Any air flow experts out there? Brake cooling question.

[moneymanager]

The brake cooling hoses (only 2.5") on my early 911 are always a problem...limiting the car's turning radius in tight quarters, getting caught on something, etc. Seeking a solution without routing the hoses thru the trunk, I wonder if the following would work. Bear with me a minute.
The cross-sectional area of a 2.5" hose is (a = pi r squared) about 5 sq inches. Could I run the hose to some point under the car, transition to a square "pipe" 5" x 1", thus getting the right area, then transition back to 2.5" hose? My thought is this would preserve the airflow and open up (2/5" - 1") 1.5" of space in a tight spot. Anyone know if my theory is sound? Or would the transition cause so many strange effects the air wouldn't flow properly? Any thoughts welcome.

[Bill Verburg]

You are on the right track in wanting to use bigger hose. It's a real problem. Through the trunk is obviously best, next best is routing so that the A arm is inside the tube.

Use smooth bore tube, minimize bends, have as large and as forward centrally located a pickup as possible, pay attention to transitions.

[barney911rs]

I've seen things like that done on GT3 RSR's, except it was all done with carbon fiber. I'm looking to do something along those lines myself. I'm tired of ripping the scoops off the bottom of the control arm. But with a race car, I'll cut holes in the trunk if need be to run the cooling.

Take some pics of what you end up doing, I'm sure others would like to see your solution.

[moneymanager]

Thanks guys. If I figure something out, I'll be sure to run pics.

[randywebb]

Bill is giving you the 4 commandments there. I'd add to choose a high pressure area for the inlet, but you likely will 'have to' anyway.

One rephrasing of a commandment can be made:

Air "doesn't like to turn corners" so make any curves as gentle as possible.

[moneymanager]

I've been thinking about trying something like this for a long time but have always been detered by the apparent absense of successful attempts by others. WHen someone has a good idea for solving a problem like this, usually people copy it and you see it around. Funny that in all the forty years 911's have been around hardly anyone has tried this. Maybe its just that the amateurs like me just make do while the pros cut holes thru the trunk and cut right to the chase!

[Bill Verburg]

Originally posted by randy webb
I'd add to choose a high pressure area for the inlet,

"forward centrally located a pickup as possible" that is where the high pressure area is

The air moves faster as it slips to the sides creating lower pressure areas, especially near the corners

[911pcars]

Or try forced air. A couple of marine bilge exhaust fans reduces the length of inlet hose and path configuration and minimizes the ID requirements (slightly).





Sherwood

[911pcars]

Brake duct through the trunk. Direct and out of harms way.



Sherwood

[moneymanager]

Hi Sherwood,
Really? THis is a great idea. I was yesterday looking at the Jasbro product line...they make bilge pumps among other things...for another item. Never occurred to me to put two and two together. Still using your gate shift device...works great.
Jim Taylor

[Jack Olsen]

It'd be great if someone were able to measure the actual cfm of air flowing through typical nose openings and ducts and compare it to blowers like Sherwood shows. There's no such thing as free energy with an electric fan, of course, but it seems like there might be a worthwhile tradeoff if you could evacuate air from a no-benefit high pressure area (like ahead of and above the front wheels), and use a blower to keep the brakes showered in a constant (i.e. not speed-dependent) stream of cooling air.

[Bill Verburg]

Prosystems has all the stuff you need

GeorgeM did a nice piece on his setup a while ago, You might try search

[moneymanager]

Just looking at a 3" Attwood bilge pump...100 cfm for $20. Doesn't it seem like over a cubic foot of air per second would be enough?

[911pcars]

Forgot to mention this in-trunk ducting also has water mist cooling to reduce the air temp. So does the race car in my earlier photo. This is only practical (or needed) in a track car.



Sherwood

[randywebb]

Originally posted by Jack Olsen
It'd be great if someone were able to measure the actual cfm of air flowing through typical nose openings and ducts ...

This can be done w/o too much trouble. Anemometers such as are used in HVAC work are not too expensive. I actually have a very nice fan type with great bearings but I haven't had time to calibrate it, measure the stall speed and stick it in my little brake duct that I don't need anyway...

Heated bead or hotwire types are common these days. They give very local readings, but you can just measure at teh center and near the walls to get an idea of the profile.

You aren't tired of experimenting are you Jack???

[randywebb]

Some wind-pollinated plants use the sharpness of the bend in tubes that lead to the female sex organ to control the size pollen that gets in to mate. The bends slow the air and make foreign species pollen drop out if it is too big & heavy. At a different place along the tube, the process is reversed and the too-small pollen is sent rushing into oblivion, and the right sized "good stuff" drops down onto the plants' - um - "egg." et voila.

I don't have those reprints anymore, but did a quick search and found this interesting article. You will _enjoy_ adapting this research to your car....

Science 30 July 1982:
Vol. 217. no. 4558, pp. 442 - 444
DOI: 10.1126/science.217.4558.442

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Articles

Pollination and Airflow Patterns Around Conifer Ovulate Cones
KARL J. NIKLAS 1 and KYAW THA PAW U 2

1 Section of Plant Biology, Cornell University, Ithaca, New York 18453
2 Department of Agronomy, Purdue University, West Lafayette, Indiana 47907

Wind-tunnel studies indicate that the geometry of Pinus ovulate cones may enhance the probability of pollen entrapment by aerodynamically predetermining airflow patterns around scale-bract complexes. Pollination experiments reveal that pollen from a particular species has the highest probability of reaching the ovules of its own species. The phenomenon of species-specific pollination appears to be related to the specific morphometry of scale-bract complexes and the terminal settling velocity of pollen of the same species. These data are interpreted as evidence for a reciprocity between the aerodynamic characteristics of airborne pollen and ovulate cones of some conifer species.

[Jack Olsen]

Originally posted by randywebb
You aren't tired of experimenting are you Jack???

Nope. But then, I've never had brake fade.

I have 964-style diverters, 930 brakes, and a light enough car so that heat has never been a problem.

[Bill Verburg]

Originally posted by Jack Olsen
Nope. But then, I've never had brake fade.

I have 964-style diverters, 930 brakes, and a light enough car so that heat has never been a problem.

The anti big brake crowd just don't understand the meaning of that statement!

Not every one needs them, but if you do, da*n the weight, full speed ahead!

[moneymanager]

Just thinking out loud here. Over the course of a mile, if you had a 12" x 12" opening in the front of your car, 5280 cubic feet of air would enter it. The much smaller 2.5" air duct we were talking about above would admit about 3.5% of that or 183 cubic feet of air. At one mile per minute, or 60 mph, that 183 cubic feet of air would flow thru the duct every minute...
Now a typical marine bilge blower puts out maybe 150 cubic feet per minute...so I'm thinking it might help keep the brakes cool at low speeds, say under 50, but that at higher speeds it would just be in the way...that is the ram air available at speeds over 50 should be way more than the small fan could ever deliver. So what looked like a really great idea may be less interesting than it seemed!

[Mahler9th]

My car is very light and doesn't really need ducting, but I have it anyway since I never want to have a problem. Like many other 911 cars, I get the air out front in the bumper. I use the SmartRacing Products manifolds to help with issues around the control arms. I have posted in other places my approach to sealing off the backside of the rotor. As I read the original post, the issue isn't so much effectiveness, but rather convenience-- my guess is that the control arms are a big source of that frustration. The SRP manifolds really help with that. Of course you can make your own similar set up.

If you really want to or need to get fancy with brake ducting cooling, I'd suggest that you use the Puhn book as a technical resource.