A bit bored this AM, so I'm rambling a little...

The 19mm MC used with otherwise stock 914/4 brakes: this results in a reduction in braking force for a given pedal force (forcing you to push harder to stop), and the actual amount is 16%. Some people like the "firm" feeling this provides, but it doesn't mean "better braking".

The 19mm MC used with BMW 320i calipers OR Porsche M calipers (same size). This results in a 12% decrease in pedal effort for a given braking force. So, you will feel an improvement, but it's not a very big one. The downsides to this swap is the bigger calipers are heavier (unsprung mass, too), and of course you're doing a lot of work for a pretty small gain. You're also doing nothing to help brake fade. You're likely making it more likely, since you can now load a bit more heat into the brakes more easily. Happily, this also won't have a huge effect on front/rear brake bias, however, since the overall effect is so small.

A 17mm MC used with M calipers would produce quite a big change in pedal force v. braking force: 33%. However, this MAY cause a problem in that the 17mm MC is small enough that you couldn't move enough fluid with it before you run out of pedal travel to fully press the pads against the rotors. You'd certainly have to push it a long way to get the brakes to come on at all, and the brakes would likely feel touchy and mushy, but powerful. Rather like overboosted power brakes...

btw, "17mm" and "19mm" (and "42mm" or "48mm" for caliper piston diameters) aren't strictly correct. Even in metric countries, brakes are actually specified in 1/16ths of an inch, so 17mm is really 11/16, or 17.45mm, and 19mm is really 3/4 (12/16) 19.05mm. 42mm is really 26/16", or 41.275mm, and 48mm is really 47.625mm. Germans just list the sizes in the nearest metric size, whereas the Japanese perversely use both systems: 10mm for some parts, and 0.50" for others, for example.

better braking = rebuilt shea calipers, good bleeding with good fluid, good lines...

after that, 911 brake setup IMHO

I had BMW brakes, and they are no better than stock that works...


I like the 19mm M/C.. .feels stiffer... but I think with stock brakes, a 17mm is all that's needed...

It appears your rambling is just a tad off, when in the second paragraph you mention you don't do anything for brake fade, but with M calipers and vented rotors the heat dissapation is increased quite a bit. In the 2004 Tecate race I suffered brake fade but after installing the 4 bolt alloy hubs, M calipers and vented rotors in 2005 I had no brake fade. I think I drove pretty much the same, maybe a little harder even.

QUOTE (john rogers @ Mar 30 2006, 12:20 PM)

It appears your rambling is just a tad off, when in the second paragraph you mention you don't do anything for brake fade, but with M calipers and vented rotors the heat dissapation is increased quite a bit. In the 2004 Tecate race I suffered brake fade but after installing the 4 bolt alloy hubs, M calipers and vented rotors in 2005 I had no brake fade. I think I drove pretty much the same, maybe a little harder even.

I didn't mentioned vented rotors, John. Just calipers. Plenty of people fit BMW calipers to the stock 914/4 rotors, and early M calipers, too. Fitting vented rotors requires a lot more work.

First you need to decide whether you really need to up grade your brakes or simply rebuild the stock units. Porsche engineers designed the system that is one the the car. In hteory, with stock tires, wheels, and sprung weight, stock brakes in good tune should work excellent.

It has always been my opinion, that up-rated brakes have less to do with the amount of HP the car has, and much more with the changes in weight, wheels, tire diameter, contact patch, and balance.


stopping an 85 hp from 60 mph and stopping 500 hp from 60 mph, is no different if both cars weight the same and have the same tires/wheel and contact patch.

QUOTE (rick 918-S @ Mar 30 2006, 01:49 PM)

It has always been my opinion, that up-rated brakes have less to do with the amount of HP the car has, and much more with the changes in weight, wheels, tire diameter, contact patch, and balance. stopping an 85 hp from 60 mph and stopping 500 hp from 60 mph, is no different if both cars weight the same and have the same tires/wheel and contact patch.

The primary reason, however, for upgrading brakes with large increases in power is that on a tight road/track, you'll be hitting 60mph in places where before you were only hitting 40mph, so you'll need to brake from the higher speed down to the same speed (assuming the weight really is the same, same cornering speeds) more often. In this case, you really need to upgrade the "fade resistance", so you need bigger and/or vented rotors more frequently than you need bigger calipers.

