Sparkley's Big Brakes (Called Sport Brakes in USA)
Now on the question of Brakes, should Sparkley go Big Brakes (NB8B, Standard Brakes (NA8) or Little Brakes (NA6) ?
Big brakes are more powerful but are heavier than little brakes, and that cuts down on ride and handling....so not a win-win unfortunately.
Mazda must have figured that the NA6 was down on power anyway, so no need for powerful brakes and the extra unsprung weight penalty imposed by upsized technology.
For
atmocharged Sparkley, I chose Big Brakes, the
largest Mazda NA/NB factory brakes available.
My reasoning was an atmocharged engine is not the hottest, so to keep things compatible, I realised that Big Brakes are not the hottest either.
But really, the Big advantage for Big Brakes is to give Sparkley decent sized rotors to set off a beautiful ABS Brembo Upgrade Kit like this within 15 inch rims and to offset the insulating effect of the ABS Brembos.

Note Big Brakes are too big for 14 inch wheels and in some 15 inch wheels like the Enkei RPF1.
Also note that NB8B front and rear calipers are not just mounted differently, they are a different specification from NA/NA8/NB std Calipers. Therefore to fit Big Brakes requires both NB8B discs and calipers.
Now to fit the ABS Brembos I used heat resistant reusable shiny metal thread
steel fasteners rather than the single use adhesive bonding agents normally recommended.
This will allow them to be easily removed for pad changes.
----------------------------Rear----------------------------------------------------------------------------Front
Risk assessment of any innovative fastening sytem is an important consideration as the ABS Brembos are made of an
High Temperature Industrial Quality Acrylonitrile Butadiene Styrene, of unknown specification.
In fact, ABS becomes amorphous and so could warp and bend at radiator temperature, so I am unsure of the number of stops achievable at the track before I hear the very close rim clearance established with the spinning rims, start to tighten with heat.
After each Sprint, I could perhaps measure ABS temperature around the mounting screws or maybe impact hammer test the ABS Brembos to hear if they ring like crystal or thud like rubber.
Armed with unbelievable engineering foresight, I even bought a spare set of ABS Brembos so I could bench test with a heat gun, the various phase changes with temperature, of the ABS used.
I have gone to all this trouble with ebay brakes because of their ability to suddenly stop people in the street at the lowest cost.
So now fingers crossed Sparkley will be slow enough for me to brag that I bagged
dual function street and track stoppers for just $35.
Otherwise I might have to take a screw driver to remove/replace them each track day with the track tyre change.
One may ask what about heat build up on the road say "coming down the range" ? Actually that should not be an issue.
That's because in an MX5 dríven with maximum Jinba Ittai, brakes are not used to descend down grades; lower gears and high revs are.
So there is only brake heat build up on initial entry to corners, and that build up under spirited driving is likely not significantly affected by highway road gradient.
So
the torture test for ABS Brembo's should be on the track with track setup and no limits, where entry speeds into corners are so much higher than on the road with road setup and legal limits.
It is a tortuous test on track because even though exit speeds may also be higher, thereby offsetting speed differentials, the maximum and average on-track brake power are much higher than on-road brake power.
Speaking of Stoppers, Sparkley's engine bay is not graced by a "separate stiff stopper" of the master cylinder, like this

but is instead graced by an
"integral stiff mounting" of the master cylinder, like this.
Critical AppraisalBrakes are primary safety items not just a fashion statement about who we are.
Therefore I figured its worth reviewing my work against
something prepared earlier by some kind person.
Used Brake HoseElastomers like brake hose do not last forever, they have a shelf life. I imagine the shelf life of a brake hose would be less than 10 years.
So even though my NB8B brakes are only 2003 and its hoses were looking "as new", it was their turn for the scrap bin.
But really that was a good excuse to shout Sparkley some new
HEL ADR approved braided lines long enough to reach the NB8B calipers as they are possibly
a bit of a stretch for 1997 brake hose length at the front.
Rim clearanceBig Brakes appear not to fit in
14" rims, however are fitted factory fitted inside 16" rims and factory Enkei 15" rims on the NB6B NRA.

Big Brakes fit the 15 x 7 Enkie LM8s, but not the
15 x 7 Enkei RPF1Space SaverBig Brakes also need a
larger diameter space saver spare. This does not fit an NA boot but found that Sparkley's boot could easily fit a
generic NC spare wheel instead.
Dust Shields I have fitted Big Brakes OK to an NA8 before by pushing the dust shields sideways a little to clear the disc. On an NA6 given their much smaller diameter shields a little
more elbow grease would be required. However since Sparkley is using NB8B uprights, spindles and brakes, the largest shields are already fitted.
Rear Brake Bias ValvesI found the NA8 valve with these brakes (the one with the orange band) to work OK with Darth, before Sparkley's gender transformation, but still there was room for a valve with more rear bias as I have still locked the fronts first even with extra grip from semi slicks at track temperature. Brake control is inherently more stable with a bit of front bias, but the NA6 brake proportioning valve is overly front biased in combination with sport brakes so definitely needs to be changed out.
Some info from
Flyin MiataWith Sparkley I have decided not to continue experimenting with bias valves, but rather use the complete NB8B brake system including the NB8B Antilock Braking System (ABS), an active control not in need of passive biasing to function.
It is so good to think that with this ABS as well, Sparkley is likely the only Female NA8 in the world with Twin Twins...Twin ABS Brakes and Twin Air Bags.
A later post will discuss Twin Air Bags.Master Cylinders and Brake BoostersThe NA6, NA8 and NB8a master cylinder and boosters deliver adequate pressure to the larger diameter calipers of Big Brakes but because of the smaller bore 7/8 " verses 15/16" is unable to deliver as much brake fluid required by the larger diameter calipers.
Therefore such a system is less tolerant to overheated fluid, entrained air, moisture, soggy brake hoses etc (more chance of running out of brake pedal). I imagine more regular fluid changes required.
It is also another excuse for adding stiffer braided lines ! Now for high temperature fluid, I will not be using DOT 5 Silicon fluid as it is proven too spongy.
Instead I have the system filled with
SCA DOT 5.1 ethylene glycol brake fluid at the moment.
Unlike Silicon Dot 5 which will last almost forever, Dot 5.1 fluid is hydroscopic so preferable if flushed every couple of years at least.
Interesting
info on the subject.
Legal RequirementsLight Vehicle Code of Practice is a good place to begin to reflect upon intended mods.
For example, after market adjustable brake proportioning valves are not recommended for road use. They can not be legally certified by an engineer because it is clearly foreseeable to the engineer that the brakes are simply adjustable to a different specification.
Use of OEM non-adjustable brake proportioning valves can be certified by an engineer if compliance required.
Use of NB8b brakes with NA6/8 master cylinders and boosters can also be certified by an engineer if compliance required.
However for Sparkley, engineer certification will definitely not be required as the complete ABS NB8b master cylinder, booster and control system is used unchanged from factory.
Also the ABS Brembos are really just fancy dust covers to keep Sparkley's shiny wheels clean, but no one being stopped on the street by them, are to ever know that.