I keep hearing this idea that BMW calipers add more heat vs stock caliper. I am not a physicist but any 2000 lb car going 60 mph with stock brakes is going to generate a certain amount of heat. Take the same exact car with smaller calipers (yes smaller) does it generate less heat? I don't think so. It is going to generate the same heat. The only thing that may change is the brake distance and time required to stop. Perhaps this extra couple of seconds it takes to stop allows more time to cool the brakes a tiny bit more, oh but your heating them longer. BMW calipers will add the same heat but faster. That is it. Other points are: the BMW rotors that these calipers were originally designed for are really close in diameter and thickness to our 914s. I'm sure someone will eventually post them. These BMW 320's were quite a bit heavier than our 914s as well. BMW used this combonation for 5 years it must have been a decent.

Check with a BMW repair shop or someone with direct knowledge...

Older BMWs tended to have too small of brakes for the specific vehicle....
and led to a lot of warped rotors.

My good friend and automotive shop owner made a lot of money replacing warped rotors on BMWs because of too much heat being generated and not being disapated quick enough to keep from causing the rotors to distort (warp)

forget the BMW calipers and do a nice M caliper upgrade with vented rotors, and no, you don't have to do a 5 lug conversion to make it happen.

Heat or no heat....I would prefer the brake calipers that give me the shortest stopping distance possible for a given application....

My $.02

Did you say that all in one breath? Joke.

It's a function of work/time. It only takes so much friction before the work done by the brakes defeats the work done by the tires and creates lockup. This is the maximum amount of work done before the brakes are useless. If your brakes are capable of doing this muchwork, then there is no need to upgrade. For a 914, the stock brakes are capable of locking the brakes, therefore there is no *NEED* to upgrade.

Reasons to upgrade the brakes.

1. You are aiming for a substantial unsprung weight reduction.

2. You go to wider tires, or something else that creates more fricton (operating at lower tire pressure, compounds etc)and can no longer lock the brakes at speed. (Need to do more work.)

3. Heat displacement. Larger brake bodies, or aluminum/ magnesium bodies offer the propensity to displace heat better. This is based on just a few variables. (More work= more friction= more heat.)

BMW brakes are an easy way to take advantage of points 1 and 3, but not 2. They aren't significantly larger to do more work. If they were, then it would be very easy to lockup the brakes, and would render the upgrade useless without a brake pressure adjusting unit.

These rules apply to ALL braking mechanisms, even my own be-all-end-all brakes. Someone get a link.

I did this conversion 6 years ago, 11,300 miles, 5 seasons of autocrossing. I have never experienced any warping or brake fade. The rotors look great, I run Ferrado street pads and measured the rotors for wear this past May at .003". I have Tons of pad left.

Soooo. Braking distance will not change with the caliper. The calipers that we have already do the maximum work to lock the brakes up at speed.

wow...
you need better pads.

pads are a wear item
I get 20-25 hours for a set of pads.

rock hard pads last for ever, but give up significant brake performance.

brant

So you don't think they do more work than the stock units if I am running wider tires? What pads would be a better compromise. I did get the thought but have taken no action. I heard the porterfields were good.

Can you lock 'em up with the the stockers? Or the BMWs? Whichever you have now. If you can, then there is no more work to be done. If it's too easy to lock, then there is too much brake work to be done.

Where's Andrew for all this. We can start bouncing the numbers. Wattage, and whatnot. Brakework can be converted to horsepower.

Pads are going to be important though. Better pads= more friction and worse heat conduction (good thing.)

I can lock them up with the BMWs, but it takes a little work. Its not at the top of the pedal and I do have to push fairly hard. Never tried it with the stock ones.

Good. Now just wait to see if you've got heat problems. If you don't (and you probly won't) then you're good 2 go. Leave it to good enough, or get one of the engineers around here to run to numbers for ya (I'm too tired.)

But here's an important point. Heat is a function of work. The BMW brakes aren't doing more work than stockers, therefore they aren't generating more heat.

I stand alone on this club in that I really like the KFP's for track work.
but I also have used portefields in multiple street cars with some track experience.

I'm not the autox guru... but I don't think you can go wrong with the portefields. probably the Street version if you putting that many road miles on.

I'm guessing that once you change pads you won't have to work very hard to lock up at will...

more importantly, you will stop faster and be more resistant to heat fade since a competition pad is designed to work best under a competition heat range...

however, you will dirty your wheels a lot more and need to learn different brake techniques including modulation...

oh... you may or may not start warping your rotors too.

ha

What are KPFs? Not for this car, but I'm building a 3.0 6 conversion that I will definately TT. Maybe I'll cycle more and build my my legs and leave my BMW calipers be.

