in front and no changes in the rear (stock setup in rear) I would suggestion not going with 1.75 pistons for the caliper, and instead go with 1.5 or 1.62" pistons and still increase the bias of the proportioning valve bias toward rear. You can crunch through the numbers to see how the bias would change, and real world testing will be the only way to achievement maximum results.
Last edited by GT4LIFE on Fri Aug 10, 2018 11:14 am, edited 26 times in total.
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Brake Booster and Master Cylinder Thoughts:

You may need to increase the size of the brake booster due to the increase in the total surface area of the brake caliper pistons over stock. Stock power brake booster has a diaphragm diameter of 6.60". I need to compare this with the Vitara brake booster. The 1999 to 2005 Grand Vitara has a brake booster diaphragm of 8.79". The 2006 to 2012 Grand Vitara has a diaphragm of 10.67". It looks to have the same mounts, but I have not fully looked into anything. I'm guessing the diameter of the 10.67 one would be to big for the space, but again I have no idea. I have purchased a Suzuki Vitara brake booster from 1999 to 2005. The pedal feel with just the fronts on is slightly longer, but with more control over lock up. The only way to document the effects of this other than stating the feel is do separate testing from 60 to 0. I will have to do one set of ten stop with just the Wilwood front setup on, and then put the larger brake booster on and do another set of ten stops. I will then put the rear Wilwood system on and do another set of ten stops. Then at least there will be some data to support the before and after effects of the brake booster.

Master Cylinder Changes:

The problem with increasing the size of the piston(s) of the master cylinder is that it will decrease the clamping force at every caliper. This is why on redlinegti that someone recommended not increasing the master cylinder, but instead switching out the brake booster for one that generates more force. The other thing that can be changed is the pedal leverage arm ratio. Both the pedal levrage arm ratio and the brake booster will increase the amount of force added to the equation without change the clamping force.

Example: Master cylinder 1"= surface area of 1x1x.785= .785 inches squared
Stock Maser cylinder (13/16) .8125" = surface are of .8125 x .8125x .785= 0.518 inches squared.
There are 7/8 master cylinder .875= .875x.875x.785= 0.601 inches squared.

Take the calipers that I'm buy 120-7380
Total surface area= 4.8 inches squared.
4.8 divided by .785 =6.1:1 x say foot pressure of 100lbs = 611 lbs per square inch of clamping pressure.
4.8 divided by .601 = 7.97:1 x say foot pressure of 100lbs = 797 lbs per square inch of clamping pressure.
4.8 divided by 0.518 = 9.3:1 x say foot pressure of 100lbs= 930 lbs per square inch of clamping pressure.
611/930=34% decrease in clamping force. The 1" master cylinder would put the car almost right back to where the car starts with the same clamping force as the stock set up. The 7/8" master cylinder would be the only master cylinder that you could use to increase volume of fluid. However, if my math hold true leaving this as a force tranfer you can get the same force on the calipers by increasing the brake booster.

Just to try to clarify: I keep reading about volume of fluid of master cylinder used in a way that is not clear, and slightly misleading. Everything is best left as a force. A person puts x amount of force on the brake pedal (to keep thing simple lets say x is 100 lbs of force). The brake pedal itself works as a leverage ratio multiplier (a common ratio for the brake pedal is 6:1). 100 x 6 = 600lbs of force. The piston on the end of the brake pedal lever than goes through the brake power booster. This adds vacuum force to the backside of the brake piston and is added to the force already applied. The combined force than pushes the brake piston. Our master cylinder divides the combined force between left front and right rear, and right front and left rear in a two piston master cylinder equally. Two factors for the master cylinder: 1st the surface area of the master cylinder pistons, and the 2nd is the volume of displacement of the pistons. The net surface area of the brake calipers pistons divided by the surface area of the master cylinder piston will give you clamping pressure. Think of it as how fast a river is flowing. The volume equates to how much brake fluid is going to be moved. Think of it as the size of the river. The force of the river will be the speed of the river multiplied by the size of the river. Then apply this back to brake fluid. The larger net opposite force of the caliper pistons will require more force to move it. If nothing is done you will need to push further down on the brake pedal to get the full leverage of the pedal to increase force to compensate for the increase opposite force. Likewise you can increase the diaphragm of the power brake booster to compensate that force. This is where people want to increase the size or speed of the river. This would equate to increasing the diameter and/ or the length of travel of piston(s) of the master cylinder. The diameter increase would increase the surface area of the piston proportionately and at the same time inversely decrease clamping pressure. Just changing changing the diameter and consequentially the surface area will not by itself increase applied force. The increase in volume I think will move the piston with less pedal travel length, but again it will decrease clamping pressure. The increase in volume I believe will increase the opposing force at the master cylinder. The driver will be increasing the amount of force applied to the brake pedal to move it the same distance. This will most likely give a firmer shorter pedal length, but again reduce clamping pressure. This will not occur in quiet the same way if the volume change is only from increase in length of travel of the master cylinder piston(s). I believe this will increase the opposing force in the master cylinder, but not as much as increasing the diameter. This should give the brake pedal a slightly firmer pedal feel, and only slightly decrease the length of travel.

