Differences Between Brembo 380mm/380mm BBK and 365mm/345mm BBK

[swamp2]

Originally Posted by robc

Sort of, in a closed system yes, kinetic energy is all that matters mass * velocity = X no matter whether it takes 5 seconds to go from v1 to v2 or 10 seconds.

To be clear Ek = 1/2 m x v^2, even dropping the 1/2 is OK in some engineering calculations or scaling arguments but m x v is momentum not energy.

[swamp2]

Lucid: I can appreciate your desire to design and fabricate your own kit. It should be relatively simple. Especially given the prices TMS wants for their E46 M3 kits. I can only imagine what they will want for their E92 kit, $1k+ for sure. Hmmm have I used the expression "M Tax" before... In all fairness I guess it is 4 CF parts in the kit with fairly complex surfaces which involves some decent design work and tooling expense...

[lucid]

Originally Posted by swamp2

Lucid: I can appreciate your desire to design and fabricate your own kit. It should be relatively simple. Especially given the prices TMS wants for their E46 M3 kits. I can only imagine what they will want for their E92 kit, $1k+ for sure. Hmmm have I used the expression "M Tax" before... In all fairness I guess it is 4 CF parts in the kit with fairly complex surfaces which involves some decent design work and tooling expense...

The plan is to do more than just brake cooling...

[robc]

Originally Posted by swamp2

To be clear Ek = 1/2 m x v^2, even dropping the 1/2 is OK in some engineering calculations or scaling arguments but m x v is momentum not energy.

Momentum and energy are basically interchangeable and not significant for this discussion -- until we can complete both sides of this "equation" using the exact rate of heat dissipation at v, it's academic to be specific with energy v. momentum, since even if we were to, computing J or P would get us no further since we do not know how much air flows at what rate(s) over what part(s) of the rotors to even begin to determine how many J could be dissipated in the form of heat between corners.

But, you are correct, it was lazy of me to oversimplify the computation of energy and then to speak specifically of it, my bad, been 16 years since my last physics course, I'll check my formulas next time.

[SenorFunkyPants]

Originally Posted by lucid

The surface of the rotor would indeed reach a higher temperature if you brake harder and shorter during braking (conductivity of the rotor and the time scale is a factor there). But again, convection during braking is negligable, so any heat loss consideration to the environment is not an issue during that time interval.

"convection during braking is negligable" I guess that it may be negligable relative to the amount of energy being put into the "brakes" under heavy braking but the amount of heat being dissipated will still be significant and relative to the temp of the rotor and air flow over it.
I recall the old days of F1 when you could see the iron brakes flare up bright red under heavy braking and then quickly lose the colour. Which also reminded me of the cooling ducts they used which IIRC were little more than "horns" attached to the backing plates collecting from the air flow over the car. Is there enough space to do something similar to the M3 but collect from the air flow under the car?

[lucid]

Originally Posted by SenorFunkyPants

"convection during braking is negligable" I guess that it may be negligable relative to the amount of energy being put into the "brakes" under heavy braking but the amount of heat being dissipated will still be significant and relative to the temp of the rotor and air flow over it.

Yes, that is what I meant. When the timeframe is longer (the majority of the a lap is driven with brakes off--straights and corner exits--and potentially at high speed), convective cooling adds up and becomes critical in maintaining the overall energy balance of the system.

Originally Posted by SenorFunkyPants

I recall the old days of F1 when you could see the iron brakes flare up bright red under heavy braking and then quickly lose the colour. Which also reminded me of the cooling ducts they used which IIRC were little more than "horns" attached to the backing plates collecting from the air flow over the car. Is there enough space to do something similar to the M3 but collect from the air flow under the car?

I was speaking with a BMW shop owner the other day, and he recommended the exact same approach you mention here. He said some p-cars actually have plastic "scoops" that are clamped onto the control arm, which simply channel air in the direction of the rotor and showed me an example. I don't know which car the part came out of exactly, but I assume it was an older p-car. There is no reason why such a simple approach would not yield improvement, but we'd still need to cut hole in the existing shield behind the rotor as there is not much of a gap between the rim and the shield for air to flow through.

[consolidated]

Originally Posted by lucid

He said some p-cars actually have plastic "scoops" that are clamped onto the control arm, which simply channel air in the direction of the rotor and showed me an example. I don't know which car the part came out of exactly, but I assume it was an older p-car. There is no reason why such a simple approach would not yield improvement, but we'd still need to cut hole in the existing shield behind the rotor as there is not much of a gap between the rim and the shield for air to flow through.

All 997 and 987s have a brake cooling deflector on the lower control arm. There are different sizes and designs between models, I replaced my Cayman S deflectors with 997 GT3 parts, a typical mod, just a bit larger and only $22 if I recall. They snap onto the arm w/o fasteners.

