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Doc
12-01-2005, 11:11 AM
As you can see from the other threads I've been doing a lot of thinking and research regarding front brake options. I decided to compile a list of some of the common options to aid in planning.

First off, DISCS. A larger disc is effectively a larger lever arm for the brakes to act against. I made a little table to compare the expected effectiveness of larger rotors. The brake pad rides towards the outside of the disc, but the force is spread over a wide band of contact, not just the outermost edge. In my calculations I assumed that the pad was 1.5" wide. Therefore the center of the pad (or 0.75" in from the edge of the disc) was where the force would be concentrated. This may not be 100% accurate but it should yield a good comparison as long as it is consistently applied.

Keep in mind that this chart is Disc properties ONLY:

Disc OD: Effective Radius: Theoretical improvement:

10" 4.25" 0% (OEM size)
11" 4.75" 12% (Standard B-body brakes; also used in some aftermarket kits)
12" 5.25" 24% (B-Body heavy duty rotor such as IROC or "police brakes"; also aftermarket kits offered by Baer, Wilwood, etc.)
13" 5.75" 35% (Largest aftermarket kit offered by BAER)
14" 6.25" 47% (Listed for custom purposes only)

....as you can see the trend is roughly 12% per inch.


Now for the calipers. The effectiveness of a caliper is based on the area of the piston(s). In the case of 4-piston calipers where there are two pistons on each side of the disc, only the area of one side of the caliper counts.

Caliper: Piston Dia & Count: Effective Area: Improvement:

Stock GN 1x 2.48" 4.8 sq. in. 0%
OEM- Oversize* 1x 2.75" 5.9 sq. in. 20%
Wilwood Dynalite 4x 1.75" 4.8 sq. in. 0%
S-10 Blazer 2x 40mm 3.9 sq. in. -19% (performance LOSS!)
PBR Caliper (Baer)** 2x 38mm 3.5 sq. in. -27% (again, LOSS!)

*"OEM-Oversize" is the OEM style aftermarket calipers such as those made by Wilwood and US Brakes. They are the same style as the stock GM calipers but they have a larger piston. These calipers would be a direct swap for factory GN calipers. This is also the same piston size as the "big brake" option for the B body GM cars. If you use the "Police Package" brakes from a Caprice those also have a single 2.75" piston. However, the B Body calipers are a different style than the GN caliper; to use the B body calipers you have to use B body spindles.


**The often lauded Camaro/Corvette calipers are also 2x 38mm like the PBR, etc.


The Caliper info is interesting because it seems that the only real upgrade to be had here is the OEM style oversize calipers. That's interesting becasue they are among the most inexpensive as well.

These numbers are multiplied together when considering a full conversion. So, some examples might be:

B body swap with IROC rotors and Police Package Calipers 1.24 x 1.20 = 49% improvement

Wilwood aftermarket kit (12" rotors and Dynalite caliper)= 1.24 x 1.00 = 24% improvement

10" Discs + Overize OEM style caliper such as the US Brake = 1.00 x 1.20 = 20% improvement

12" Discs + Blazer calipers = 1.24 x 0.81 = Almost no improvement

13" Discs + PBR calipers (Baer kit) = 1.35 x 0.73 = 2% LOSS! (Perhaps this is why Baer recommends swapping in a smaller bore master cylinder???)

Of course, this information is only part of the puzzle. Larger discs are also good for better cooling. So, even though the above example of the Baer kit would respond in a small LOSS in braking power, the 13" discs in that kit WOULD have much better fading resistance compared to stock. For autocross or road course driving they would be far superior to stock due to this.

Likewise, some calipers are stiffer than others. My comparison was of clamping pressure only. Perhaps some of the calipers are stiffer than others, which might offer a benefit that I did not take into account.

kenmosher
12-01-2005, 01:29 PM
Great stuff! Sticky!

Turbobuick
12-01-2005, 04:05 PM
Doc,
I think you are looking at the caliper sizes a little wrong. The size of the piston does not necessarily determine the performance of a caliper. The absolute biggest determining factor is going to brake surface area, IE the size of the pad. How the caliper distrubtes clamping force on the back of the caliper, single v.s. dual v.s. four piston calipers. A dual piston PBR caliper has a MUCH larger brake pad surface area and the caliper distributes the clamping force MUCH more evenly over the rear of the pad than a stock caliper. Same thing is true for the 11" S10 balzer upgrade. That brake upgrade is going to be significantly better than the stock brakes because it has a significantly larger brake surface with calipers that distribute pressure more evenly. It's not how hard the caliper clamps but how much surface area and how it is distributed that make the difference.

