The Powerlite rear option, if we were to pursue it, would strictly be a racing brake on the 10.9" Sport rotor for the 11.75" Superlite front and not intended for street use. But it is not something we are currently planning. Hubs first

 

Now you really have my attention...

 

I had the 1" pistons, smallest they offer. Stock 99 F/R ratio is 2.6:1, sport is 2.4:1, dynapro w/ 99 rears is 2.4:1, and dynapro w/ powerlite is 1.9:1.

Empirically the only way to get a decent pedal feel was a 1" master from a 929, and even with ABS it wasn't stable in high speed braking w/ sticky tires unloading the rear.

Perhaps the superlite offers larger pistons, I didn't investigate that because there weren't any kits offering it when I was trying to make this work. Running an M3 on track now, so it's moot from my perspective.

--Ian

 

Piston area ratio between front and rear is central but you also have to factor in the rotor diameter which affects the torque difference. Thus why we do not recommend running sport rears with 11 inch front rotors.

 

Yeah, I have a spreadsheet somewhere with the rotor diameters in it too. It tweaks the numbers slightly but doesn't make a significant difference to the end conclusion that the powerlite is way too much rear caliper for any of the common fronts.

(FWIW, I had the TSE 11.75" front kit)

--Ian

 

I'm really excited to see this. My main consideration in a BBK is consumable costs, and it looks like with the Dynalite calipers and ND rotors this ticks all the boxes for me.

My car makes between 220-250whp in "track" configuration (low boost), do you think I can get away with the 11" setup? I'm more of a weekend warrior than a track junkie, admittedly, but plan on hitting 5-10 events next season. My OE 1.8 brakes have been "doing the trick" (basically overheating every event, but not catastrophically), but I've been getting faster, and the faster I get the more they hold me back. Particularly after 4+ hotlaps.

I've looked into some of the pricier kits, but the cost of replacement rotors makes me cringe.

 

The 11" kit with ducts would be a big step up from what you have now but if you're making real improvement then the reality is you'll want the 11.75" kit. Note that most 11.75" BBKs including the one we currently offer have inexpensive replacement friction rings that really keeps consumables quite low.

 

...just stay away from the $33 non-directional 11.75" rings

--Ian

 

Thanks for the reply! I'll have to do some more research into your 11.75 kits and what friction rings it uses. I ended up with a goodwin racing BBK, and the only friction rings I could find that would work with that older kit were $200+ a piece. Ouchie.

 

Yikes. Probably their old DBA kit?

Any questions, email me. Info@949racing.com

 

OK, so for us folks that already have sport rears (2004 MSM) what is the optimal rear set up for use with the 11" ND rotor front kit which I am planning to order as soon as the "list" opens up?

What will the problem be with sport rears, too much rear bias?

Could this be addressed with an adjustable prop valve?

 

In our experience, the combination of the larger piston in the rear sport caliper and 10.9 inch rotor lead to too much rear brake torque assuming you use the same race compound pad front and rear with 11" front. I typically like to set up my cars with one step higher friction compound in front regardless of the system. When running Sport rear brakes with an 11 in front however I found I had to make a two-step change to get the balance. And that was with the rear brakes choked off with the prop valve which made the ratio between straight-line threshold and low line pressure Trail braking not work. The fix then was to use the smaller piston NA8/NB1 rear caliper on the sport rotor. That's a lot of Band-Aids and a choked down prop valve. Switching to an 11.75 front added enough front brake torque to allow a single compound step to the rear with sport rotors and opened up the prop valve.

This is been my experience over a variety of cars with a variety of different brake setups. If it is a streetcar running a low-friction street pad like the GS1, then pairing any 11 in front with rear Sports isn't an issue. I feel the imbalance only arises when you add much higher grip tires and race pads. Prop valve only affects bias above a certain line pressure threshold. Trail braking is very low line pressure. So that critical phase of releasing the brakes to rotate the car into the turn is unaffected by a prop valve. Prop valve only affects straight line threshold braking. To adjust brake bias that has you spinning or understeering on corner entries, you need to adjust the system without the prop vaalve. That means rotor diameter, piston area and and compound.

TL-DR : Switch to the early rear caliper (smaller piston area) and run a higher friction compound in front if you really want the 11s up front with Sport rears with race pads.

 

Thank you for your detailed response. You've answered my questions perfectly and included your viewpoints on the application.
You have added to my "mental" tool box (the trail braking comments).
This one is a street car that I built for a customer that will NOT be used in a track situation.
He's actually a member out at MSR but he's a bike guy that says "corners are not exciting until your knee is hitting the pavement".
This merely proves he is crazy...
The MSM is a street play toy only.
He's been bugging me for a BBK and everything I've seen up to now is overkill for his application.
I called him as soon as I saw your first post and we are ready to order NOW. I needed Level 1 BBK at reasonable cost. You have delivered!
Ok, you haven't delivered yet but you will...

The big assed open hole in the center is great.
This car does not need dedicated cooling tubes but a cooling scoop (ala 911 rear brakes) will be made.
Maybe you might think about making one...
We would order that as well.

Nothing you post is TL-DR
It never will be
Thanks again

 

Piston area ratio between front and rear needs to shift up or down depending on a variety of factors, but hinges primarily on friction coefficient of the pads and tires (mu).