This article below and others that I have read for the most part ignore volume probably because it doesn't really play a part in solving this problem. The articles simply talks of pressure as hydraulic pressure. This is not to say that the master cylinder surface area does not need to be matched to the net (effective) caliper piston area. It must be calculated, but it is not a good solution to adding force to compensate increase in opposing force of larger calipers. Better solutions again would be to increase pedal leverage, or increase diameter of power brake booster. Additionally, I don't think you will find a master cylinder that has the same diameter with a longer bore that fits are car.

Article to help:

http://www.stoptech.com/docs/media-cent ... ng-systems

Rear Brake System Part List: This is the list used with the Dynapro 4 Piston Radial Mount Dust Seal with 1.75 diameter pistons calipers in the front.
1.Forged Dynapro Lug Mount Low Profile calipers 120-12160-BK (powder coated black, also comes in red, anodized, and polished).
1.a Alternate Caliper: Dynapro Lug Mount Caliper 120-9706.
2. Big Brake Hat Short Offset 6x6.25 undrilled 171-8975.
3.SRP Drilled & Slotted Rotor 160-7099-BK passenger side (there are other choices for rotors, but you still need .81 width and 11")
4. SRP Drilled & Slotted Rotor 160-7100_BK driver side.
5. Two EAR-916104ERL brake line fittings. (same as front)
6. Two FRA-650225 brake line fittings.
7. Brake Pads depend on caliper selected, Low Profile BP-10 Smart Pad 150-11363K.
8. Rear Mount Low Profile DXF Files:
9. Rear Mount Free Cad File:
10. Hardware: Four 3/8-24 or 3/8-16 bolts x 1.1875", existing hardware should work for mount; once the spot caliper is on two of the bolts will need to be lengthened.

I also showed my machinist the diagrams for the rear brake mount. He didn't like the slant of the front piece due to the difficulty of cutting the angled bevel out. He suggested fillet the edge. I think this will be fine, but I still need to pull the rear end back apart to double check. Once I send him the dxf files it will not be long to get the part built. I'll double check my funds and see what I can purchase to complete the rear setup.


Rear bracket update:


I rotated the holes in order to change the caliper to the front facing. This will do a couple things for me. It will make more sense with rotational inertia force and stopping brake force, and it will allow me to mount the mechanical spot calipers in the same spot as stock to hook up the emergency brake hand cable.
Last edited by GT4LIFE on Fri Aug 10, 2018 11:54 am, edited 7 times in total.
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I have covered most of the front brake system above and included most of the parts, but I will consolidate the requirements if you are going to use an alternate size disc rotor diameter.

There are four Wilwood alternate disc diameters that are .81" in width other than the 11.75" one. There is a 10.75", a 11",a 12", and a 12.19".

The 10.75" and 11" will use the 6x6.25" hat 171-8975. This hat has a .77" hat offset and a thicker face of .32" The face does not effect the offset. .77 - .73 = .04" = 1.016 mm difference. The rotor diameter difference for the 11" is .75/2= .375". Currently I am using roughly 3/16" (.1875") spacing for height. This will not bring it down enough to fit the 11" discs. The rotor diameter difference for the 10.75" is 1/2 = .50". I will adjust the dxf files above to adjust for these differences and post it here. I will take the .50-.1875" =.3125" + .035" shim width for adjustment = .3475". The 11" will need to use more spacers to bring the deck up to height.

