944Hybrids: 924/944/968 and 928 V8 Conversions
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brakes & Master cylinders - summary of findings + misc ramblings Empty brakes & Master cylinders - summary of findings + misc ramblings

Post  gamman Thu Mar 11, 2010 11:11 am

There is a lot of M/C discussion on the other board.

Don't know if you want me to link to them or not.

Thread drift 1.a.background
I had an incident with my car on the weekend, and it was many fold.
CAR: stock 16V NA 944S brakes (upgraded to M474, but still way less than turbo brakes, with new rotors and minitex pads).
M/C: Stock
Pivot point: raised, don't know how much.

was going about 50-60mph

had to STAND on the brakes. Really didn't like it. Went to ditch for avoidance. Forgot to pump. Gravel on roads, but only on the sides.

won't race with this setup.

Back on thread:
MC manual thoughts:
The actuation of the MC and the clamping of calipers are 2 different things. I think of it like a turbo with spool up. You can get to 20psi with a manual boost controller, but you can also set "ramp up" time it takes to get there. I think of the calipers as the target psi (clamping force attainable) and the master cylinder as the "ramp". You can choose 1-100% brake force. Trouble is, if you race, or want to stop quickly (IE: kid in road/dog in road/cop in road), you need to get to 100% as fast as possible. This is partly responsible for short braking distance, as how long does it take to lift from throttle to brakes, to 100% on the calipers. Racers actually like getting 2-25% on the brake pedal, and like to modulate, so I understand liking that. However, my track also requires 2 points going from 120+mph to about 80. Required late braking as possible. The effort required by me, in the situation above, required as much braking or more than the track situation, in as fast a time possible. If one were to upgrade the brakes with lexus, or turbo or what have you, you would indeed have more force to exert on the braking situation. However, you are limited by traction. Tires and suspension. If your tires are crap (mine were my 215/225 all seasons) you will get bad braking. If you have nice sticky tires, you will get better braking, but also require more force (this I am not to sure how it works). this exercise ignores the thermal capacity of racing argument for now (I have faded/boiled enough brakes over the years to write a book on it).

So, if you have manual brakes, it may take -say 1 second to get to the 100% point. At 120mph, that is 2 miles a minute, or 176 feet per second. So, if you get a power braking system, that actuates the brakes faster by, say 0.5 seconds (maybe too twichy - I have no idea - I am speculating) the difference will be 88 feet. Or put another way, every 1/10 of a second faster that the brakes get to 100%, is 17.6 feet. This assumes all other things being equal, apart from the m/c actuator levels. I guess what I am saying here, is that I don't think that my spindly legs can push the manual brakes as fast as a power setup. I would bet that it is easy 0.5 of a second to do the 100lb squat on the brake pedal. = 88 feet.
Of course, you hardly ever get to 120mph, but on the street, 60mph is attainable (no street racing please), divide by 2, to get to 60mph.
1/10 = 8.8 feet
1 second = 88 feet
1/2 second = 44 feet

Anyway, on the other board, search abs or brakes, and there are about 3 threads on this topic.
Electric MC - expensive - few who use it like it. Expuppy had a failure, but it was due to routing of lines too close to the headers, and that was on the track racing. There was another guy (actually in my home province in Canada!) that has a electric 84 car, and he had fade, but I can't recall why (fell asleep last nite on computer). Will edit, when i find out why again. System has 10 stops in reserve.
Hydroboost - good option - I hate ford mustang brakes, and can't stomach putting this on my car. I may try it. System has 3 stops in reserve.
Manual - Wilwood/Tildon single/dual. Racers use this, so it obviously works. I just think that the stopping panic distance will be longer. Would actually be solid and modulateable on the track, and good for nose dive turn in, without actually applying much clamping force.
Manual - stock with raised pin. Some racers use this (600hp man). I can't believe it, but he does, but he also has upgraded front/back calipers and rotors, with the right pads, suspension and driving technique, which makes a huge difference.