The whole point of BMW calipers (or any other calipers with bigger pistons) is to reduce the amount of pedal effort for a given braking force. This doesn't mean you will automatically generate more heat. Heat is a function of the mass of the car, the speed you bleed off, and how much braking force you apply (at the caliper, not at the pedal). If you generate no more force at the caliper than you do with the stock calipers, then no more heat will be generated, and the pads and rotors will last just as long.

Of course, if this is what you do, the whole point of using the bigger calipers in the first place is rather lost.

The main downside to bigger front calipers only isn't so much the potential for extra heat and fade, but the fact that the brake balance has now been moved substantially forward, reducing the percentage of braking supplied by the rear tires. You have four tires, you might as well use all of them to contribute to braking. If you don't, you're reducing the amount of braking possible by overloading the front tires and underusing the rear tires.

So, using BMW calipers on the front is fine if you prefer the feel, but it's not a legitimate performance upgrade, since the overall performance of the car is actually reduced.

Karbon Fiber Products.

(I know carbon is spelled with a C)
they are the same pads that used to be called "cool carbon"

I don't know if the company was bought out or just decided to do a name change. They are carbon ceramic pads with a carbon heat shield built into the backing. when the name changed, so did the color.
what used to be an "orange" grade of compound became "gold"

I run gold front and rear on my wheel to wheel car.

I used to run Blue fronts and Orange rears on my old race car way back around 96'
I run gold fronts and Portefield R4 rear on my semi-street daily driver that I will be using for DE

My race shop believes they are superior for lightweight vehicles.
my own experience echo's this. I really like the Port's for above 2500lbs. They were far superior on the old 944Turbo I built. But the KFP's seem much better on the lighter cars like a teener.

brant

No. This is wrong. There is no more heat generated, and no more fade. With bigger pistons on the brake side, means for more travel from the pedal, because the size of the master cylinder will remain the same and will have to fill more area with fluid. Also, the front brakes do most of the work, the rears only hold the car straight during braking. If you're car tends to "float" during braking, then you need more brakes on the rear. It takes a HUGE difference to do that.

The advantages of the BMW calipers are better heat displacement from the Al alloy, and lighter unsprung weight (which isn't a braking upgrade at all.)

My car has BMW calipers with SC vented rotors in front with SC calipers and vented rotors in the rear. Brakes worked great during my last track day. Fronts were a little prone to lock up in some cases.

If I had a stock 4 I would stick with stock calipers and rotors.

I think they were discussing the older BMWs that used non-vented rotors. I believe they work with stock 914-4 rotors...that is the simplicity of the swap. But I don't think you gain anything since you can not disapate any more heat than with stock since you don't have vented rotors with that set up.
That is why I decided to go with M calipers and vented rotors with the magic billet hubs up front. Since my car is a track/AX car I don't want brake fade after a 30+ minute run session...

I'd like to see a before and after test run using a G-Tech to really put this to bed.

I don't see that the BMW calipers are that much of an improvement over stock. Maybe just MAYBE the BMW calipers will take longer before fade begins to effect performance. But I don't see this ever being a factor on the street. If you are overheating your brakes driving on the street you need to slow down or you live at the top of a very tall hill.

And as far as the BMW calipers requiring less pedal effort. How do you measure this? How do you know this is true? Also, locking up the tires and sliding is not a indication of "better" brakes. Your stopping distance is shorter when you don't lock them up.

IMHO the people that have done the BMW conversion say they can "feel" the differance because thier wallet feel the difference. The easiest/quickest/cheapest way to improve brake performance is to upgrade your pads, flush the system of old fluid and BLEED, BLEED, BLEED the system.

I run stock calipers and Cool Carbon pads.

One of the dumbest and most dangerous things to happen to me was failing to completely release the emergency parking brake on my girlfriend's Toyota before a drive on the interstate. After driving for many miles and apparently overheating the rear brakes and boiling the fluid I found to my amazement that the brake pedal went completely soft as I exited the highway on an off ramp. "Oh, shit! No brakes!" Thankfully it was one long off ramp. Pump, pump, pump. The damn thing finally stopped. Scared the crap out of me! Then I realized the brake handle was partially up. Duh! Talk about feeling stupid.

Most of the heat generated in the brakes goes to the rotors not the calipers.
So if you upgrade to BMW calipers, with no rotor upgrade there is no greater heat disipation.
The advantage of the BMW rotors is that the pad surface area is greater.
This has the potential of making more heat sooner, up to the point of lock up, however that helps in performance.

