BrakeExpert

Hi. This is about the front brake upgrade using the "Accord/CL" calipers. This is the 17CL16VN caliper that goes over an 11.8" rotor, found on 99-03 CLs and later model Accords. I'll refer to it as the CL caliper, cause all CLs had it, and only some Accords did. I did some bigger brakes for someone who wanted this bigger caliper. It uses a pad of almost the same shape, but about 50% more in total area. It can work with the factory front S2000 disc, and bolts onto the knuckles. The caliper's piston is 2.25" compared to the 2" front S2k caliper piston. I've heard from some people that although this is a great upgrade, the fade resistance doesn't increase a whole lot with the heavier caliper. So, I figured how to mount thicker discs on. These would be from the 1999 Acura RL. They are 28mm thick and about 3lbs heavier per side. These rotors are taller and although they bolt onto the S2000's hub, the rotor does not clear the caliper bracket from the S2k or the CL. So the caliper bracket needs to be machined. It has to have the contact surface milled, roughly 7mm. I know this sounds like a lot, but remember that these are forged iron, they are very strong. And because the stock brackets did not use all of the threaded holes, when mounted, this new setup has almost the exact same number of rotations of threaded bracket to use. I removed as little material as possible, and though the bracket is not as thick, it is in fact less than half the material, and I do not feel this reduction in stiffness is enough to allow for any added caliper bracket flex or the potential for cracks or damage during operation. I realize some people will hate this idea because it does remove material, but it is safe. Here is a picture:



The S2k front knuckle and hub is an oddball compared to most Hondas, the rotors are shorter and the centerbore is the only one with a 70.1mm for the rotor but the "mid size" for the three diameters of the actual hub. That centerbore restricts rotor choices, so the only 11.8" to fit is the 98-04 RL's front disc.

TrackStar

Nice work. Are there any stock Honda caliper/rotor upgrades for the rear?

ZDan

(2/2.25)^2 => 26.5% more piston area up front, which will significantly increase front braking bias. If the stock bias is 70/30 under max braking, it will become more like 75/25. That is in the "safe" direction (less oversteer while trail-braking), and I suppose that the ABS would take care of the bias issue under maximum braking.

Another issue is that you will have increased pedal travel and decreased pedal force for a given level of braking.

For *me*, I wouldn't consider this mod because:
1. I don't have ABS and wouldn't want my braking bias to be moved that much to the front
2. With the pads I'm using there's plenty of decel at low levels of force at the pedal, with minimal pedal travel, wouldn't want to increas pedal travel or reduce pedal force
3. wouldn't want to increase unsprung weight
4. I don't have any issues with the stock system, it works fine for my usage (maximum ~20 minute sessions on track, and time trails).
5. Don't want to decrease oversteer/increase understeer under trail-braking

Regarding the structural ramifications of machining away 7mm of bracket (which may be forged steel, it certainly isn't forged iron!), properly designed structural components (which OEM will be) will have appropriate strength levels, whatever the material used. So it doesn't matter if the component is steel, aluminum, balsa wood, or boron, removing any of it may very well result in an unacceptable loss of strength!

If you have pictures or drawings or preferably CAD data on the part and the modification to it, I'd be happy to do a quick rough/dirty analysis.

daves221

if ur gunna use the money to get acura calipers, get nsx ones. I had a tl, and the guys on the acura side of things are doing acura legend caliper swaps, and nsx caliper swaps as they are dual pistons and both fit onto the stock tl/cl bracket and provide alot better stopping power than tl/cl calipers. tl/cl calipers are heavy, bulky, and ugly.

as for milling dwn the bracket, im with zdan on this one. As for now I'm sketched out by the idea, but I'm sure this will be tested and it's limits found. If the bracket still holds up with no sign of warping or cracking, then I think you've discovered something very worth while. However like zdan said again, some people may not want to mess with their braking bias if they race their cars. TL/CL's usually stop in straight lines as they are not being raced, but DD so having larger front braking bias is not that bad for them.

BrakeExpert

Honda-Acura are all the same. The NSX calipers can bolt to these brackets, but the 97+ NSX brackets cannot fit, and the 91 NSX brackets will use a smaller than stock diameter disc.