As you reduce pad and tire grip, total forward weight transfer potential drops. Imagine braking on ice with slicks in a car with 50/50 weight distribution, or good tires but junk $20 no name pads. Virtually no forward weight transfer so same size brakes front and rear would still work.

Increase pad and tire grip; sticky race tires on a sticky track with lots of rubber on it. Massive forward weight transfer. This high mu example requires more total thermal capacity, the greater proportion of that increase in thermal capacity need up front.

As this pertains to cars, using a higher grip tire and pad than the OEM system was designed for will require a decrease in rear piston area if nothing else is changed. Just increasing the front piston area without changing the M/C size increases the pedals leverage, leading to a longer pedal. The brake are now capable of generating more torque for a given line pressure so the idea is to reduce hydraulic advantage, not increase it. So a smaller rear piston or larger M/C. Thus why our upcoming 11.75 kit for the NA/NB will actually have less piston area than OEM, to offset the big increase in front brake torque. With lower mu street or endurance pads in the .40~.55 range, we would stick with a stock M/C. With high mu pads in the .65~.75 range, the 1" M/C starts to work better.

None of this mentions booster ratio. Everything else being equal, we recommend the booster with the lowest ratio possible for the best feel. Booster basically amplifies your pedal force input. More boost makes it harder for the driver to modulate than less boost.
Last option regarding boosters is to eliminate it entirely. Doesn't work with OEM M/C as you end up with too little hydraulic advantage. Rock hard pedal but dangerously high effort (>150lbs to lock). Boosterless will require going down to 1/2 to 5/8" M/C on most NA/NB race cars with race pads and big rotors.
We made it work with Tilton pedals which are themselves, adjustable. That conversion not for the faint of heart. We only did it to allow a straight cage tube extending from the triangulation point on door hoop to shock tower. Keith Tanner has a great post on m.net listing booster ratios. Highly recommend you read his post if you plan on mix and matching M/C's and boosters. https://forum.miata.net/vb/showthread.php?t=363284

 

emilio,

so for those of us with cars that came with sport rear's and 11" kits, are you saying, potentially, to go with nb1 rear calipers/sport rotors AND 11.75" kits - or just the rear calipers?

With the rear caliper change, will that effect the pedal leverage much? Otherwise I'm still considering the 1" mc...

is the 929 1" mc still the one to get, or the wildwood 1" mc better?

 

The issue is that Sport Brakes with the same race compound front and rear tend to have too much rear brake bias even with stock rotors. Adding our 11" up front won't improve that enough in our experience. You'll need to run a higher mu (friction coefficient) front pad than rear, see if that works. If not, swap to NA8, NB1 rear calipers on your Sport rear rotors. That usually works in conjunction with an 11" front with ~3.00 piston area like our Boxmount kit.

If you need maximum brake torque and thermal capacity, over 250whp street or 200whp track, wait for our 11.75 Superlite kit.

We run the Wilwood 1" M/C on all our cars. Our 1" M/C kit is being updated and should cost a bit less when you see it again. Might not be listed on our site as of today.

Smaller rear caliper piston of NA8/NB1 don't change pedal feel a bunch. You'll feel the difference, but its slight. Not nearly the difference you feel with the 1" M/C. If you are running race pads, the 1" M/C is a must have upgrade for feel.

 

I'll be due for front caliper rebuild/replacement for my still stock-powered but eventual ST5/6 car. With the relative low cost of entry of the 11" kit, readily available and cost effective rotors, and cheaper pad shape than OE shaped pads, I feel like this is a no brainer for longevity/serviceability sake. Am I correct in that, or is any BBK still considered overkill for an eventual 150-ish whp build when stock hardware works "just fine?" Currently using Hawk DTC-60 fronts and DTC-30 non-sport rears.

I do currently have my stock setup ducted with the Singular ducts, but it sounds like your design will be centralized to the hub/inner rotor, so that seems like a slight upgrade in itself as well. I know the "upgraded" brakes in NASA's class calculation gets a 0.2 penalty, so is the greater thermal capacity and better ducting, along with price point and serviceability like I mentioned above, worth the small penalty? That 0.2 penalty results in approx. 2 less peak horsepower for a 2300 lb car.

 

OEM brakes can work fine at <150whp. Supermiata SSC is a 2300#, 140whp car with no downforce on 225/45 RS4's. Most run Sport front (10.6") and NB1/NA8 rears with something equivalent to R12/R10 pads. Plenty of brakes and most SSC's don't have ducts. Only a few have a 1" M/C.
The 7112 plate in the DL4 is about the same pad volume as OE Sport, so no gain there. A bit more torque from the larger rotor but mostly a big weight reduction and much faster pad swaps. For ST6, I'd stay OEM. For ST5, I might spring for an 11" BBK. Dan's (Doward) ST5 NB1 runs an 11.75 TSE Dynapro kit IIRC.

Race car rules sometime override efficiency. In the old PT days, we ran OEM sway bars and end links with monster springs on our NB1 to free up precious point for the NB1 VICS intake manifold on our NB2 engine.

 

Thank you Emilio. I very much appreciate your experienced racer answer as opposed to most vendors who would simply say that their product is superior to all and that buying it will always be the best option.

It's so awesome to you guys continuing to develop top-notch parts for NA/NBs. I'm looking forward to seeing the success of this kit.

 

Is anyone making/printing, or has anyone adapted a Corvette or Porsche brake cooling air deflector to fit the front A arms?
Would love to see one adapted or printed, something tells me they might be a consumable on curbs?