Of course, one rarely sees big increases in power in a 914 w/o big increases in weight, too. A V8 powered 914 is 20-30% heavier, at a minimum, than a 1.7 powered 914. The V8 is also going to shift the weight back, so you need more rear brake bias to fully take advantage of this. So, bigger calipers just on the front will not help this.

A turbo Subaru swap would probably weigh about the same as a stock 914, so you only have to handle the additional power, and could certainly get away with no brake upgrades at all, unless you intend to push the car hard on a tight course.

QUOTE (lapuwali @ Mar 30 2006, 02:09 PM)

QUOTE (rick 918-S @ Mar 30 2006, 01:49 PM) It has always been my opinion, that up-rated brakes have less to do with the amount of HP the car has, and much more with the changes in weight, wheels, tire diameter, contact patch, and balance. stopping an 85 hp from 60 mph and stopping 500 hp from 60 mph, is no different if both cars weight the same and have the same tires/wheel and contact patch. The primary reason, however, for upgrading brakes with large increases in power is that on a tight road/track, you'll be hitting 60mph in places where before you were only hitting 40mph, so you'll need to brake from the higher speed down to the same speed (assuming the weight really is the same, same cornering speeds) more often. In this case, you really need to upgrade the "fade resistance", so you need bigger and/or vented rotors more frequently than you need bigger calipers. Of course, one rarely sees big increases in power in a 914 w/o big increases in weight, too. A V8 powered 914 is 20-30% heavier, at a minimum, than a 1.7 powered 914. The V8 is also going to shift the weight back, so you need more rear brake bias to fully take advantage of this. So, bigger calipers just on the front will not help this. A turbo Subaru swap would probably weigh about the same as a stock 914, so you only have to handle the additional power, and could certainly get away with no brake upgrades at all, unless you intend to push the car hard on a tight course.

Close... Here's my expanded thought on the subject. It still doesn't matter if your traveling 60 mph with an 85 hp car or if your traveling 60 mph with 500 hp. All things being the same the car will brake the same. When things change is when you add HP, stock tires and standard width wheels are no longer transmitting the added torque. When you move up in tires and wheels, the increase in weight, diameter, and contact patch, this decreases the brakes ability to stop the added mass. Think about adding a 4' pipe to your breaker bar.

I haven't done the math, but my gut feeling is the increased rotational inertia of heavier wheels/tires won't have a big effect on the brakes. There will be SOME, but I think the effect would be relatively small. I'll have to try to calculate the effect sometime.

QUOTE (lapuwali @ Mar 30 2006, 08:17 PM)

I haven't done the math, but my gut feeling is the increased rotational inertia of heavier wheels/tires won't have a big effect on the brakes. There will be SOME, but I think the effect would be relatively small. I'll have to try to calculate the effect sometime.

WOW I wish I knew how to find the info but in a Grassroots motorsports magazine not to long ago they upgraded the brakes(on a neon) to some really beefy road race brakes and also upgraded to larger tires. I could have swore they lost 15 feet or so slowing from 100mph. But they did eliminate brake fade.

You would figure with the huge wheels and tires and huge brakes it would stop faster but it didn't. Think rotational inertia might have played a part in this.

That is why folks putting Dubs on their SUVs should be upgrading their brakes....huge increase in rotational forces.

On my particular car I upgraded to Ms in front and 914-4 fronts in the rear.
I did this to get increased fade resistance for the track.
with my tire combo which will have a smaller overall diameter and increased braking efficiency I am looking at much greater overall performance.

I run rebuilt stock calipers with Porterfield r-4's race pads all around.
Stock MC, prop valve, SS soft lines.

These are fantastic. I've yet to find the limits on the track.

For the street I can't imagine any better.
Anyone who rides along is stunned


KT

If all your doing is a single brake test from 60mph to 0 then yes it does not matter
if your car has 500hp or 85hp.

If your upgrading your brakes for track events (not autox), there is a big difference
between a car that makes 500hp or 85hp. You carry so much more speed every
where and your on your brakes sooner because you got there faster. Less time
for your brakes to cool also.

Yup. I experienced this with my car at the wcc.

Before then I never got the brakes hot... But once I got them hot, they stuck like glue... and I KNOW I was on the brakes a lot more than most of the cars... when I was pushing the car.

Andrew

Cool thread.

Thought provoking stuff before my pragmatic view:

* Larger wheels and tires generally = larger contact patch - Talk amongst yourselves.
* Excellent new tire and pad compounds - Talk amongst yourselves.

My pragmatic view:

Stock 914 brakes were over-engineered for their day, just like any Porsche brake system. This mark is known for the best brakes in the business.