There are other factors that play into this also including how the caliper is mounted. The PBR is a full floating design and not a fixed mount design like the Dynalite in the Wilwood kit. I don't know enough about this stuff but I do know that is important in a road race/ street car brake setup.

Just my point of view, thanks for compiling the info though and it is good for comparing the differences.

Doc
12-01-2005, 05:24 PM
That is only partially true...

Brakes work based on friction. The frictional force between two sliding objects is based ONLY on TWO factors:

1. The Normal Force, or in Layman's terms, the force holding the two objects together. (In our case this is the clamping force exerted by the caliper onto the pads and rotor)

2. The coefficient of friction, which is a property of the materials that the sliding objects are made of. (In our case, this has to do with the materials used for the rotor and the brake pads). When you swap to "high grip" brake pads you are changing this property.

You can look up this equation in any basic Physics textbook. Note that the AREA of the contact (for example, the size of the pads) does not enter into this equation at all. I know it is counter-intuitive, but it is true.

Now then, larger brake pads are going to be more DURABLE than smaller ones, becasue the energy lost to friction is spread out over a larger area. So yes, in a way larger brake pads and larger numbers of pistons are better in some regards: durability and resistance to heat-based fade and damage.

But for RAW BRAKING POWER ONLY, area is king.

Of course, all of the above assumes that the caliper is stiff enough to actually apply the force to the pads. If you have a caliper with giant pistons but it is too flexible to properly clamp the pads then you will never realize the benefits of all that area. As I noted at the end of my original post, the stiffness of the calipers might affect the results. I have no way to measure the stiffness of the various calipers discussed, so I can't really comment on that. However, it is something to think about.

Turbobuick
12-01-2005, 05:49 PM
I'm not sure were you are going with this but in all the disc brake arrangements you have listed above the 13" rotors with PBR calipers are going to be FAR superior to anything else you have listed, and I know this from experience. "Raw braking power" is going to be determined by many factors other than piston size. Pad size, fluid dynamics, rotor size, heat, caliper size, all contribute greatly to the overall design and function. MC bore diameter has nothing to do with this and has to do with pedal travel and feel.

I'm no expert in braking, by far, but I have run the 1LE brakes, wilwoods and the 13" PBR brakes on a race track (road racing and drag racing) and will take a 13" brake with PBR caliper over the others listed, any day of the week and especially on Sunday!

Doc
12-01-2005, 07:51 PM
Master Cylinder bore has a large effect on braking power.

If you get a smaller bore master cylinder, then you are increasing the pressure generated in the brake lines with the same amount of pedal effort. That is going to improve the caliper grip force by the same amount.

A 10% smaller (area) master cylinder would be an EXACT EQUIVALENT to 10% larger (area) pistons in all your brakes. Of course, there is a practical limit: too small a MC and you won't have enough fluid displaced to properly brake.

Read any basic book on Hydraulics if that explanation isn't clear.

I think that the success of the PBR setup is that the PBR calipers are probably stiffer than OEM (and others too?). Therefore, they are capable of applying a greater force DESPITE the fact that they have a smaller active area than some of the other choices.

Again, I hate to beat a dead horse but I've clearly stated that none of this takes stiffness into account.

Doc
12-02-2005, 10:10 PM
Hey everyone, I made some edits to my original post.

I visited the local O'Reily today and examined a few different calipers. It turns out that the "B Body" heavy duty caliper (e.g. 12" Caprice brakes) has a 2.75" piston. I THINK that this is the same caliper used on 3/4 ton trucks during the 70's as well....I haven't compared them side by side, but it looks very similar.

This means that a properly done 12" B-body swap is going to have very, very, good performance: nearly a 50% upgrade!

The B body brake parts are very cheap. O'Reily quoted me $15 for a caliper ($5 core) and $26 for an IROC brake disc. The downside, of course, is that you have to drop a few hundred $$$ on control arms in order to use the B-Body parts....and even then you still need spindles.