I know it's true because I know the basic physics involved. Bigger caliper pistons with the same sized master cylinder piston means more mechanical advantage from the larger hydraulic ratio. This means less effort at the pedal for the same force at the caliper AND longer pedal travel for the same travel at the caliper piston. At some point as you increase the caliper piston size or reduce master cylinder size (same thing), you require so much extra travel at the master cylinder that you can't deliver enough fluid to press the pads against the rotor, and improvement ceases rather abruptly.

At some point before that, the long travel and light effort starts to "feed bad", generally feeling mushy even when perfectly bled. The brakes feel touchy and hard to control. I know this, because I've felt it myself (not on a 914).

In the opposite direction, as you reduce the size of the brake caliper piston(s) relative to the master cylinder piston, the brakes feel firmer, and travel is shorter, but pedal effort rises. At some point, the brakes begin to feel "wooden" and seem to lack power. Beyond that point, even the strongest person won't be able to lock up the brakes no matter how hard they press the pedal. I know this, because I've felt it myself (again, not on a 914).

In the middle, there's a sweet spot, which is fairly broad. Some people prefer the softer pedal with more power, others prefer the shorter pedal and put up with pressing harder. The BMW calipers shift the feel to the "soft/long" end, where using a 19mm MC with otherwise stock brakes moves you to the "hard/short" end. The stock 17mm MC with stock brakes is somewhere in the middle. The difference with the BMW "upgrade" v. the 19mm "upgrade" is that the caliper swap shifts the brake balance as well as altering the feel. This is esp. bad if you're also swapping in a heavier engine, as that by itself shifts the static weight rearwards, and you're shifting the brake balance forwards.

No. As counterintuitive as it seems, pad area has NO effect on braking force (and thus no effect on heat generation). Greater pad area spreads the load over a greater area of pad, so the pad wears more slowly, and generally can absorb more heat before fading. So, bigger pads ARE a benefit. However, by themselves, they don't generate any more heat.

Again, heat generation is only affected by how much weight you're slowing, and how quickly you're trying to slow it.

I think Brad's big beef with the BMW calipers is not that they add more heat to the rotor.. but that they prevent heat from leaving the rotor, since the pads cover a larger % of the rotor. You have to admit that an uncovered rotor will transfer heat to the air faster than a covered rotor.

Let us not forget the availability of options for pads. With stock there is Pagid? and what? I have not found a decent pad for our cars that was not 60-80. For that money I can get Mintex or Hawk for my Jetta, and those pads are 2x larger. There is more demand for the bmw pads so thier price is lower. Also let us not forget that we can order rebuilt calipers for the bmw that do not cost us to refi our homes.

BMW Calipers are not AL (the one's we're discussing here). Although I am agreeing with Alien Life Form for a while here. Stock brakes in the proper working condition work just as good. Most conversion were done on tired stock systems and got fresh BMW systems... not a good comparison.

Stock brakes are every bit as good and the entire system (yes, p-valve and all) works perfectly for any narrow bodied car in any situation up to heavy road course work and even then some (Brant) would argue that you're not driving properly. The cool thing about stock brakes is... you already own a set and you can waste your money on other cool things you must have like huge sway bars and oversized t-bars (tongue firmly in cheek)

If you have a hard time locking up stock or BMW calipers you need new pads.

The best money spent is on this...

Everything else.

I switched out my recently rebuilt fronts for a set of rebuilt BMW calipers just to see if it helped in AX.(Brakes were getting soft after double runs)
Yes, less brake fade and more control.

For the street a waste of time IIHO

I have since gone to 911 vented rotors and bigger calipers since I hate brake fade on track days.

Goign back to the pad question. The Porterfield's in my experience are excellent track pads. They stand up to heat VERY VERY well. With minimal fade. On the other hand, I don't think they're a very good autox pad, especially with a 914. The Porterfields are very grabby, even when cold, which is good for the track where your wheels are rotating at very high rpms, and have very high momentum. At an autox however, the wheels are rotating at much lower rpms, and hence less momentum. With the grabbiness of the Porterfield's, it makes brake lock-up much more likely, and they are harder to modulate at autox speeds. I've found, especially after going to lighter wheel and tire combinations, that a soft, simple pad is best for autox. Yes, you can still lock 'em up, but the difference between first bite and lock up is a lot larger with softer pads, and allows for much better modulation.

Just my $0.02...

-Josh2

Ok, I just ordered "The best money spent on this" I'll bring it with me on Aug 12th Riverside Autocross and compare it to what everyone is doing.

Yes, Hank's book is a great wealth of information...

Hank is along time friend...Every student (90 of them) for our GGR/Zone7 AX school held this past weekend recieved a copy as part of their registration packet weeks in advance of the school so they could come slightly prepared.