Today's tire compounds are leaps and bounds over what was available in the 70's... so are today's pad compounds.

If you have a 914 with stock fenders you're 'probably' good to go with stock brakes. If you are racing said 914 in a 'serious' road course environment you'll want to look into brake 'system' solutions. There's evidence of this within this thread (John Rogers).

If you're autocrossing you'll generally be good with stock brakes but it would do you well to get good pads. There's evidence of this within this thread (Trekkor).

BMW brakes are not an 'upgrade'. If you think they are, you had really shitty brakes on your car before you put them on. The exact same 914 with BMW brakes and stock brakes will stop in the same distance. Your tires (contact patch) will be the limiting factor. He/She who locks up his/her wheels faster stops last... sliding is not stopping. 914 brakes can lock the wheels with the right pads (even with most wrong pads).

If you've successfully increased your contact patch through the use of flared fenders and wider tires you could probably benefit from a larger brake system. If you haven't, you're probably just trying to be cool

Flared 914's, with the exception of all but the largest wheels and tires can be successfully stopped on a regular/race basis with a set of A or S-Calipers. Anything larger is probably bragging rights. These cars raced for 24 hours back on June 13th and 14th of 1970 with 908 calipers (basically an S-Caliper with fat-ass pads). They were around 220hp, lightened a bit and had 7-8x15" wheels and race tires of the day. They won their class in that little race called "LeMans"!

What do you plan to do with yours?

Talk amongst yourselves...

This thread is hitting close to home right now. I have a dilemma. I was planning on flaring my car and using some custom widened pedrinis I have, with Eric Sheas calipers. In fact Eric has already rebuilt my front calipers and the rears are packed in a box ready to go. I also have the FG flares (I planned to rivet, not bondo) and GT rockers.

Fast forward to now. I picked up this new 73 2.0 for a song loaded with an SC front end and 16x6 Fuchs. Plus a ton of other bonus parts.

Here is my dilemma:
A: go forward as planned flared with four lug widened Pedrinis (which are totally bitchin BTW).

B: go forward NARROW with five lug fuchs, SC front end and dial the rear to match.

C: go forwad WIDE with five lug fuchs, SC front end and dial the rear to match.

I am leaning towards B for now, and C can always come later. I can't see forefeiting the SCbrakes and 5 lugs.

More rambling:

When "improving" brakes, you can really only do threethings: reduce the chance of fade, reduce pedal effort, change brake bias front/rear.

Reducing pedal effort can be done two ways: change the hydraulic ratio of master cylinder to calipers, or add a power servo. Adding a servo to a 914 is possible, but pretty difficult. Altering the ratios is certainly doable, and can make a difference. There's a sweet spot on ratios, which ranges from about 18:1 at the low end and 24:1 at the high end. Lower than 18:1 (master cylinder too big), and the pedal feels "wooden", there's very little pedal stroke, and you have to push hard enough that you end up losing the ability to modulate the pressure. Higher than 24:1 (master cylinder too small), and the brakes feel mushy and touchy. Pedal stroke is quite long. You also run the risk of running out of pedal stroke before the calipers are fully pressurised, since the small MC can't push as much fluid. These numbers are strictly empirical, and it really is a "feel" issue before it starts to become a safety issue. On a 914/4 with stock calipers, the front brakes are 22.3:1 with a 17mm MC, and 18.8:1 with a 19mm MC, so they're both in the sweet spot, but at opposite ends of it. 20:1 would likely be the most pleasing to most people, but there's no off the shelf combination of Porsche parts that will get you there. And yes, the front and rear brakes are considered separate systems, since the 914 uses a dual MC. The combination of the rear brakes will also affect feel. The ratio at the rear should be less than the ratio at the front, or you need an adjustable proportioning valve to reduce the pressure at the rear calipers, so they don't lock first.

Reducing fade is usually the most worthwhile goal in improving brakes, and certainly what you need to do if you're going to track the car. This cannot be accomplished by just swapping calipers. You must either change the pads (the material CAN make a difference), or enlarge the rotors, either with larger diameter rotors, or vented rotors (or both). The downside of rotor swaps is that they add unsprung mass AND rotational mass, the former making the suspension work harder, the latter making the brakes work harder. If you're a zillionare, you could go with ceramic or carbon composite rotors, of course. Using lighter aftermarket calipers can help offset the additional mass of the bigger rotors, though that won't help the rotational problem (which I need to characterize).