Wilwood (and perhaps others) make an aftermarket caliper that is a drop-in replacement for the B body style. The piston diameter is the same, but Wilwood claims their caliper is significantly lighter than OEM, and that it is much stiffer as well. Unfortunatley, these are fairly expensive; $125 each from Summit.

buddiiee
12-06-2005, 06:49 AM
i see.. thats good stuff but.. my stock brakes work just fine ;)

if your brakes dont work that good, try improving the rears, with bigger cylinders. and ive also heard, from i think it was ken mosher, but dont quote me on that..that you can take the two larger shoes, and put them onto one side, then buy another set, and use those two large shoes on the other side. then throw some aluminum drums on there. im guessing the aluminum drums keep things a tad cooler, as i know aluminum gives up its heat really quickly, and that has to be good news for break shoes. if you run this option, and everything else is tuned to where its supposed to be, you should be just fine. if youre trying to boost at the line, and your brakes cant hold ya, do a line lock or trans brake. but, for as hard as i drive my gn, (which is kinda hard) my brakes work just fine.

kenmosher
12-06-2005, 11:32 AM
Actually, I don't endorse the two long shoe rear brakes mod ... my thought has always been that the longer shoe distorts more (much to Doc's point with the front caliper stiffness discussion).

I run the larger rear cylinders and soft compound organic rear shoes (again, to Doc's point about friction coefficient ... the cheapy shoes won't wear as long, but usually have better friction).

So ... anyway, I think the discussion above was launched by the thought of running discs on all four corners, so the rears are probably off point.

Dave Burchfiel
01-20-2006, 07:48 PM
Ok! I've been reading about brakes and I'm still not sure what to do. Since 1987 my brakes have been terrible. as far as I'm concerned its the worst thing about the GN. Fairly early (when my accumulator failed on the powermaster) converted to vacuum brakes. I've bled them, replaced the master cylinder and vacuum acumulator twice, replaced the shoes with soft compounds, replaced the pads with semi metalic (that may have even made them worse) and I'm surprised in the 140,000 miles I've driven the car I haven't wrecked it (at least not because of the brakes). The pedal travel is way too long before the brakes engage; yet not spongy. (there is no air in the system) I can't lock the brakes if I stand on the pedal with both feet. Once in a while they might give a hint of a lock up. Sometimes but not often the pedal is just hard as a rock with almost no braking. Combination valve problems?

I'm thinking of going to 13" baer brakes in the front and 12" in the rear but after reading the forum I'm hesitant. Doc states that pad area has no affect on braking and it's strictly force and cf. I remember that from physics yet I think more is going on or why would we run nice fat tires since area (contact patch) wouldn't change the traction.

Doc
01-30-2006, 04:37 PM
Dave,

Tires are a little different than brakes. The reason is that tire contact isn't strictly limited to friction alone. There is the "stickiness" of the rubber, and also the fact that the rubber is soft and conforms to the rough road surface. Friction does not account for this kind of behavior. Consequently, larger tires have some non-friction advantages. (They also have better heat handling characteristics). Don't forget that one of the major advantages of drag tires is not just the size, but also the wrinklewall design.


Back to brakes: Personally, I would not use the BAER kits. This is because in my opinion they are dreadfully expensive. I admit that I have not used them personally, but I simply cannot see that their braking performance would be THAT good.

A few things to consider, assuming that your brake system is properly bled, etc.

1. Generally, softer pads (organics) give better braking than some of the long-wearing pad designs. I would consider using a soft pad, or a pad specifically designed for performance braking. You probably won't find the latter at a typical auto parts store. Try Summit.

2. Make sure you have a check valve in the vacuum hose that goes to your power booster.

3. If you are going to consider upgrade parts:

I would first try using the US Brake or Wilwood OEM style but oversize calipers. They are quite inexpensive, and will yield a solid 20% in clamping force. That's probably your best bang for the buck.

If that's not good enough, then I would consider the Wilwood kit if you want an "easy to do" swap. Everything is in the kit, and it should be far less expensive than the Baer kit. If you'd rather take a more hands-on approach, then I'd go with the 12" swap using GM parts, while utlizing the oversize OEM style calipers mentioned above.

4. Don't forget about your rear brakes. You can always swap in larger pistons back there as well.

Dave Burchfiel
01-31-2006, 08:22 PM
Doc, thanks for the input. I have the check valve and the brakes are properly bled etc. I've been doing a lot of research on this site and others.
and I've found I'm not the only one who has converted to vacuum brakes who's still having problems. The following is a post and reply from Hydratech. I've ordered a hydraboost unit (not cheap) and I'll let everyone know the results when it's installed. Probably be a few weeks. Even if it performs as advertised I'll be upgrading to 12" front and putting discs on the rear sometime in the future.