Other notes:
the "wilwood" rennbay setup, is a nice street, autox and barely a track setup. I got the codes from cfg, and on the wilwood site, it even says these calipers are for light duty track. I wish the stuff were clearly explained on the rennbay site. Wilwood makes so many better calipers for racing, I wish rennbay would offer upgrades on the calipers, and I could have been done by now. Thank goodness I found that out, I knew my intuition was telling me something. I don't know what part #'s Expuppy is using, but he likes his setup. He said he paid around 700 for his calipers, which means that they aren't the rennbay calipers.

pads make a huge difference. Hawk HPS and HP+ pads are not road race pads. Well, the HP+ can survive the track, but there are WAY better, non-corrosive options out there. We heat tested my calipers on my 3100lb subaru 265, with ducts and 1 cooling down lap, and the pit entrance, and they were 900'. I went to a carbotech XP10 pad, with a 1400' limit, and they would fade on lap 5-6, with agressive use. I can handle that. As I can only do 6-7 laps in a session anyway.

driving technique makes a difference in road racing brake survival. Rookies over brake like crazy, and solve it by accelerating out. I know, I have done the last 4-5 years like this, and gone through stock sets of brakes like crazy. In one year, upgraded a 09 car's brakes to 3 different setups. In the end, air ducts and race pads and a proper suspension setup (for weight transfer) is all that was required.

large brakes and calipers make a difference only in thermal capacity and dissipation of heat. If you think about it this way, if you have a 17" rotor and brake (from a semi/corvette or what have you ), you think you would stop from 60 in 10 feet right? Well, what is the axle, hub and all that brake stuff connected to the ground? Tires. If you lock up, you have reached the traction differential of what the tires can slow you down at (or transfer to the ground). Abs (if you have it) will kick in. It is the ability to repeatedly do it, that the larger brakes gain (thermal capacity before heat sink). There is some ability to clamp harder, yes, but with bad street tires, the gain is almost immeasurable, I bet. It is kind of the reverse of the LSD in the rear arguement. If you break axles with Rcomps, go to a street tire, and I bet you break less axles. Moving the fuse is what it is called.
now if you agree with 4, then you move to a racy/stick Rcomp. Then there are 2 ways of thoughts. The tires will be wider, so there will be more rolling resistance (brakeing force off throttle) and there will be also able to carry more speed on the corner, so less braking is required (120 down to 80 vs 70 or 60 for street tires), so you actually require less brakes. However, if you have Rcomps, then you will be trail braking, which extends the duration of braking to say 3 seconds vs 2 seconds. The other thought is, the tires allow for more force to be transmitted to the ground, so then you need more clamping force, or could use more clamping force. This is one where I don't know. My problem was over braking. I went from a 60 UTQG rcomp (RA1/MPSC) to a 180 UTQG (Khumo XS) and 235 to 255. I found I was getting less fade/problems with less sticky tires, but was braking the same speeds roughly. Then I started trail braking, and could tell the thermal capacity was decreasing, but I was still learingin.

Thats it for now.

I am still uncertain what I want to do with my situation. I have put my car up for sale,and cancelled another transaction due to my weekend off roading experience.

I think it was more my tires and setup that caused the problem. I also think that electric MC may be more to my liking, even though it does run hydroboost (I think - I am still researching the ins and outs and will post with my summary results).


Posts : 112
Join date : 2010-01-12
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Post  Vorsche944 Fri Mar 12, 2010 11:19 am


Sorry to hear about the scary situation. I had the same thing happen when we first took my car out with just manual brakes, and I have a Turbo with calipers. Was going about 40 and tried to stop quickly for a stop sign, had everything I could on the break and she just did not stop like I wanted to. Thus we researched the options and went with the Hydroboost and the difference is dramatic. I have had a few times already just driving in town and having to avoid the idiots that pull out in front of you. She stops on a dime, stops clean, with force and under control.

Hope you get the situation worked out.

Posts : 146
Join date : 2009-06-09
Location : Arlington, Texas 76012


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Post  Dawgz83948 Fri Mar 12, 2010 11:39 am

Ya my BMW hydroboost worked a lot better than manual brakes. I'm going to the dual setup from Tilton because I want to get rid of the accessory tree and maybe make room for a S/C, wither way I want to get rid of my PS pump. So I'll have my BMW system for sale pretty soon.

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Join date : 2009-06-08
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