Improving brake bias is, I think, the overlooked upgrade for the 914. I wish I had more data, but I get the feeling that the 914/4, as stock, is actually underbraked at the back. This is a "safe" engineering decision, since preventing premature rear lockup is important in a street car to be driven by non-experts. However, I get the feeling some useful braking is left on the table by an overly aggressive front/rear proportioning. With the usual adjustable proportioning valves on the market, you can only get a useful change in brake bias by also fitting much larger rear calipers, since all these valves can do is reduce the braking to the rear. If you don't have enough braking at the back to begin with, you end up with a valve that's merely open (i.e., a Tee).

I'm currently have the parts to go with a '89 SC front end w/ "A" calipers, 19mm m/c, ss lines, stock rear calipers, w/no proportioning valve and Porterfield pads.

Hope it works...

here are a couple of my thoughts on the subject:

a. the BMW "upgrade" is more trouble than is it worth.

b. unless you live at the top of Mt. Hood, I don't thnk a street car only driven on the street will EVER have a problem with brake fade.

c. I have stock calipers on my car. I realize I'm stopping less car than everyone else, but even when I did track events they were fine.

d. Never heard of anyone having fade problems at an a/x.

I know most of what I just said has been said above but I didn't want to be leaft out.

Paul,

When I saw you name up on the list, that's exactly what I thought as the thread was loading... stock brakes for that car.

Helps prove the point and with all your points.

QUOTE (URY914 @ Mar 31 2006, 10:43 AM)

b. unless you live at the top of Mt. Hood, I don't thnk a street car only driven on the street will EVER have a problem with brake fade. c. I have stock calipers on my car. I realize I'm stopping less car than everyone else, but even when I did track events they were fine.

Paul, I know you live in Florida, where you only see mountains in pictures, but some of us do live in areas where the best roads are full of steep downhills with lots of hairpin turns. I've never faded the brakes on a 914 on these roads, but I have cooked brakes on other cars on them.

You're stopping a LOT less than most of us. You 914 weighs less than my Mini, which is factory-equipped with drum brakes all round that are only 7" in diameter. You're probably overbraked now. Time to turn down those rotors to shave off a bit more weight...

More braking on the rear, that is what I thought when I used BMW calipers on the front and rear with a tee. They worked amazingly well until I put in the six and started driving the car harder since the high torque from the stroker four was not there any longer. After the six I added the M calipers and vented front rotors and cut out a slight amount of rear brake bias.

One thing no one has mentioned is something like titanium heat sinks between the pad and piston to shield the heat some from the fluid. I have seen some old time SCCA racers use this and there were lots of racing Porsches with Titanium pistons if I remember correctly?

QUOTE (Eric_Shea @ Mar 31 2006, 10:50 AM)

Paul, When I saw you name up on the list, that's exactly what I thought as the thread was loading... stock brakes for that car. Helps prove the point and with all your points.

It feels good when I get it right enough that someone agrees with me.
Lord know people don't always agree with me.

QUOTE (lapuwali @ Mar 31 2006, 10:51 AM)

QUOTE (URY914 @ Mar 31 2006, 10:43 AM) b. unless you live at the top of Mt. Hood, I don't thnk a street car only driven on the street will EVER have a problem with brake fade. c. I have stock calipers on my car. I realize I'm stopping less car than everyone else, but even when I did track events they were fine. Paul, I know you live in Florida, where you only see mountains in pictures, but some of us do live in areas where the best roads are full of steep downhills with lots of hairpin turns. I've never faded the brakes on a 914 on these roads, but I have cooked brakes on other cars on them. You're stopping a LOT less than most of us. You 914 weighs less than my Mini, which is factory-equipped with drum brakes all round that are only 7" in diameter. You're probably overbraked now. Time to turn down those rotors to shave off a bit more weight...

"I've never faded the brakes on a 914 on these roads..." But we're talking about 914's here, so nuff said.

BTW I am thinking of drilling some holes in the rear rotors. That cast iron is HEAVY!!!

So, I bought rebuilt BMW calipers about a year ago, along with 19mm MC. I later learned that these are probably not necessary. Since I was not impressed with the stock brakes on my car before I disassembled the whole thing, then they were probably in bad shape and needed replacing rather than upgrading. However, since I've got new ones I will go ahead and use the BMW stuff w/ the 19mm MC. BUT, I understand the stock rotor does not like BMW brakes given they are solid. I saw cryogenically treated rotors that were slotted and drilled for a pretty good price. They are solid and not vented, but being a superior material and "vented" via slots and holes, they should help brake fade with the bigger MC and caliper, right? I guess the real question is whether they can perform like regular vented M rotors or are they just a mediocre compromise? Thoughts?