I have a Buick GN that has terrible brakes. I converted from the powermaster to vacuum brakes about 14 years ago. I'm running 16x8" wheels with 245/50 tires. I have three problems; the first was present with the powermaster and that is no matter what I can't lock the brakes. the 2nd and third are only with the vacuum conversion. The pedal travels a long way before the brakes even start to engage and on occasion, usually when the car is cold the brakes have no power assist at all and standing on the brakes with both feet barely stops the car from a slow roll.
I've changed the master cylinder three times and the booster twice. The vacuum canister doesn't leak, the lines are all good and have been replaced several times. I'm stumped. Could the combination valve be causing some of the problems. I guess the master cylinder has a "quick take up spool" (not sure what that is) but I think it stops the front brakes from applying before the rear drums have begun to engage. The master is from a 1987 Monte Carlo SS. The rest of the brakes are stock except for semi-metalic pads and soft compound shoes.

I'm pretty certain i'm going to convert to hydraboost. Will this take care of my problems? Do I need a different master cylinder? I'm eventually converting to Baer brakes. 13" front 12" rear. Are thera any special considerations for the hydraboost kit with that setup?

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Hydratech
Site Admin


Joined: 24 Jan 2005
Posts: 149
Location: MotorCity
Posted: Mon Jan 30, 2006 12:02 pm Post subject:

--------------------------------------------------------------------------------

Hi Dave - Yes, our GN systems will definitely knock your socks off with the power that they can produce! (guaranteed in writing or your money back in full). These systems are also totally consistent, with the same brake response at all times - whether it's cold or hot, whether you're running ten mph or 120 mph. Reliability is also second to none, which is why GM has decided to start installing these types of systems on most all of their truck lineup these days.

It sounds like your vac setup isn't running all that well due to the SFI Turbo V6 not particularly pulling enough vacuum, especially when cold. The factory G-body QTU (quick take up) design 3 piston master cylinders are pesky, as the valving inside usually doesn't work right - this could also be a factor in your situation. I am actually currently running a dead stock '86 442 (55k original miles), and have installed one of our hydraulic brake assist systems in this vehicle, (what a difference in braking with no other changes!), to find that I can't wait to get rid of the stock QTU design mc. Depending on just how fast and hard you hit the brakes, the pesky QTU design MC will just simply drive me nuts in use per inconsistent braking actions. I have swapped out the MC with a brand new AC Delco unit in thinking that maybe the original MC was tired, just to find that there was no improvement = I now recommend against the use of these types of master cylinders, as the idea seemed to be great "on paper", though just doesn't seem to really work properly in actual use. GM has also discontinued use of these types of MC's in many various applications (where they were used for years), apparently for the same reasons why I don't like these things. My experience tells me that your MC is most likely suffering an internal check valve problem, to where the QTU function isn't working correctly to cause your low pedal complaints. The idea behind these designs is this: When you first hit the brakes, the high volume oversized rearmost piston is *supposed* to take up any slack in the system first, then a check valve kicks in to shut off the QTU function and then follow through with the forward two conventional smaller MC pistons to produce the pressures the brakes need. As you can imagine, this action is subject to various little metering / check valves inside of this type of MC working properly, which can malfunction with even the slightest little piece of dirt or wear. If the internal valves aren't working correctly, you can experience so many different problems that it would even be quite a challenge to list all the possible symptoms. Again, this is exactly why I don't like these designs, and generally recommend against their use...

QUOTE: I'm pretty certain i'm going to convert to hydraboost. Will this take care of my problems?

REPLY: YES - satisfaction guaranteed of your money back in full.

QUOTE: Do I need a different master cylinder?

REPLY: Yes - the QTU design oversized rear register of the '87 Monte SS MC (the rear part that actually fits into the booster) will not fit the "mouth" of the replacement hydraulic assist unit, so a conventional 2 piston design mc will be needed. We have bored the assist units open larger to fit the factory G body QTU MC's in testing, (like my 442), to find that even though we *can* make them fit, that we simply just out and out do not recommend the use of this type of MC. To that end, there are quite a few various factory type of MC's and a host of aftermarket MC's that you could consider installing (as the assist unit is designed to accept most all '77 and newer design GM non-QTU power brake master cylinders - you could even use a '96-'02 Z-28 or '97-'02 C5 Corvette plastic / aluminum if you wanted to). The target bore size should be 1 1/8", though the 1" bore versions will work OK too.