Milling the brackets has been done hundreds of times in the world of Hondas. From 4 lug type-R brakes, 4 lug S2k brakes, and CL calipers on CRXs, I've not heard of a single bracket ever failing.

I realize bias is a concern, and I don't mean to be rude, but aren't you bein a bit picky? I mean for optimizing on a track, if that bias chance is enough to affect your lap times, I will assume your car can't take the benefit of added front hear. With bigger brakes, I'd assume you have stuff like bigger, wider wheels, wide, sticky tires, a firmed up suspension, and upgraded pads, maybe race level or ceramic compounds. This particular picture has Hawk HPS performance pads. And yeah, I'd reccomend upping the rear pads too. Its just when I hear arguements like "I don't want to add unsprung weight", typically its coming from ricers who bought the smallest wheels possible cause someone told em less weight is better, ignoring tire compound and sidewall flex. I'm not saying thats you, but the feel I get is that no one wants to explore this area, and having driven an S2000, its brakes are good but have plenty of room for improvement, especially regarding fading those little front pads.

cenix

where would the legend dual-piston calipers fit into any one of these rotor options? what is possible with these calipers for an s2k? i haven't heard much about this conversion (for the s2k at least).

ZDan

That many people have done this and you haven't heard of a failure does not mean that structural integrity isn't compromised. But I did not and am not saying that it's *definitely* a problem. It *may* be.
Anyway, you said:
"It has to have the contact surface milled, roughly 7mm. I know this sounds like a lot, but remember that these are forged iron, they are very strong."

Surely they're cast or forged steel, not iron...
You can't say "it's made of strong material, therefore I can mill away a bunch of it and it won't matter." Properly designed structural OEM parts are going to be designed for adequate strength, stiffness, and fatigue life for minimum cost and weight. *Whatever* the material used, the part should have been designed to utilize the material's strength and stiffness while NOT being OVERbuilt. If you removed 7mm from the mating surface, you *drastically* reduced stiffness and increased operating stresses. This doesn't necessarily mean the part will definitely prematurely fail (though under extreme operating conditions I would NOT risk it), but for sure it isn't as stiff as it was and it's life has been reduced. If the usage profile doesn't include a lot of maximum braking, life might still be practically infinite. If the usage profile includes tracking the car, I would be concerned enough to do structural analysis before using brackets with so much material removed.

I don't think so. Speaking for *my* application (stock AP1 with nonfunctioning ABS), F/R braking bias being altered by +5/-5% would mean that when I lock the fronts, the rears are contributing a lot less. Hence, increased braking distances. With ABS working, this wouldn't be as much of an issue. But with or without ABS, with more front bias you will decrease oversteer/increase understeer in trail-braking. Which may or may not be desirable. For me, it's undesirable.

???

Hawk HPS pads are a significant DOWNgrade from OEM pads. Softer pedal and lower coefficient on the street, and unusable/downright DANGEROUS after a lap or less at the track. At least the one set I tried were. Worst pads EVER, *far* worse than OEM. HP+ do work quite well for me, though.

Sounds a lot like me. On my 240Z, I run 15x7s with 225/50-15s on the street, but my track setup is 14x7s with 225/50-14 Hoosiers. Sidewall flex is not a problem... Smaller diameter wheels/tires for the track gives some benefits (particularly for a street/track car) in addition to being lighter weight (which is of course a good thing for unsprung/rotational masses). Lower c.g. without altering suspension geometry. Lower gearing. Better braking response.

You really get the feeling that no one at S2ki wants to explore improved braking performance? PLENTY of us *have* explored this area, and many of us are quite able to get good braking performance at the track with the stock system with appropriate pads and fluid. I can still lock the brakes at the end of my run session, so this mod would have zero positives for me, but would bring a few negatives.
Where exactly are you fading those little front pads? If you are running HPS pads, actually I wouldn't be surprised if you were able to fade them driving stupidly deep into corners on twisty backroads on the street, but you shouldn't be fading OEM AP1 pads there. If you are, try HP+ pads, which in my experience have a very high coefficient of friction even stone cold. And if you're going to the track, there are plenty of pads to choose from.