[jml]

Originally Posted by consolidated

All 997 and 987s have a brake cooling deflector on the lower control arm. There are different sizes and designs between models, I replaced my Cayman S deflectors with 997 GT3 parts, a typical mod, just a bit larger and only $22 if I recall. They snap onto the arm w/o fasteners.

That's a pretty ingenious idea. I wonder how much airflow is under the E90 in that area.

[lucid]

Originally Posted by consolidated

All 997 and 987s have a brake cooling deflector on the lower control arm. There are different sizes and designs between models, I replaced my Cayman S deflectors with 997 GT3 parts, a typical mod, just a bit larger and only $22 if I recall. They snap onto the arm w/o fasteners.

Thanks for the pics! There clearly is a break in the shield. I'll have to stick my head down there and see where the control arm is on our cars with relation to the rotor. This is not the ultimate fix, but it surely will help!

[doba_s]

Originally Posted by lucid

Thanks for the pics! There clearly is a break in the shield. I'll have to stick my head down there and see where the control arm is on our cars with relation to the rotor. This is not the ultimate fix, but it surely will help!

take some pictures of that area ... my car is in the service right now and I can't take a look at it myself ...

[lucid]

Originally Posted by doba_s

take some pictures of that area ... my car is in the service right now and I can't take a look at it myself ...

I'll try to do that today.

[robc]

Originally Posted by lucid

I was speaking with a BMW shop owner the other day, and he recommended the exact same approach you mention here. He said some p-cars actually have plastic "scoops" that are clamped onto the control arm, which simply channel air in the direction of the rotor and showed me an example. I don't know which car the part came out of exactly, but I assume it was an older p-car. There is no reason why such a simple approach would not yield improvement, but we'd still need to cut hole in the existing shield behind the rotor as there is not much of a gap between the rim and the shield for air to flow through.

Already did this, have hoses attached to the control arms, have for about a year now, will find the pics and post.

[JAJ]

Originally Posted by lucid

Thanks for the pics! There clearly is a break in the shield. I'll have to stick my head down there and see where the control arm is on our cars with relation to the rotor. This is not the ultimate fix, but it surely will help!

I made some of these out of thin aluminum sheet for my E39 M5 - they bolted onto the backing plate at the bottom and the steering knuckle at the top and collected and channeled air into the holes in the center of the backing plate (which I left intact). If I can find the picture I took of them I'll post it later.

With the factory air ducts opened on the E39 and my spinnakers in place, brake cooling was excellent.

I've been thinking of ways to do this same thing on the E92. The problem with designing something is figuring out how to keep your creation from getting tangled up in suspension members or hitting the lining of the wheelwell in a sharp turn. And of course, there's the whole question of "where's the necessary cold air going to come from when there are no brake ducts to open?"

I was on Tischer's site yesterday pricing front backing plates and bumper parts. I was thinking about doing some cutting and patching new metal that would make the the backing plates into scoops to catch air at the bottom and pull it into the hub and rotor.

I've studied the front bumper and wheel-wells from underneath a bunch of times but never really figured out how to get cold air channeled from the front bumper to a place where the scoops could pick it up. BMW's airflow design for under the car creates a low pressure area just behind the bumper, so there may not be a good source of cold fast-moving air without reconstructing part of the front bumper. I've been suspicious all along that BMW designed the airflow for the brakes to go from outside-to-inside, pulled along by the low pressure zone under the engine.

Anyway, if my suspicion is correct and if all there is is a jumble of turbulent air flowing away from the rotating tire toward the center of the car, then putting a scoop on the backing plate won't cool the brakes more effectively. More than once I've concluded that I really need a wind tunnel. In fact, I might just get a big fan and make one just so I can figure this out.

[swamp2]

Originally Posted by robc

Momentum and energy are basically interchangeable and not significant for this discussion -- until we can complete both sides of this "equation" using the exact rate of heat dissipation at v, it's academic to be specific with energy v. momentum, since even if we were to, computing J or P would get us no further since we do not know how much air flows at what rate(s) over what part(s) of the rotors to even begin to determine how many J could be dissipated in the form of heat between corners.

But, you are correct, it was lazy of me to oversimplify the computation of energy and then to speak specifically of it, my bad, been 16 years since my last physics course, I'll check my formulas next time.

Absolutely not interchangeable. Regardless of if the calculation involves any cooling or not. Any calculation stemming from the basic principal of conservation of energy requires the right equation and the right units. To a first approximation during parts of braking sequences energy is conserved, wheraas momentum is absolutely not. The difference in magnitude is clear as well as energy builds much faster with v than momentum does. I've done plenty of brake design work and plenty of calculations on this topic. They simply are not interchangeable, not with respect basic physics, units nor when doing rough or finer calculations.

[swamp2]

Originally Posted by consolidated

All 997 and 987s have a brake cooling deflector on the lower control arm. ...