DXF files front and top for 10.75" and 11" rotors:

The 6 x 6.25 hat is a blank and will require the center bore to be drilled out to 64.1 mm ish and the 4 x 114.3 holes to be drilled along with the set screws. The hat inside diameter clearance is listed as 5.10, but I believe it technically will clear 5.25 which is spindle diameter. I am using these hats on my rear brake setup and will adjust this as needed when I get there. There is a chance that the inside diameter will need to be lathed a 1/16". I already have the hats on hand, but have not drilled the center bore or lug holes yet. This will not effect anything structurally on the hat. I would switch to 12mm x 1.25 x 30 mm bolts, and the studs may need to be cut down to fit correctly.

The 12 or 12.19 rotors will most likely require 16" wheels. However, I'm going to list the clearance for the 12.19 is 6.77" outside radius or 13.54" diameter. The 12" radius is not listed but if you take the .25/2= .125" and add 6.57" the outside radius for the 11.75" it will equal 6.695". 6.695 plus minimum clearance of .08 = 6.775" or 13.55" diameter. If you use the 1.22 offset hat 171-8976 this will bring you in .49". As above you would flip the bracket and mount on the other side of the mount. My 15" wheels might clear at that .49" mark with the 12.00 rotors. Both height and width will need shims and possibly longer bolt of 12 mm x 1.25 x 40 mm. The same studs will work with the 12 rotors, but I'm uncertain of the 12.19 rotors. You would use the 11.75" bracket.
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Stock front data before change:

I completed the before brake test. I did ten passes from 60 to 0. The road conditions was dry and 73 degrees f. There was a 8 mph West North West wind. The vehicle was heading do West for all tests. I had exactly a 1/2 tank of gas, and 1 passenger, 55% humidity, no precipitation, and with the windows were up. I will try my best to test again after installation with the same or similar conditions.

1. 164 feet this trial I ruled as an invalid outlier as I know I didn't brake until well after the line.
2. 141 feet 6 inches
3. 184 feet 8 inches I fully locked it up and I will remove as an outlier also.
4. 155 feet 3"
5. 145 feet 4"
6. 137 feet 6"
7. 145 feet 4"
8. 138 feet
9. 168 feet
10. 146 feet 6"

11. 159 feet (no passenger).

8 runs total = 1178 feet and 1 inch
1178/8= 147.25 feet average

The GTi brand new was reported to have a 60 to 0 average stopping distance of 125 feet. There are a number of reason why I might not be getting close to that number. Here are few reasons:The system is 26 years old, my calipers and rotors are not new, the pavement was not super smooth asphalt, the original test was done using a GT(i) which is lighter than the GT, I had a passenger in the car, and my test line was a little difficult to see.

However, I am running stainless steel brake lines, and I have 195 50 15 on with BF Goodridge Super Sport Comp 2 tires.

The important thing is that I complete the test using the same conditions and variables with the new brake system.
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Rear mount files and updated front files are with machinist. I also dropped off the rear hats to have them lathed and drilled. I am also getting one more set of the fronts made. I wanted to thank JohnP from Teamswift for completing all the machine work, and bringing this project to life.

I'll post up the mounts and hats when I get them back. When I am happy with the fitting I will post up the dxf files. I still need to get the the brackets and mounts anodized, and design the small bracket for the spot caliper. Designing the bracket for the spot will probably require a phone call to Wilwood or purchase the one to get the measurements for the mount. Their online diagram for it is not great. I'm going to go ahead and remove the do not post line from the top. Please let me know what you think, or if you have additional questions, or comments.
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Thanks for all the work you're putting in. I'm looking forward to the project completion and comparison results.

I would also be interested in a price from John to supply a conversion kit (minus the calipers). He would need to supply the rotors due to the required machining. The stock calipers are starting to become hard to find so a conversion is probably a good idea for people wanting to keep their cars for a while into the future.
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