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Northern Motorhead
 
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OK Boys,

Here's a few preliminary shots of my "El Cheapo" Ajusa wannabe air deflector plates
with a %^$@#* lip ... Yep,the lip is a major PIA but in the end it makes the plate more solid.

I had no choice but to make my own due to the 8 1/4 inch center of my 13 inch rotors but with a lot of time and some scrap metal everything is possible !

I'll post more pictures of the final installation.

Cheers !
Phil





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1983 944 SP2 race car
Old 05-10-2012, 12:05 PM
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Quote:
Originally Posted by wildcat077 View Post
Chris,

Which part would that be,guessing it's from the later 997 Cup cars ?
I now have 13 inch rotors in the front so the regular 911 stuff doesn't work for me anymore ...

Cheers !
Phil
Pretty sure the Cup rotors are that big. I know there is still most of a part number on mine. I'll check it and report back. If the Cup clamshell and GT2 Scoop is good enough for Porsche, pretty sure it'll work for you. Rotors ont he Cup are some 13" or more...
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Old 05-10-2012, 12:07 PM
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These are the ones that were on my car if it helps.



Old 05-10-2012, 02:54 PM
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I would be interested to hear/see an engineering explanation as to why whatever the current Cup cars (which are all out race cars from the factory) do for cooling air to their brakes. And why that works for them. And if it would work for those of us running basically stock brakes on close to stock race cars. I haven't heard of Cup cars having a "running out of brakes" issue, at least not in short races (in long ones they often have to change pads, but that is a different matter than managing the heat).

Looking at the Cup car parts catalog, I see an air deflector (much same, if not exactly same, as on street 997s) but nothing more - no special backing plate, no hoses, etc. If there is enough air flow for the deflector to grab, no reason why it should not work. But braking is a package - and in some of our cars (SCs, Boxsters, for instance), I am quite certain that the system, from the thermal capacities of rotor and caliper to the amount of cooling air flowing here and there, air directing scoops aren't going to do the job

I know I favor center-out-through-the-vanes cooling because that's what Holbert designed and sold. Hardly scientific, but makes a lot of sense (after all, those vanes are not there only to reduce rotating mass, are they?). And for something really trick, try Wilwood (or anyone else's, if there are any) curved vane rotors, which really act as an air pump and have to be installed on the proper side so they do that instead of impeding the air flow.

Puhn wrote two books. His first, on handling from 1981, says a lot about brakes from a mechanical advantage standpoint, but doesn't say much about the best way to distribute cooling air to them. In 1985 he wrote a "Brake Handbook." Naturally this goes into everything in much more detail.

In it he is unequivocal about the superiority of directing air into the center of vaned rotors, sealing the entrance area as well as possible.

On open wheel cars he shows scoop-like ducts leading directly to this area, sans the intermediate hoses we all use.

Clamshell or clamshell-like approaches would be needed on solid rotors (if cooling isn't nearly equal on both sides, the rotor will warp), but he does not even hint at any superiority for this for vented rotors.

Anyone wants to experiment with this, be my guest. But on a car whose brakes are thermally challenged, I'd use the tried and true center directed air approach and would never consider a clamshell.
Old 05-10-2012, 03:01 PM
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I prefer an approach where we connect with what's been done and leverage it toward improvement.

Let me be more clear:

1. Brake systems on Porsches used for track work is an area where we do not have a lot of clear and obvious cookie cutter solutions. There are a lot of variables with brake systems and a lot of different cars and configurations, and a lot of different tracks. I have been corresponding about the cars on the 'net since 1994 and this particular area is one where I feel that there are so many variables, folks are best served getting local input from knowledgeable resources as a starting point. It can save time and money.

My selfish motivation is to encourage folks that the most expensive and elaborate solution isn't always required or optimal. This applies to rotors, pads, calipers, fluids and other aspects of system design.

Here is an example:

One of the most expensive Spec 911 cars we have is owned by a knowledgeable friend/Porsche lover/excellent driver. His son is a well-known pro driver and the shop develops and maintains his car is world famous.

He has well over $100k invested. And he is extremely knowledgeable technically. The brake system is custom and might represent a $5-10k investment. I think It is all custom parts and Alcon pieces, engineered by folks at the top of the food chain. Their design inputs include considerations having to do with the types of customers they have. I am sure it has various merits. But that level of spend isn't the norm in the class, nor is it required to have an effective and competitive system that meets Spec 911 rules. Ask Eagledriver here on the forum what he thinks is a good Spec 911 brake system or Toby. Not $10k.

If we did not keep folks aware of opportunities to apply a range of effective solutions, we would only have millionaire Spec 911 combatants. I feel we need participants with a wide range of resources to have a successful program. If we don't have enough racers, we have to have a different program, and none of us wants that.

I extend this feeling to Porsche ownership in general.