Worthy upgrades? Itmes that fight a brakes biggest problems - heat!

1) More air to cool the brakes
2) "stickier" brake pads and good brake fluid

I learned those when tracking my SC. The overall brake performance was fine, the issue was fade. Remove the fade, and the brakes are good. Sure, I may have been putting more heat into the rotors due to the change in grip of the pads, but the additional airflow helped dissipate the heat at the same time.

Mediocre compromise. The slots and holes don't do much to give you extra surface area to radiate the heat away, nor do they do much to promote airflow across the surface area that is there. Real vented rotors have around double the surface area of solid rotors, and they actually create air flow through the vents. Both of these are good for cooling the brakes.

--DD

Speaking of airflow... does anyone know where the brake ducts pictured on this site

http://members.rennlist.com/sjanes/brakes.htm

can be sourced from? I've tried using the email from the site but it bounced.

And would they be effective?

The Hoover vacuum company... =)

Kidding!

But seriously, looks home brewed to me.

I was once told by a famous race car engineer that you can go only as fast as you can stop.

As my head cocked he then said "exactly" !

That person was Mac Tilton

So what are some nice brake upgrades available today....I have been away for a while and am just getting back into the 914 again.

I would expect the best upgrade to be 911 brakes.

I have a 71 911T front suspension on my 914 with S/S lines, 19mm master cylinder with a rear brake adjustable proportioning valve. Discs were new when installed, calipers overhauled, new Ferrodo pads and wheel bearings installed. It was awesome!!

I have just acquired some nice alloy 4 piston Boxter brakes and adaptors for the 914 rear trailing arm and 3.5" 911 front struts.

They mate up with vented (and drilled) 911 rotors. This is an excellent conversion as it is way more brake than my 3.2 914 will ever need...even on the track.

The larger pad area (with greater potential clamping force) spreads out the load on a larger rotor surface which dissapates heat more quickly...the alloy caliper saves some unsprung weight to offset the increase in rotor weight....end result should be a brake system that requires less pedal pressure for equal clamping force...it will also have a greater potential range (which increases feel for modulation) and will dissapate heat more quickly eliminating any need for ducts, hoses or fans...oh, and as this system works at the lower end of it's potential, it should last longer as well.

The trick now is to choose a good pad that works in the right heat ranges without chewing up the rotors....and then set the bias.

Car not ready for a while...but I'll report when she is.

AJ USA has them

I was late for a meeting when I posted this. Here's some more info.

The brake coolers work very well. They even work better when you run the tubing to the front air dam. See vents in pic

Click to view attachment



I actually have a fiberglas version of the coolers from OGRacing that has 3" tubing v.s. the 2.5" tubing on the AJ kit. OGRacing lists replacement tubing that mentions their "cool brake kit", but I couldn't find the Cool Brake kit itself? You probably need to contact them if you are interested. When I ordered mine, I got the whole story of 3" tubing flow v.s. 2.5" and also that their kit was a copy of the Al Holbert racing coolers.. I'm very happy with the OGRacing kit. But to be honest, the 2.5 tubing is easier to route. I have some clearance "challenges" with the 3" tubing but it is workable.

Thanks for the reply, Dave.

Of course! I never thought about the vents on vented rotors actually creating air flow. But naturally, cause they are like a really narrow squire cage fan!

So, mediocre compromise on the cryo rotors... Hmm... I'll need to think this one through. I don't believe I'm ready for the full 5 lug conversion to get 911 brakes, but since I'm preparing a turbo WRX engine for my car right now, I'm gonna need to stop this thing. I'm afraid the stock brakes aren't going to cut it. But, based upon Lapuwali's assertion, the BMW brakes might not give me that much gain anyway, even if they were slotted. Oh well, I will research some more. There is a wealth of info here so I'll go find it.

Holy thread resurrection, Batman!

Ha! Yeah. I think in academia they call Lapuwli's contributions to the body of 914 knowledge a "primary source". (At least based upon the limited time I've had to peruse topics, seems like that to me.)

Not a bad place to start.

Drilled and slotted rotors are designed to vent hot gases that build up inder the pads in extreme braking conditions.

The AJ kit is good for cooling rotors.

I miss James.

Eric,

You are right on when you say "Miss James". Great thread with great comments.

Steve Hurt

word