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BBK for MSM - Confused

Old 03-18-2018, 01:01 PM
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Default BBK for MSM - Confused

Been reading the various threads on brake kits for a few years now, but I've never taken the plunge on account of the MSM's stock brakes never seeming overwhelmed. However, over the the last couple of summers, I've started using Maxxis and Hankook slicks and I'm starting to see faster pad wear and noticeable fade on hot days, so I'm looking hard at an upgrade. However, I've been a bit bewildered by the range of comments and the underlying assumptions/conditions attached to them in respect of master cylinders, boosters, and their compatibility. So hoping for some help...

The big challenge for me has been the fact that most commentary compares the feel, pad life, thermal capacity, etc. of a given BBK to NA/Non-sport brakes. From what I can tell, the Sport Brakes have considerably larger and thicker pads, in many instances rivalling the dimensions of many BBKs. The other points of confusion have been bias, pedal travel, and pedal feel. These seem to be driven by master cylinder, piston sizes, and booster. I might be wrong, but the MSM booster seems special, too.

Car & Usage Pattern: 2004 MSM
  • FM Big Enchilada
  • 949 Xida Gen 2 900/500
  • FM front bar on stiff, MSM stock rear bar
  • Gutted and trailered
  • Track Days, Time Attack, Autocross
  • Tires: Mix of 225mm and 245mm Hankook RS4, Hanook Z214 C71/C51, Maxxis Slick
  • Brakes: Stock MSM with ABS; stainless lines and 2" ducts; handbrake removed
  • Pads: Only ever used Gloc. Current compounds are R10 or R12 in front and R8 or R10 in rear
    • This combination tends to give me one summer out of the fronts and two summers out of the rears
    • Open to using other pads, but not keen on anything made by Hawk
Near Term Changes
  • Car will get caged in near term and with that, more focus on running with slicks, including trying Hoosiers
  • After caging, aero will be next frontier
Objectives for Brake Upgrade:
  • Fit under 15x9 Advanti Storm S1 with spacer not exceeding 5mm
  • Maintain overall travel
  • Maintain or decrease pedal effort (wife also drives car at autox and track)
  • Stiffen pedal feel
  • Eliminate fade and increase thermal capacity
  • Increase pad life
  • Simplify servicing/pad changes
    • speed
    • eliminate parts that fall out/wear out
    • no more manual adjusters like those in the rear calipers
  • Buy once -- quality and capability headroom
  • Having achieved the above, minimize running costs
  • Weight savings -- everything is lighter than stock, so not a big preoccupation
I hope that covers the "we need more information to give you good advice" comments.

With all this in mind, I'm sure (although I remain open minded) of one thing: 11.75" front rotor and stock rear rotor is what I need. Beyond that, I'm debating between:

  • Stoptech STR42
  • Stoptech ST42
  • TSE Superlite
  • Dynapro 4-Piston
  • Stoptech 2-piston
  • Powerlite 4-piston
  • Is there anything else?
Honestly not sure which combination of these will:
  1. Work best with existing MC and Booster to preserve current pedal feel and travel without hurting bias
  2. Provide the best foundation of performance that could be made, through changes to MC and booster, to maintain overall travel and effort while:
    • Maintaining overall travel
    • Maintaining or decreasing pedal effort (wife also drives car at autox and track)
    • Stiffening pedal feel
Any input to help me plow through this would be appreciated. If I've identified mutually exclusive objectives, please let me know.

An explanation of how to approach this problem (the math) would also be helpful. I've gotten snippets across many threads, but not confident in how it fits together or how parameters affect pedal travel, feel, effort, etc.

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Old 03-21-2018, 11:45 PM
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I am a bit of a MSM noob, but do the MSMs come with what mazda calls the "sports brakes"? Id say with your plans to change both front and rear calipers, an adjustable proportioning valve is a must. The only caveat is I know the NBs with the "sport brakes" & ABS do not come with any factory proportioning valve body. Either way this is a relatively cheap upgrade that will save you a lot of headaches down the line with not being able to tune the bias. Also I know you already mentioned it in point #2, but depending on what route you go with calipers, you are likely going to want to change MC size (although I dont know what piston diameter comes in the MSM). And yes I do believe you are correct that the MSM booster is relatively unique and not compatible with some (if not all other) MCs.

The other important factor I dont see discussed is a rough estimate of budget since BBKs can really vary wildly in price, unless this is of no issue.

Also (Im sure you've probably read some in other places) the science behind cylinder diameter and booster ratios are what really control the braking feel and effort. Multi-piston calipers generally use smaller diameter pistons, which (with the same MC) generally give a softer feel. A larger diameter MC will give you a "firmer" brake feel, but there is obviously a limit to how useful this can be. You just have to imagine the ratio of MC to caliper piston diameters as having a wider bore cylinder compared to stroke length when volumes are considered the same. Since fluid is not compressible the volumes between the two cylinders (master and slaves) always must be the same. A larger diameter master cylinder will require less stroke (pedal travel) to move the same amount of fluid volume as a smaller diameter one. There are some probably some math snippets that are around the web that will give you an idea of how to figure out your MC to caliper ratio.

Additionally when you talk about how much the brakes are boosted, this affects pedal effort. The brake booster is essentially a force multiplier, so for example if its boosting effort by 200%, then any effort you exert on the pedal is doubled on the MC. The initial thought may be that "more boost is better", but it must be realized that while it not only boosts brake pressure vs effort, it has the effect of turning your brakes into an "on-off" switch. An increase of boost ratio will decrease braking effort required, but will cause it to be more difficult to modulate.

I hope this information is somewhat useful and not repetitive from what you've already read!
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Old 03-21-2018, 11:54 PM
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Can't use a prop valve with ABS
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Old 03-22-2018, 07:52 AM
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Originally Posted by UrbanSoot View Post
Can't use a prop valve with ABS
Says who? The NAs and NBs (without sport brakes) with ABS come with a factory prop valve that you can replace with an adjustable one. Unless its something MSM specific (hence the question on sport brakes) then there shouldnt be any reason it cant be done. NCs and later with ABS however don't have a mechanical prop valve so its not an option.

You would however also probably want to disable your ABS while testing/setting up the prop valve so that you can better feel where the proportioning is going. (then re-enable once you're happy with the distribution)
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Old 03-22-2018, 08:16 AM
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My experience...I have wilwood radial mount fronts, oem sports brake in the rear... oem2001 LS master cylinder, with ABS. (sslines, and mc brace)

Pedal effort is significantly higher, the first couple months of driving with the new brakes, I thought they were worse than stock, because I wasn't pushing hard enough. I'd guess 60% higher effort.

A little stiffer pedal

My 2 cents... save your money, buy higher temp pads. Sure the big brakes look cool, but the oem sports brakes are MUCH more than powerful enough to lock up any tire you mount at any speed. Unless you are getting significant pad taper, which is halving your pad life, stick with sports brakes.
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Old 03-23-2018, 01:06 AM
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The ST/STR42’s are the best hydraulic match for your sport rears. IMHO just do that and you’ll be happy. No need of upgrading the rears. Sport calipers are pretty stiff. Not sure about wheel fitment though. That’s a V8R or Ryan Passey question. All of the 11.75” kits are gonna be tight with your wheels.

FWIW I run the STR42/sport rear/1” master. It’s a GREAT combinatio!
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