Sure, a hinged box flapper is a known, age-old solution for exploding plastic boxes in 911s. Brake systems are more variable. Similar deal for suspension systems for large groups of older Porsche cars.

Since the internet became a popular place to share this type of info in the 90's, I have seen a continual watering down of the info that has been learned by many in the past, and used to be shared in person-to-person communication. I think it is really sad, because I think we can all do better.

2. SmartRacing never made a brake cooling system. They sourced from AJ USA or AJ USA's provider.

3. I could find out for sure if I tracked it down, but I am pretty certain the AJ kit was designed for a specific combination of parts common to certain cars. I suspect that the lip is a design element to fill the gap between a reasonably thick metal backing plate affixed directly to a strut, and the location of the rotor's back side opening. In the case of my hubs and rotors, this gap is about 3/16 inch. If one wants an optimal seal, this gap ought to be dealt with. So we can make the backing plate a cone shape. Or we can shim out the flat backing plate so that it is even with the rotor backside opening. Or we can have a lip. The AJ USA parts sold by them and SRP have a lip. My home made parts also have a lip. And so on.

You can kind of get an idea about the gap in this picture.... the lip in my custom plates fills the stack-up gap to the backside of the rotor:




My car weighs 1900 pounds and runs on Goodyear slicks. The output is between 350 and 380 crank bhp. My needs are very different from a Cup car or RSR.

Recently I had the opportunity to spend an entire day visiting the HQ of the "de facto" Porsche factory RSR racing team. Since they have raced in GrandAm in addition to IMSA, they have run various configurations of cups and R, RS and RSR cars through the years. They don't necessarily run what Porsche ships them. When I was there it was a month before Sebring, and they had possession of likely two of the few (maybe only?) 2012 RSR cars. They were completely apart. Brand new cars from Porsche AG representing the factory effort. And they were being "done to."

I also got to see some of the various different brake system components they have put together over the years for the factory cars they have raced. Different design inputs have driven different solutions at different times. Even for different tracks.

By the way, I am not aware that any of them have included clam shells like some (all?) 917s and 935s ran. I am aware of some pretty intricate composite pieces used for brake ducting, including some pieces that mount to calipers. I held them in my hands. It is all intricate, carefully designed and expensive. One of the RSR duct pieces I saw was.... what $1000 or more? Just one side? Used?

Some of the stuff I saw is likely not available for just anyone to buy from PMNA.

By the way, they sell used parts at the "factory" team HQ...

Do you wanna know about brake systems in water-cooled factory cars? Ask Tommy Sadler, Craig Watkins and others dealing with this stuff. There are others as well. But pay them a consulting fee...

Some (most) of those solutions have nothing to do with some guy's 2800 pound 250 bhp 911 alphabet class club racer.


Come on man.
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Last edited by Mahler9th; 05-10-2012 at 06:38 PM..
Old 05-10-2012, 06:32 PM
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By the way, as I am sure that folks here know, some Porsche street car vented rotors have curved vanes and need to be installed on the proper side to work effectively. These also work like an air pump.
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Old 05-10-2012, 06:47 PM
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Quote:
Originally Posted by Mahler9th View Post
By the way, as I am sure that folks here know, some Porsche street car vented rotors have curved vanes and need to be installed on the proper side to work effectively. These also work like an air pump.
My 996TT rotors have curved vanes and are uni directional ...

Cheers !
Phil
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89 Coupe,Black,Cobra Sebring,6 pt roll cage,SW chip
Fabspeed headers, K&N,996TT brakes,Fikses,,Sanders 23/31 TB's ,turbo TR's, ER bushings,Wevo mounts,ER camber plates,Tarett sway bars,RSR strut bar mounts,95 3.6 engine and the list goes on ...
1983 944 SP2 race car
Old 05-11-2012, 03:50 AM
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A couple of years ago, when Denver's 3R Racing was running Porsches in Speed World Challenge, I was in their shop before the new season started. They had two brand new Cup cars in there, stripped. They said that various of the factory components, race or not, weren't up to the task, so they were making their own or reinforcing the factory stuff.

But that venue's rules differed from, say, the European Cup/Supercup rules, where you had to race the factory Cup car as it came from the factory.

I've never quite figured out what Grand Am's rules for Porsches are, but I know that a car racing as a Pontiac at the Daytona 24 hours three years ago had no significant Pontiac parts in it other than maybe the engine block. Basically a NASCAR silhouette approach.

SP911 is a pretty nice class and a cost conscious one, so I'd be surprised if one had to spend a bundle to get their car's brakes to where they never had a soft pedal during a race, no matter what the track. Not expensive to duct air effectively, and for $40 or so you can get a fluid good to 683 degrees F these days. Spending a bundle sounds like a guy doing things because he likes to design things more than because he needs to.
Old 05-11-2012, 08:13 PM
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Old 05-11-2012, 08:13 PM
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