Good post and good pics. Thanks a lot for that. This is obviously one important ingredient to the legendary performance of P car brakes (well really light cars and really big brake helps as well....). This looks like a great idea for a simple and easy to install aftermarket part for the M3. Does Porsche run these front and rear or just front? Do they run them on all of their models?

[SenorFunkyPants]

Originally Posted by JAJ

I've been suspicious all along that BMW designed the airflow for the brakes to go from outside-to-inside, pulled along by the low pressure zone under the engine.
Anyway, if my suspicion is correct and if all there is is a jumble of turbulent air flowing away from the rotating tire toward the center of the car, then putting a scoop on the backing plate won't cool the brakes more effectively.

Given the amount of effort BMW have gone to in order to produce a fast smooth flow of air below the car would they really want to introduce turbulent air from the spinning front wheels into the flow under the car?

[robc]

Originally Posted by swamp2

Absolutely not interchangeable. Regardless of if the calculation involves any cooling or not. Any calculation stemming from the basic principal of conservation of energy requires the right equation and the right units. To a first approximation during parts of braking sequences energy is conserved, wheraas momentum is absolutely not. The difference in magnitude is clear as well as energy builds much faster with v than momentum does. I've done plenty of brake design work and plenty of calculations on this topic. They simply are not interchangeable, not with respect basic physics, units nor when doing rough or finer calculations.

Come on, I said discussion. The rudeness I experience when I post every five years makes me not post for another five years. Sheesh. Sorry I don't live up to your standards. I'll post my pics and go back into hiding and not share anything I learn here ever again.

[robc]

Here are the pics of what I did, I cover the "intake" with duct tape when not on the track (and try to angle them further down to catch more air when I am on the track).

[lucid]

Originally Posted by robc

Here are the pics of what I did, I cover the "intake" with duct tape when not on the track (and try to angle them further down to catch more air when I am on the track).

Thanks for the pics. OK, that might partially explain why you are not running into major temperature issues with your rotors. I can't see the other end of the duct. How do they attach to the shield exactly? Did you cut a hole throught the shield?

[lucid]

Originally Posted by JAJ

I've studied the front bumper and wheel-wells from underneath a bunch of times but never really figured out how to get cold air channeled from the front bumper to a place where the scoops could pick it up. BMW's airflow design for under the car creates a low pressure area just behind the bumper, so there may not be a good source of cold fast-moving air without reconstructing part of the front bumper. I've been suspicious all along that BMW designed the airflow for the brakes to go from outside-to-inside, pulled along by the low pressure zone under the engine.

Anyway, if my suspicion is correct and if all there is is a jumble of turbulent air flowing away from the rotating tire toward the center of the car, then putting a scoop on the backing plate won't cool the brakes more effectively. More than once I've concluded that I really need a wind tunnel. In fact, I might just get a big fan and make one just so I can figure this out.

These are all good points to consider, but without data, it's hard to tell. Regardless, I find it a bit hard to believe that BMW has tuned things to the extent that air flows from underneath the car and out through the wheels (and cools the rotors in the process) if that's what you mean. The stock shield constitutes too much of an obstruction for this to be the case and the spokes of the wheels do not seem to be designed to further enhance such flow IMO.

This is great discussion guys. Thanks for your contributions!

[nkweisberg]

I had the backing shields behind my front rotors removed when I put in my Dinan springs and camber plates. The backing shields behind my rear rotors were cut off. So far one track day with these and I think it made a difference? Turner is supposed to be working on a kit. I would imaging that the M3's that race in the Koni challenge have figured something out. Also my track rims (CCW C10's) have MUCH more room around the calipers than the OEM 19's. I wonder if this helps with cooling, cannot hurt I suppose.

Would Stoptech's with the same pads and fluid take the heat better than the OEM setup with upgraded pads/fluid??? Kicking around the idea of Stoptech's. Cost is making me take pause.

I'm going to the PCA event at Sebring this weekend and will see how the brakes hold up. I hit 145 on the back strait at Palm Beach Intl Raceway (Moroso). The speeds at Sebring should be higher.

[lucid]

Originally Posted by nkweisberg

Would Stoptech's with the same pads and fluid take the heat better than the OEM setup with upgraded pads/fluid??? Kicking around the idea of Stoptech's. Cost is making me take pause.

In general, this depends on the mass of the BBK rotor vs the mass of the stock rotor. Having more thermal capacity means the rotor will experience less temperature gain for the same amount of heat generation while braking. However, depending on how demanding you are of the brakes, without additional cooling, increasing the thermal capacity somewhat might not solve the problem (it might only delay it) as the overall energy balance of the system can still be positive into the rotor, but we need more information to be able to say anything conclusive. That said, I am also looking into the Stoptech and Brembo kits. My rotors are shot, and I don't want to sink $800 into the stock rotors.