I might be in danger of over simplifying a complex issue, but here goes.....

I am considering ways to increase hp in my teener, and want to know how far up the hp curve will the stock brake setup carry me (or stop me actually)?

My issue is that I love my polished 4 bolt fuchs, thus have little interest in a 5 lug conversion. So...it seems that to keep the 4 bolt setup, I am pretty much limited to a BMW brake upgrade up front. Correct?

So for a street car that might see an AX one day, what would be a reasonable hp limit for stock brakes? For BMW brakes?

Oh yea, I already have a 19mm m/c and SS lines.

thx

well.... if the billet hubs ever came out.... you could run 911 veneted rotors and M calipers and stay 4 lug......


paging mr mueller....

or you can make adapters and run wilwoods, brembos etc... the choice is yours...dont be late (nirvana)

The size of the brakes will also depend on how big the tires are since 205 sized tires are happy with stock or BMW calipers. It also depends on what type for racing, if any you do. If it is street only, stock is good, auto-x or time trials then maybe BMW's on the front or if you do road racing where the course is lots of short straights such as I do in Mexico, then bigger calipers and vented rotors are necessary. This would figure a top HP of 200 or so, anything over that would need additional work on the car.

when you exceed 109.75854 horsepower.

That number is the result of some serious math. Many hours of calculation went into that.

QUOTE (jr91472 @ Apr 5 2005, 12:35 PM)

When to go big brakes

when your current brakes can't lock up the tires anymore ...
or, when you get brake-fade due to overheating ...

Andy

QUOTE (Aaron Cox @ Apr 5 2005, 01:38 PM)

well.... if the billet hubs ever came out.... you could run 911 veneted rotors and M calipers and stay 4 lug......

1st set going out on Wednesday...they'd go out today, but with it being my B-day today, I'm leaving work in just a few minutes

they are going to a 914club member who races his car and will put these puppies to the test

and if you are reading this, you are getting 2 brand new billet hubs, I'll take the beat up prototype unit back to abuse more

Well Happy Birthday!!!!!

I agree with Mr. Rodgers, tires are the limiting factor when you're pushing the car. I haven't a clue where *that* line is as *which* tire also enters into the equation and what you are doing with the car.

Having said that, more brake than tire is a gud idea.

QUOTE (J P Stein @ Apr 5 2005, 01:23 PM)

I agree with Mr. Rodgers, tires are the limiting factor when you're pushing the car. I haven't a clue where *that* line is as *which* tire also enters into the equation and what you are doing with the car. Having said that, more brake than tire is a gud idea.

Up to a point. I've driven cars with LOTS more brake than tire, and it's scary. Instant lockup with very little modulation or control.

There is no real correlation for "this much power means that much brake". The issue is how much speed, and how far that speed needs to be reduced, which often has very little to do with engine power, and a lot more to do with driver ability and style.

Much like Andy said, you need more brakes when you're running out of them. Stock 914 brakes in perfect working order will work just fine up to pretty silly speeds.

all depends on tires....

when i had tiny stock 165 tires... stock brakes would lock them up like crazy....

now i have sticky azenis's and my 911 M calipers *can* hardly lock them up....

more tire equates to more brakes...

QUOTE (Brett W @ Apr 5 2005, 01:02 PM)

when you exceed 109.75854 horsepower. That number is the result of some serious math. Many hours of calculation went into that.

cool stuff.....thanks everyone

I agree with the others. Your more likely to need to increase the clamping force on the rotor if you change the size diameter of your tires and or increase the un-sprung wieght with heavy after market wheels and or the contact patch of the tires. It's alot less about the size of your motor. 60 mph is still 60 mph. Just because you get there faster doesn't mean your going any faster. In this case size in HP really doesn't matter.

The board went down. I found this to be an interesting topic. Thought I'd give it a bump. It's a common question.

As a side note, the brakes on our 1987 930 at one time were just about the best $$$$ could buy. I have done a few really hard stops from 150 + MPH and it still takes a long time to stop! What was amazing was they could do it time after time and not fade so the heat disappation with those huge vented rotors is a huge factor. I have noticed that in most of the vintage races I do I can brake just a little bit later than many of the 911 guys and we have about the same tire footprint. Our brake caliper size is about equal so I attribute it to slightly better weight distribution. I did note however that last year in Tecate MX that a 944 spec car was on my ass during braking most all the time so we were both on the limit. I'll get to see in a couple of weeks as the first race of the Baja series is in Tecate MX. I think the vented rotors will most definately eliminate any chance of fade.

QUOTE (lapuwali @ Apr 5 2005, 01:37 PM)

Having said that, more brake than tire is a gud idea. [/QUOTE] Up to a point. I've driven cars with LOTS more brake than tire, and it's scary. Instant lockup with very little modulation or control.

I agree with this....to a point.

The only cars I've driven with this problem have power (over boosted) brakes and it was some time back....like 40 years
when the technology was fairly new. I think it's nearly impossible to have non-boosted brakes that are too sensitive....but I've been wrong before.

As to the power to brake question:
Granted, 60 mph is 60 mph, but......with more power, one can get to 60 mph ...say on a race course...whereas a less powerful car can only get to 40 mph....which car needs more brakes? Often, more power = more weight....like a SB chebbie conversion or even a 6. Tires are still THE limiting factor, but not the only one.

Maybe some examples would be more helpful in actually answering this question in a more practical sense.

I have way overkill brakes and a 1.7 so I really can't comment.

