I've read this
Flyin' Miata : Chassis : Brakes : Complete adjustable brake proportioning kit
and several other reports saying you can't use a bias valve with sport brakes and ABS. Let's assume 2 things before we discuss:

1. Pretend my car is an '04MSM - it has the entire brake system from the donor car.
2. I'm not baller enough to drive on the track without ABS. Sure, many things would be better if I sacked up and turned it off, but let's say it stays installed and stays on for the sake of the discussion.

I'm running an XP12/10 combo with TSE ducts and can't make brakes fade no matter how much I abuse them but the fronts are wearing at about a 4:1 ratio which means I go through 4 sets of front pads to one set of rear pads. 6 or 8 days on the fronts and ~2 years on the rears. This wear pattern tells me I could improve overall braking and front pad life with some more rear bias.

The ABS doesn't engage very often. I feel it tickle the pedal once or twice a session if I overdrive something or if I'm generally flogging it to catch a Porsche or Corvette. It's not like I'm diving deep and mashing on the stop button for every corner although I am an admitted over-braker in general.

As I understand it, the sport ABS system uses electronic bias adjustment with no mechanical prop, unlike the non-sport or non-ABS systems. I know the hydraulic rear bias I want is built into the system because I have the ABS power on a toggle and the car is pretty terrifying without it - way too much rear bias to drive at the limit. The lawyers and accountants set the electronic rear bias for the factory system for street safety which means way more front brakes so hairdressers don't spin out in the rain. How do I trick it to let rears do their fair share of the work?

I can't think of a hydraulic solution that would send more bias to the rear and still let the ABS monitor it for lockup. It seems to be an electronic problem. Would going to balanced pads (XP12/12) help or hurt this? I don't know that 12s bite harder or do they? I thought it was more thermal capacity that separated the compounds.

A BBK may be in the cards over the winter but new front hardware wouldn't answer this riddle anyway. Any thoughts appreciated. Thanks for playing!

 

That's not the way I understand it. There is no electronic bias, but the ABS stops the rears locking up too soon and stops the hairdressers spinning out in the rain.

 

When I had my stock 03 and used it on track (with OEM pads, which were not too shabby I'd say), the rear (on the car ) was always presently happy.
Maybe some more rear bias would have been even better, but with it under electronic control, there isn't much you can do.
Less/more teeth on the ABS rings?

Playing with the hydraulics (pressure/pistons) won't help and you mention, and the mechanics (pads/disk diameter) will not help either.
Starting a project on the darknet to crack the ABS-ECU and reprogram it would make you king in the ABS-microuniverse, but such an undertaking needs the fuel of open source (which will not be that "dark").

When was the EBD introduced, 01 or 03 (my memory says 03 but I'm not sure at all)?
If there is a difference between NB2 replacing the ABS unit with one from a 01 could enable use of a old-fashioned bias valve.

 

All of the SE cars from '01 through the MSM had Sport Brakes and ABS although one or two of the models my have skipped ABS. Did the 10AE have sport brakes? Crusher had/has an ABS block with the system on a switch that they normally leave off except for when it is raining. Maybe Emilio can chime in on the setup.

 

EBD as using ABS to maximize the rear brakes at all times instead of using a prop valve.
But it might be all Sport brakes with ABS being the same, if so, no options.
98-00 use a normal prop valve and separate units for ABS ECU and ABS pump.

Reduce the rear bias (with ABS off) hydraulically or mechanically and turn ABS on when you need it?

 

From what I understand of the EBFD, it more or less operates like the prop valve is wide open then pulls bias away when it detects slip. And it can learn the situations that cause the slip. I'm sure it also has internal programming. So using a pad with a higher coef in the rear than what you have now could get you more rear bias, maybe but the EBFD might just change its thresholds again.

You will be using front braking equipment faster than rear in any car because they will be doing more work, unless its a very rear weight biased car with very non-grippy tires.

 

Ask yourself what happens when the ABS system suddenly malfunctions during a session/race. IMO, race cars with ABS should have the bias dialed in with the system 100% disabled, and only then should it be turned on (and only then in the rain, IMO). If the Sport ABS pump contains electronic bias fuckery, ditch it for a non-Sport pump that doesn't.

 

All the 01+ have the EBFD, and the 94-00 ABS, are not stand alone like the 01+ and also only 2 channel rather than 3 channel like the 01+. I wouldnt worry about any reliability issues. ABS is allowed in SM5, which also have EBFD, and you dont hear about scca people yelling and screaming about the death of a million babies because ABS is so dangerous on the track. And those cars stop like a mother ******.

 

One of the NASA ST2 Vettes from Norcal who was the smart money for the 2013 championship binned his car at Miller due to ABS failure. Pretty sure the CJ Wilson MX5 that lost to us at the 2012 T25 also lost time to malfunctioning ABS. My race cars will never rely on an ABS computer for proper bias.

 

ABS failure, or "ice mode"? Vettes are known to have ice mode issues with sticky tires, so it should have been disabled if class legal. Miata abs doesnt know what ice mode is.

 

Didnt the ABS module on the 01+ have two inlets? one for front and one for rear?
If you have too much rear bias with the ABS turned off, cant you still put a standard prop valve between the brake master and the ABS unit?

