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Suspension, Brakes, Drivetrain discuss the wondrous effects of boost and your miata...

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Old 12-28-2009, 11:50 PM   #21
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Emilio,
Any clue if the fronts will clear 6UL-1 in 15x8 +40?
Not even close. Probably 10mm spacers.
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Old 12-29-2009, 04:22 AM   #22
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Not even close. Probably 10mm spacers.
Interesting. Im pretty sure my Mini Cooper 11.75" Dyna Pro kit would fit.
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Old 12-29-2009, 04:41 AM   #23
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A local guy here has a Goodwin V3 kit on a a fast N/A with ABS and a 1" 929 MC. Those are the best feeling Miata brakes I have ever drioven buy a faior margin. So yes, +1 for the 929 MC. Tricky part is the hard lines are different on the different year Miatas so there is no one PnP MC. You have to make some hard lines. For those of use that have the right flaring tool that's easy. If not, you either want to DIY Cunifer lines or invest in a $300 flaring tool. The cheap flaring tools are worthless.

You want a bigger MC and smaller caliper pistons for reduced leverage/stiffer pedal. Bigger caliper pistons give you more leverage (power)/softer pedal.
Thanks for the input.

On one of my GTX’s I have 4 piston 1.75” front calipers and single piston 1.38” Rx7 rear calipers with a 1” diameter 929 Master Cylinder. The brake bias works out good on that car with this combo because it has 67% of the car weight on the front tires statically. Problem is the brakes still feel mushy compared to my Miata with 1.38 4 piston fronts and 1.25” single piston rears and a just a 7/8” MC and the same rotors. I still think I want my Miata less mushy even though I have never felt a Miata with better brakes than mine.

Seems like the V8R kit would need bigger than 1” MC with those big piston calipers all around to feel good.

Also what about ditching the power assist. I hate the feeling of uneven brake assist due to throttle blipping while braking. Seems like the check valves never really hold vacuum right in some situations. A bunch of my Rally friends disconnect the vacuum entirely because they are using brakes and throttle together a whole lot but they are doing it on gravel where you simply cant use full assisted braking power anyway.

Bob

Last edited by bbundy; 12-29-2009 at 04:52 AM.
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Old 12-29-2009, 04:57 AM   #24
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. I still think I want my Miata less mushy even though I have never felt a Miata with better brakes than mine.
Confused. So yours are the best Miata brakes you ever experienced or unsatisfactory?

The V8R kit components are sized correctly. I'm not much with math but you calculate the leverages with the piston area and MC bore and it adds up to less leverage than the OEM system which is what we are after.

Last edited by emilio700; 01-20-2010 at 04:07 AM. Reason: F7
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Old 12-29-2009, 02:15 PM   #25
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Confused. So your the best Miata brakes you ever experienced or unsatisfactory?

The V8R kit components are sized correctly. I'm not much with math but you calculate the leverages with the piston area and MC bore and it adds up to less leverage than the OEM system which is what we are after.
Not unsatisfactory just curious if it could be better yet. I understand the math and I have my own spreadsheet for that. What I have found is the math is still not a perfect substitute for trial and error.

The leverage ratio is a simple thing to calculate. The sponginess feeling which arises from component flex and fluid compressibility because of trying to contain the pressurized fluid is a bit more complicated than a simple math problem. Iím not certain but it seems larger fluid volume systems operating at lower system pressure ranges exhibit more sponginess behavior based on my limited trial and error.

Bob
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Old 12-29-2009, 03:00 PM   #26
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Not unsatisfactory just curious if it could be better yet. I understand the math and I have my own spreadsheet for that. What I have found is the math is still not a perfect substitute for trial and error.

The leverage ratio is a simple thing to calculate. The sponginess feeling which arises from component flex and fluid compressibility because of trying to contain the pressurized fluid is a bit more complicated than a simple math problem. Iím not certain but it seems larger fluid volume systems operating at lower system pressure ranges exhibit more sponginess behavior based on my limited trial and error.