QUOTE: I'm eventually converting to Baer brakes. 13" front 12" rear. Are thera any special considerations for the hydraboost kit with that setup?

REPLY: Even though the booster is hydraulic, all of the usual conventional wisdoms still apply from the MC forward. To that end, there really isn't anything you would particularly have to do differently because of having a hydraulic brake assist unit (as opposed to a vac booster).
_________________

POWERBRAKEBOB
03-01-2008, 07:31 PM
Interesting to see that all those High Perf calipers always show less stopping power over stock. The real problem with the g.N. is that weak Powermaster booster system. Now, after 20 years the electric motor pumps are all failing. Those pumps had to use phenolic vanes inside to be able to run without galling, since brake fluid is not a high pressure lubricant. The other problem with the pumps, is when the seal leaks between the pump and the windings. When the elec. side fills with brake fluid, it shorts out. Buick never used the standard Regal vacuum booster on their supercharged cars. Vacuum boosters need vacuum, (20") and a 231 ci. motor with a turbo, cruising along in overdrive, has very little. The G.N. is a heavy fast car, and was built when G.M. was downsizing cars. They used all S10 brakes on the fast car. Not good. We have been converting the Powermasters to brand new Hydroboost units. They bolt right on, and use the same pedal as the powermaster. We use stainless braided hose to connect to hte pump, and box. The master is replaceable, easily, and we them in aluminum. Guys are reporting being able to hold up to 22lbs of boost, with their foot on the brake. The car stops like any new car, at any speed, with less rotor heat. Hydroboosts run off of the p/s pump, and need no vacuum, and no electricity. They can last up to 200,000 miles with just an occasional p/s fluid replacement.

turbo nasty
07-23-2008, 11:07 AM
Vacuum boosters need vacuum, (20") and a 231 ci. motor with a turbo, cruising along in overdrive, has very little. The G.N. is a heavy fast car, and was built when G.M. was downsizing cars.

HB systems work but lets look at some basic facts here.

Explain why the vac brake system was factory equipped on the 89 Turbo Trans Am that had the SAME turbo V6 engine and 2004r OD trans as the GN / turbo regals????

Furthermore the TTA was used as a Pace car and was definitely in overdrive doing considerable speeds while performing this task and stopped just fine.

Keller
07-23-2008, 01:07 PM
You may forget that the TTA had four wheel disc brakes, and their front rotors were larger than those of the G-body fronts. The 16" wheels were required to fit their rotors. The swept area is much larger than the TRs! The rear brakes on our cars are about as good as Fred Flintstone and his feet at high speed.

This is like comparing apples and cumquats. the 1LE package on the TTA is light years better than the 1960's era braking system (sans Powermaster) in the TRs.

turbofish38
07-24-2008, 04:35 PM
I never found PBBob to have much credibilty as far as any turbo'd car goes. Just check out his threads over on the other boards. As far as I'm concerned he is a gypsy selling snake oil.

I dont think the matter is so much the type of booster but the size and capacity of the brake system in general. I've done some wild stunts with the stock brakes on my 455 Regal and equally wierder things with the PM and vacuum brakes on the GN. I would say you're sitting good if you have a firm brake pedal and can lock up the fronts at will reguardless of the calipers and how sticky the tires are.

Funny thing how you never hear anyone complain about the lack of ABS on these cars. In other words, just like there is a technique to making our cars go fast there is also a technique to slowing them down....fast.

turbo nasty
07-24-2008, 06:49 PM
You may forget that the TTA had four wheel disc brakes, and their front rotors were larger than those of the G-body fronts. The 16" wheels were required to fit their rotors. The swept area is much larger than the TRs! The rear brakes on our cars are about as good as Fred Flintstone and his feet at high speed.

This is like comparing apples and cumquats. the 1LE package on the TTA is light years better than the 1960's era braking system (sans Powermaster) in the TRs.

Lets not get confused here PB Bob is stating that the turbo V6 does not pull enough vac for the vac brakes to work properly.
The TTA with 1LE, larger disc, 4 discs or whatever is besides the point. And yes the brake torque from the larger rotors on the TTA is way better than the G Bodys not doubting that a bit and that fact never came under question or scrutiny....thats not the point!