Our students have been getting a copy of this book for over 15 years

Common [necessary] knowlege for braking. More here:
http://stoptech.com/tech_info/tech_white_papers.shtml

I just added BMW brakes and may have opened this can of worms. I can say this. I like the BMW calipers better but they are not the end all be all. I got them cheap and figured I would try them out. I don't think they will stop all that much better but five or ten feet is a lot when it is needed. I am looking for a set of almost worn our Porterfield R4S pads for the stock calipers. If I can find them I will run some scientific test (BMW VS. Stock). I do like the feel of the BMW calipers better and with the up graded pads they clearly work better. I think the pedal modulation is better. As for the heat, it is negligible under my type of use

I also plan I taking out the proportioning valve or adding less bias to the front. I am going to try and run some test of before and after results. This should show how much the proportioning valve makes a differerence and how much the back brakes help in stopping.

I think my friend put it best. "We play with these cars for fun, it is not an investment, expect to loose money and have fun doing it." I installed the BMW calipers mostly to learn, play around and to wind down from work.

So.. If I add 6 piston Carrera GT calipers to the front of my solid rotor'd 914 will it stop?

Brant,

I didnt know Karbon people where back

Run BMW calipers!!

I hate the pedal feel. It does not build confidence in the driver having what appears to be a mushy pedal at all times no matter how much you bleed them.

As far as heat goes: All the math and physics in the world couldnt tell me what I learned at the track one day. Same style 2.0 powered 914's running within 1 second of each other. One had stock brake calipers front and rear with Porterfields and the other car with BMW's and Porterfields.

The BMW car had MUCH higher rotor temps (150deg+) than the other 4cyl car. I know there are a lot of variables, but if you have driven a stock 2.0 injected 914 around a race course, you would know that brakes are used very lightly in most cases.

B

regarding Karbon brand,
ordered another set of front golds about 5 weeks back..
so they are still out there, just not easy to find.

and conway at carquipt has been a dealer in the past too.
I've bought from him previously.

brant

Ask any motorcyclest and they will confirm: Back brakes make a noticeable difference in stopping distances! Same goes for cars

I wouldn't recommend pulling the prop. valve on a street car as you don't want your back brakes to over-power your fronts. You want the fronts to do the lion's share of the braking.

I have always used cool carbon/KFP Magnum pads on my race car.
A lot of the performance brake companies don't even list a pad for the stock rear calipers.

B.S.
Motorcycle racers don't even use rear brakes except for "tail wipping" Which is the motorcycle equivelent of drifting, which has nothing to do with stopping. One of the guy's I know (he and his wife race crotch rockets,) dosen't even have rear brakes on his race-bike.

The rest is right-on. No more arguements.

I use the BMW caliper setup on my 2.0 litre 4 full race car along with early 911 rear calipers with Hawk Blue pads all around. I also use a brake bias control and a 19mm master with Wilwood 550 fluid. My experience is that the brake pedal travel is greater and feels much softer then stockl It really takes some getting use to, but does have the desired result.

GB

Once again, Chris, you're talking one tiny sample and generalizing it way out of proportion.

Yes, many bike riders only use the front brakes. I did most of the time when I was doing that. The weight transfer from a bike with a fairly high CG and a fairly short wheelbase (which describes most sporting machinery) does indeed often render the rear brakes nearly useless except in special cases, like getting the rear end out (which can actually be very useful for stopping and turning at the same time, I've seen more than a few top pros "drifting" around tight hairpins very successfully as a passing manuever). Some racers also prefer using the rear brake to some degree, anyway, even if the rear tire is very lightly loaded. Mick Doohan, an Australian that won several world titles, insisted on using the rear brake extensively. When a serious leg injury made using his braking foot very difficult, Honda fitted a thumb operated brake on the clutch-side handlebar for him so he could still use the rear brake.

Not ALL bikes have a very high CG and a short wheelbase. Harleys and Harley-like bikes, for example, frequently have a very low CG and a long-ish wheelbase, and often have a static rear weight bias, esp. with a rider, as the seat generally places the rider quite far back on the bike. This dramatically increases the usefulness of the rear brakes, and using both brakes at the same time will substantially reduce stopping distances.

Bikes are a great way to experiment with brake bias and how it's affected by static and dynamic weight distribution.

I put on the BMW calipers when I first bought my car as a quick and relatively cheap way to get the brakes working. Now I hate them. The feel is mushy and the fronts are doing all the work. That's why Brad measured higher temps on the rotors with BMW calipers at the track. The car with the stock set up was using more of the rear brakes and distributing the heat load more evenly. I am definitely going back to the stock front calipers as soon as I can get them rebuilt. All else being equal, I believe the stock setup will out brake a set with the BMW calipers.

Where is there a good source for the KFP pads and what model do you recommend for AX?