How many of the V8 guys are running stock brakes? How many brake related failures (fading, glazed pads, whatever) have they experienced? If any, what did they switch to to solve it? What about the sixes? What about big 4's? Autocross? Street? Track?

QUOTE

Horesepower has nothing to do with brakes.

More HP creates more heat. More heat has to go somewhere. Stock brakes were designed to operate on a car with 80hp and tires that are rock hard and very narrow. If HP doesn't affect braking requirements why did Porsche feel it necessary to put a vented rotor on the stock 6 or why do the 944 turbos have more brake than the base model 944.

When I was talking to a Porsche guru this weekend he was telling me about the braking test that the factory uses to certify its brakes. They take each model and accelerate to 80% of top speed and then lock the car down to a halt. Then accelerate the car back to the 80% of top speed and do it again. This is done 40 times in a row. if the brakes fail then they go back to the drawing board. This test benefits the cars with less HP, because they take more time to get back up to speed, thus allowing more cool down time.

I do agree that traction, weight, and speed all affect braking. The 914 comes with fabulous brakes for a producttion car. Look at the brakes available on some other production cars. Most cars come marginally braked from the factory.

So when are the billet hubs coming? I need 2 sets!

Cheers,

Louis

I have 'A' calipers on the fronts, stock rear's vented all the way around, and racing pads.

I had problems with locking up my tires at the autox... Tires are street tires... So if I had Hoosers on it would probably be different....

Andrew

QUOTE (Andyrew @ Apr 6 2005, 02:24 PM)

I have 'A' calipers on the fronts, stock rear's vented all the way around, and racing pads. I had problems with locking up my tires at the autox... Tires are street tires... So if I had Hoosers on it would probably be different.... Andrew

Do you lock the fronts, the rears, or both?

Really dont know.

I think I locked the fronts, but driving the other day, I tested locking up the brakes and the rear started to come around a tinsy bit when I locked them up.

The stock 914-4 brakes are just fine for a 914 street car.

After converting my 914 to a 140hp 2.4L sixer, I drove around on the stock 914-4 brakes for 5 years(50-60K miles). No problem stopping, even from up around 120mph.

I finally tired of hearing I didn't have enough brakes on the car and I do like the looks of the 5 paddle Fuchs, so I converted the 914 to vented 911 brakes, etc. Ever since, I've had to treat the brake peddle with care. I found out the hard way the 911 brakes can flat-spot a set of 205/60/15s real quick!

Hi
You guys should hang with me and my buds on a Friday nite, this is the kinda thing we "discuss"
Thanx to the guy that bumped, I would of missed this.
I agree 100%, I am not overly interested with the 5 bolt conversion, take the 911 stuff, probably for 90% of the people that have it, its overkill. I have your set up now with a mild beefed 2.0l, LOVE the way it brakes (195/60/15) now I am upping the anti, 220 hp, BMW stuff, with the most widest tire that could possibly fit on a 914 (modified hubs and mags).
I think you got things figured out rite...one things for sure, if you outgrow a BMW conversion with big tires, you are in "supercar" catagory, lots of guys here has/needs the big guns, but not for me.
Good luck with it
Regards
Joe

QUOTE (morgan_harwell @ Apr 6 2005, 02:40 PM)

After converting my 914 to a 140hp 2.4L sixer, I drove around on the stock 914-4 brakes for 5 years(50-60K miles). No problem stopping, even from up around 120mph.

Interesting Morgan, thanks for joining in....

QUOTE (jr91472 @ Apr 6 2005, 04:10 PM)

QUOTE (morgan_harwell @ Apr 6 2005, 02:40 PM) After converting my 914 to a 140hp 2.4L sixer, I drove around on the stock 914-4 brakes for 5 years(50-60K miles). No problem stopping, even from up around 120mph. Interesting Morgan, thanks for joining in....

the stock 914 calipers have 42mm bore pistons, the 911 calipers have a 48mm bore (same as the popular BMW caliper ugrade)...so for Morgan, his pedal should have to travel further, but it'll create more pressure at the pads....Morgan, what did you do for the rear calipers?? did you keep the prop. valve??

thanks

I have 2 pot Volvos on the front with 19mm M/C they work very good and were not expensive to convert. I would like to put vented discs on but need the hubs for that.

Bernie

110/140 - Porsche used M-Calipers and Larger Rears (914-6/911E)
160/240 - Porsche used S-Calipers and Larger Rears (911S/930)
250/??? - Sky and the wallet are your limiting factors.

I try to make things simple cuz I'm stoopid sometimes

QUOTE (Brett W @ Apr 6 2005, 03:06 PM)

When I was talking to a Porsche guru this weekend he was telling me about the braking test that the factory uses to certify its brakes. They take each model and accelerate to 80% of top speed and then lock the car down to a halt. Then accelerate the car back to the 80% of top speed and do it again. This is done 40 times in a row. if the brakes fail then they go back to the drawing board. This test benefits the cars with less HP, because they take more time to get back up to speed, thus allowing more cool down time. I do agree that traction, weight, and speed all affect braking. The 914 comes with fabulous brakes for a producttion car. Look at the brakes available on some other production cars. Most cars come marginally braked from the factory.

I think this would be more of a case of marketing versus actual engineering. As Porsche increases the performance of a particular car in one area they increase the performance in others so that the car maintains an overall balance. I've heard that the reason that the 914 didn't get the whole 911 suspension/brake set-up was because a 914 would out-brake the 911 due to it's lighter weight and this wouldn't sit too well with 911 owners who felt the 914 was an inferior car.