Your saying that since the TTA had bigger rotors and the 1LE package is the reason the VAC brake system works on the TTA and you cant compare the 2 since the turbo regals brakes are 60's tech.
I guess the N/A engines in the GTA's and other equally brake equppied N/A powered TA's that pull vac more than the no vac pulling Turbo v6 stop 100 foot shorter than the TTA.
Its not a question of which car is better equipped from the factory brake wise i'm talking the engine ability to pull vac and the vac brakes ability to work.
I.e- PB Bob says the Turbo V6 doesnt have the vac to support a vac brake system.
I saying the TTA has it and if it would not pull enough vac I dont car if you had 14" brakes its not gonna stop properly.
My GN has the swap and I have not had one downside and can hold the exact same boost as with the PM. I have to admit i was nervous on the vac brakes ability tio hold boost but was pleasently surprised that it held the same amount.
MHO FWIW

Keller
07-24-2008, 07:38 PM
I believe the only issue where brake "holding" with the TR's is really at issue is at the line, where someone may be on the pedal for a long time. A good booster should be all you need to hold them awhile. Otherwise, they should do just as well as a Powermaster.

Tdog
07-26-2008, 08:13 PM
Dave: Did you ever install the Hydraboost unit? The accumulator failed again on my Powermaster unit and I just can't see putting another $200 into it. I already have the B body spindles and the 1LE rotors. I also have the large wheel cylinders in the back, but would like to install rear disks also. My car tends to nosedive with the additional braking force up front. The Hydraboost costs much more that the vacuum assist, but seems to me that it would be more consistent. I don't mind spending more for a better system. We spend lots to make them go fast. I wanted to get an opinion from someone that has the Hydraboost to see if they are happy with it. Thanks for the info guys, this discussion has been interesting.

joe_schindler
10-01-2009, 03:03 PM
Sorry; I’ve not looked over here in a while. Other sites are linking back to this; so:

As you can see from the other threads I've been doing a lot of thinking and research regarding front brake options. I decided to compile a list of some of the common options to aid in planning.

First off, DISCS. A larger disc is effectively a larger lever arm for the brakes to act against. I made a little table to compare the expected effectiveness of larger rotors. The brake pad rides towards the outside of the disc, but the force is spread over a wide band of contact, not just the outermost edge. In my calculations I assumed that the pad was 1.5" wide. Therefore the center of the pad (or 0.75" in from the edge of the disc) was where the force would be concentrated. This may not be 100% accurate but it should yield a good comparison as long as it is consistently applied.

Keep in mind that this chart is Disc properties ONLY:

Disc OD: Effective Radius: Theoretical improvement:

10" 4.25" 0% (OEM size)
11" 4.75" 12% (Standard B-body brakes; also used in some aftermarket kits)
12" 5.25" 24% (B-Body heavy duty rotor such as IROC or "police brakes"; also aftermarket kits offered by Baer, Wilwood, etc.)
13" 5.75" 35% (Largest aftermarket kit offered by BAER)
14" 6.25" 47% (Listed for custom purposes only)

....as you can see the trend is roughly 12% per inch.


Now for the calipers. The effectiveness of a caliper is based on the area of the piston(s). In the case of 4-piston calipers where there are two pistons on each side of the disc, only the area of one side of the caliper counts.

Caliper: Piston Dia & Count: Effective Area: Improvement:

Stock GN 1x 2.48" 4.8 sq. in. 0%
OEM- Oversize* 1x 2.75" 5.9 sq. in. 20%
Wilwood Dynalite 4x 1.75" 4.8 sq. in. 0%
S-10 Blazer 2x 40mm 3.9 sq. in. -19% (performance LOSS!)
PBR Caliper (Baer)** 2x 38mm 3.5 sq. in. -27% (again, LOSS!)

*"OEM-Oversize" is the OEM style aftermarket calipers such as those made by Wilwood and US Brakes. They are the same style as the stock GM calipers but they have a larger piston. These calipers would be a direct swap for factory GN calipers. This is also the same piston size as the "big brake" option for the B body GM cars. If you use the "Police Package" brakes from a Caprice those also have a single 2.75" piston. However, the B Body calipers are a different style than the GN caliper; to use the B body calipers you have to use B body spindles.