Bob
The additional volume could contribute to increased compressibility. We have also measured quite a bit of flex in the brake booster and particularly the firewall itself. A brace projecting rearward from the shock tower to the nose of the MC or its mounting flange helps a bunch.
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Old 12-29-2009, 03:24 PM   #27
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Bbundy,

Emilio brings up an interesting point about flex. An MC brace is on my long list of future projects too. If you do it it will likely be long before I get around to it. Let us know what you think!
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Old 12-29-2009, 04:36 PM   #28
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Bbundy,

Emilio brings up an interesting point about flex. An MC brace is on my long list of future projects too. If you do it it will likely be long before I get around to it. Let us know what you think!
Yep MC brace is on my list too. I've been wanting to do the 1" MC for a while
Just never got around to it. It will require some brake hard line modification.

I just found it interesting that the V8R kit uses what appears to be a 1Ē Wilwood MC that requires an adapter and it uses the same size piston calipers that I tried on another car that seemed like it could use a bigger than 1Ē MC.

FWIW it looks like Wilwood maks a 1-1/16 MC that is a direct boltup to the stock booster without an adapter. 260-4893. The only problem is the size of the otlet flare fittings are huge.

MasterCylinder

Bob
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Old 12-29-2009, 11:05 PM   #29
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I’m not certain but it seems larger fluid volume systems operating at lower system pressure ranges exhibit more sponginess behavior based on my limited trial and error.
Larger piston bores in caliper bodies mean less-stiff caliper bodies. This is illustrated perfectly here

StopTech Caliper Stiffness Discussion - see chart at bottom of page

where the caliper with 36 & 40mm pistons is stiffer than the otherwise identical caliper with 40 & 44mm pistons.
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Old 12-30-2009, 03:00 AM   #30
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Originally Posted by SolarYellow510 View Post
Larger piston bores in caliper bodies mean less-stiff caliper bodies. This is illustrated perfectly here

StopTech Caliper Stiffness Discussion - see chart at bottom of page

where the caliper with 36 & 40mm pistons is stiffer than the otherwise identical caliper with 40 & 44mm pistons.
Yea but the chart says shows it as a function of pressure the larger piston will be aplying more clamp force at the same fluid pressure. The chart is tiny and hard to read but I wonder what the curves look like if you convert the lower axis to clamp force rather than system pressure. I bet they would be pretty darn close to being on top of each other for the same caliper configuration with different piston sizes.

Iím guessing the stiffer feel is more because the brake lines and the fluid compressibility are nonlinear and they behave like stiffer springs at higher pressures. It requires the same amount of clamp force at the caliper to slow the car down at a given rate and using smaller pistons all around to provide that clamp force requires higher system pressure. The lever ratios all work out so the pedal force required is the same but the higher system pressures put the flexy bits into a stiffer portion of there spring rate curve.

The correct amount of stiffness is subjective as well. I donít think it would feel right if the pedal didnít move at all ether.

Bob
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Old 12-30-2009, 03:14 AM   #31
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The correct amount of stiffness is subjective as well. I donít think it would feel right if the pedal didnít move at all ether.

Bob
Drive a GT3 if you get a chance. Some Porsches modulate with pressure, not distance. Personally, I like it.
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Old 01-01-2010, 06:09 PM   #32
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My God, this system with a proper set of tires would be sick.
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Old 01-20-2010, 03:27 AM   #33
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I hate the feeling of uneven brake assist due to throttle blipping while braking.
Some ideas:
1) add volume to the vacuum reservoir of the brake booster
2) place a vacuum regulator between the manifold and the booster, set it to 12" or 15" vac, whatever. This would also require more force for the pedal.
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Old 06-01-2011, 10:18 AM   #34
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So, I currently have:
- 94 OEM MC
- 94 OEM Booster
- Front: 4-pot Dynalites fro Goodwin V4
- Rear: 94 OEM (relocated)

Currently pedal travels alot. I have the V8R MC kit here. I will mount this soon.
Travel will decrease, effort will increate.

Is the 94 OEM Booster enough? Or should I go larger? Currently I could do with a bit more effort, but another car with the same setup but 6-pots up front is very heavy IMHO.
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Old 06-01-2011, 02:59 PM   #35
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Compressible pad = more pedal throw
pad taper = more pedal throw
bad wheel bearings (rear) = more pedal throw

I stopped those three issues and the problem went away with pedal throw. I later added a super-baller 2001 MC and couple with the 11.75" front rotors, this car feels awesome on the brake pedal. I wouldn't say the larger MC is required
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