So as Savington recommended, cant you just adjust your bias with the ABS turned off so your car is still balanced even if you lose ABS for some reason?

 

But then the EBFD might not work correctly and would give you too much front bias. Well unless you changed the bias **** when you switched the abs on or off.

 

Then:Go from sport rear calipers to non-sport with Mtuned (or similar) brackets (or 11.75" up front)?
Even less friction pads in the rear maybe.

If the non-ABS dry bias is about right, the EBD cannot add more rear brake. When wet the bias will be ABS controlled but the max force is reduced.
But there is no pressure "knee" of course...

 

But remember, you want more rear bias in the wet than you do in the dry, because weight transfer.

 

This sounds like the most simple solution but I'm not sure if the system would work correctly at all with the ABS on. There must be a reason all of the literature says no prop valves on these systems.

Don't the earlier systems need some ECU help to function? One of the great things about this swap is that it bolted right in. I literally didn't need to bend a single hard line or source a single adapter. The ABS wiring harness just needs a heavy power source (30a), a lighter power source (15a), a good ground and the 4 pairs of wires to the wheel sensors.

What does Crusher have for ABS and how is it set up? I know it isn't run in the dry anymore. I'm pretty sure the Wilson crew just ate brakes with the ABS on like Crusher did in '11. I don't think they had an actual malfunction.

 

We set up our cars to have perfect brake balance w/o abs then race with the ABS on all the time, wet or dry. Pads last a touch longer with ABS off in full race conditions.

The most critical aspect of brake balance for low lap times in a medium to low hp Miata is the balance at low lines pressures. This is the area used for trail braking, delicately rotating the car into a turn at optimum slip angle with all 4 tires. If the straight line threshold braking bias is off by 25%, you can drive around it and still get max cornering speed. If you can't trail brake because low line pressure is off 25%, you're going to spend a lot of time sideways and being slow mid turn.

Adjustable proportioning valves only change the knee point to begin choking rear line pressure. At low line pressures when trail braking, the prop valve isn't even being engaged. This is important: Prop valves only affect high line pressure, straight line threshold braking.

If the brake balance at low brake line pressure is off, no amount of bias adjuster, ABS, On/Off switch will fix it. You simple screw up every corner entry, every lap. Getting the pad .mu, rotor diameter, piston area, master cylinder diameter, brake booster all right is key.

Crusher uses an NB2 ABS brain from an '01 IIRC. Prop valve. Sport brakes (2 pc rotor) in front with XP12. 94-00 rear caliper with Sport (2 pc rotor) and XP8 rear. Tilton prop valve, NB1 booster, Wilwood 1" tandem M/C. To date, I don't think it has ever been out braked on track by anything outside of a GT3 cup car or Radical.

BTW, Crusher has been sold as a nearly bare roller to a Socal NASA racer for PTE.

 

Thank you for the information. My car and driving skill are a little more brute force and ham-fists right now but it makes a lot of sense at my level to set the car up 'correctly' and then learn to drive it. I have some of the same setup - essentially everything from a stock '04MSM.

Sooo.... I need to pick up a prop valve, see if the NA8 rear caliper is different from sport caliper, get XP8 rear pads (currently XP10), see if the NB1 booster is different than the NB2/MSM and figure out what to do about the MC. How critical was the dual MC to the balance you achieved and do you see the OEM part having a chance of matching it? Also, I wasn't aware there were 2 pc rotors available for the sport brake rears. Does this facilitate the 'cooler' XP8 compound in the rear?

Bittersweet. I am proud to have touched a wrench to this historic vehicle. My team jacket with the rotor burn on the sleeve will never find its way to the goodwill box!

 

OK...

The Wilwood dual master looks somewhat affordable from 949:

Miata Race Master Cylinder kit

From Keith via M.net in This Thread:
Same thread and a user named SolarYellow510
From user J Man:

 

Emilio,

Was the booster in your setup from the NB1 ABS or non-ABS? It looks like I will be happier with the MSM booster at 6.4:1. The other question is how much effect the 1" MC has and if there is a ton of difference between the 1" 929 MC and the dual Willwood in terms of bias and pedal feel.

It looks like Crusher had strong front brakes and strategically handicapped the rear brakes with smaller calipers and less grabby pads. According to the information listed above, all miatas had 32mm rear pistons until the 35mm sports showed up.

After all of this hardware is sourced, how much are you actually asking the prop valve to cut? It seems like we are searching for ultimate mechanical grip before any hydraulic or electronic wizardry is employed.

I don't have any NA8 or NB1 rear calipers but I have at least 2 or three sets of NA6 rear calipers that show the same 32mm bore. Would they bolt to sport brackets over sport rotors? I've done lots of Miata rear brakes but never looked at them that closely.

Still curious if the 2 piece rear rotors were a typo in Emilio's earlier post...

I love my brakes now - ROCK hard pedal, fade proof, easy to modulate and predictable. The pad wear I mentioned in the original post is a concern but I don't see anything I have learned in this thread making that better so replicating Crusher's non-EBD balance seems to be the new focus.

 

Woot