**The often lauded Camaro/Corvette calipers are also 2x 38mm like the PBR, etc.


The Caliper info is interesting because it seems that the only real upgrade to be had here is the OEM style oversize calipers. That's interesting becasue they are among the most inexpensive as well.

These numbers are multiplied together when considering a full conversion. So, some examples might be:

B body swap with IROC rotors and Police Package Calipers 1.24 x 1.20 = 49% improvement

Wilwood aftermarket kit (12" rotors and Dynalite caliper)= 1.24 x 1.00 = 24% improvement

10" Discs + Overize OEM style caliper such as the US Brake = 1.00 x 1.20 = 20% improvement

12" Discs + Blazer calipers = 1.24 x 0.81 = Almost no improvement

13" Discs + PBR calipers (Baer kit) = 1.35 x 0.73 = 2% LOSS! (Perhaps this is why Baer recommends swapping in a smaller bore master cylinder???)

Of course, this information is only part of the puzzle. Larger discs are also good for better cooling. So, even though the above example of the Baer kit would respond in a small LOSS in braking power, the 13" discs in that kit WOULD have much better fading resistance compared to stock. For autocross or road course driving they would be far superior to stock due to this.

Likewise, some calipers are stiffer than others. My comparison was of clamping pressure only. Perhaps some of the calipers are stiffer than others, which might offer a benefit that I did not take into account.

4 piston calipers don’t work off of 2 pistons. You get the clamping force of all 4 pistons; not just 2. Otherwise; there’d be little advantage to 4 piston calipers.

Rotor diameter does not help the braking system. Swept Area is what you’re looking for; and you usually get that from a larger rotor.

joe_schindler
10-01-2009, 03:04 PM
Doc,
I think you are looking at the caliper sizes a little wrong. The size of the piston does not necessarily determine the performance of a caliper. The absolute biggest determining factor is going to brake surface area, IE the size of the pad. How the caliper distrubtes clamping force on the back of the caliper, single v.s. dual v.s. four piston calipers. A dual piston PBR caliper has a MUCH larger brake pad surface area and the caliper distributes the clamping force MUCH more evenly over the rear of the pad than a stock caliper. Same thing is true for the 11" S10 balzer upgrade. That brake upgrade is going to be significantly better than the stock brakes because it has a significantly larger brake surface with calipers that distribute pressure more evenly. It's not how hard the caliper clamps but how much surface area and how it is distributed that make the difference.

There are other factors that play into this also including how the caliper is mounted. The PBR is a full floating design and not a fixed mount design like the Dynalite in the Wilwood kit. I don't know enough about this stuff but I do know that is important in a road race/ street car brake setup.

Just my point of view, thanks for compiling the info though and it is good for comparing the differences.

Swept Area.

joe_schindler
10-01-2009, 03:04 PM
That is only partially true...

Brakes work based on friction. The frictional force between two sliding objects is based ONLY on TWO factors:

1. The Normal Force, or in Layman's terms, the force holding the two objects together. (In our case this is the clamping force exerted by the caliper onto the pads and rotor)

2. The coefficient of friction, which is a property of the materials that the sliding objects are made of. (In our case, this has to do with the materials used for the rotor and the brake pads). When you swap to "high grip" brake pads you are changing this property.

You can look up this equation in any basic Physics textbook. Note that the AREA of the contact (for example, the size of the pads) does not enter into this equation at all. I know it is counter-intuitive, but it is true.

Now then, larger brake pads are going to be more DURABLE than smaller ones, becasue the energy lost to friction is spread out over a larger area. So yes, in a way larger brake pads and larger numbers of pistons are better in some regards: durability and resistance to heat-based fade and damage.

But for RAW BRAKING POWER ONLY, area is king.

Of course, all of the above assumes that the caliper is stiff enough to actually apply the force to the pads. If you have a caliper with giant pistons but it is too flexible to properly clamp the pads then you will never realize the benefits of all that area. As I noted at the end of my original post, the stiffness of the calipers might affect the results. I have no way to measure the stiffness of the various calipers discussed, so I can't really comment on that. However, it is something to think about.

Automotive brakes are simply a crude system for converting kinetic energy to heat. Too many people confuse a firm brake pedal with good brakes.

How efficiently the system works is dependent on swept area, friction coefficient of the pads/rotor, clamping force, and application force. It’s a system; not a magic wand.

cocarter1
11-19-2011, 10:39 PM
Cannot beat the hydroboost! Way more pressure at the master cylinder.
Conrad