Has anyone put brake air deflector on rear?

[midnight911]

I really like how 993 brake air deflector came out for my 84 carrera. With back plate off, the temp is significantly down and pad longevity has improved dramatically...at the track. measured temp with infra red gauge and now the front rotor/caliper temp right after a session is cooler than the rear. The rear also has no back plate.

I'm thinking if i could fab/ put something similar to the rear. just looking at the rear, the banana arm kinda gets in the way of where i'd want to put some deflector or a baffle. If i'm successful, i know i'd also be saving pad life for the rear. has anyone got any air baffling example for the rear?

[Bill Verburg]

Originally Posted by midnight911

I really like how 993 brake air deflector came out for my 84 carrera. With back plate off, the temp is significantly down and pad longevity has improved dramatically...at the track. measured temp with infra red gauge and now the front rotor/caliper temp right after a session is cooler than the rear. The rear also has no back plate.

I'm thinking if i could fab/ put something similar to the rear. just looking at the rear, the banana arm kinda gets in the way of where i'd want to put some deflector or a baffle. If i'm successful, i know i'd also be saving pad life for the rear. has anyone got any air baffling example for the rear?

here's what the 997GT3s use on their rear brakes






generally the rears don't run hot enough to warrant additional cooling

[midnight911]

Bill, thanks much. You know what it inspired me of something... I'm on my way to the home depot...

[Grady Clay]

Another little ‘trick’ is to use the heater tubes in the chassis.

If you still maintain your behind-dash fresh air system, you can simply temporarily re-configure the controls
and blow fresh air from the cowl to the rear brakes (assuming you are using headers).

With heat exchangers in place, you must make a “U-duct” to direct the heat exchanger waste air (very hot).
These ducts MUST have a restrictor in place so too much air isn’t allowed to ‘waste’ through the heat exchanger.
Make the tube extend down and back.

Even with the heat exchangers and ‘flapper valves’ in place, it is useful to use some
red (high-temp) heater hose to duct the output of the ‘flapper valve’ down and back.

Someone makes a part for the front brakes that seal to the rotor’s center vanes. All you
need is blow the cool air in that direction, including the caliper and pipe.


Why do BBS brake wheel-fans need to be sooo expensive.
They really work.
‘Before BBS’, racers used modified Corvair engine fans.

Best,
Grady

[midnight911]

Grady,
heat tube is exacatly what I had in mind, zip tied on to the banana-arm, mated to a rain gutter collector part...i have to worry about the ground clearance. Not figured that part yet.

The car is a 84 chassis with 3.6 and is a street car with all the heat exchangers, heaters in tact. Your solution seems very elegant but that's for a race car!!! :-)

[Grady Clay]

Actually the easy part you can do.

Take some of the red, wire-wound, silicon tube and hose-clamp it to the ‘flapper valve’ outlet. You can cut the hose for the control wire bracket.

I route hose ahead of the axle and then angle rearward. I made two little holes in the flange of the heat exchanger and bolted on a small support bracket. I used safety wire everywhere as it is too hot for zip-ties and more big hose clamps are too heavy.

Make sure it can’t come near the battery B+ terminal on the right side or the throttle linkage on the left. You need real wire restraints for these.

Mine touch things like the parking brake cables, heat control cables, trailing arms (slightly) and even the axle shaft (not boot) occasionally under extreme use.

This effort takes all that very hot waste heater air (and it is VERY HOT) and blows it down and back under the engine.

Not only does this keep the rear brakes cooler but it also reduces the temperature of the transmission and starter. We were doing this in the ‘60s. I think some 993s vent the waste air down and back.


When doing this, consider how it might fail. Most dangerous, I think, is to get wrapped around an axle and interfere with the throttle or short to the B+. (Make sure your B+ has a good boot zip-tied in place.)


I think there is still room for your down-facing NACA-Duct under the torsion bar tube and hose toward the brakes. Be sure nothing can vibrate against a brake pipe or hose. Keep in mind that as the suspension goes ‘up’ on ‘bump’, there is almost no clearance to the underside of the chassis. The tube will probably need to end before the inboard side of the chassis. That should be enough.

Inspect regularly. Adjust as necessary. I consider all this ductwork as disposable and install everything new periodically or when you have the engine/trans out.

Best,
Grady

[midnight911]

Grady, so what you are saying is that I should get the hot air out of the heat exchanger more efficiently, not just relying on the vents on the flapper box but via the flapper box outlet while the flapper vents closed? (the same effect as having the heater on all the time?)
And this removal of hot air from the heat exchange effectively cools the brake system, tranny, and starter a lot better?

[Grady Clay]

Originally Posted by midnight911

Grady, so what you are saying is that I should get the
hot air out of the heat exchanger more efficiently, not just relying on the vents on the
flapper box but via the flapper box outlet while the flapper vents closed? (the same
effect as having the heater on all the time?)
And this removal of hot air from the heat exchange effectively cools the brake system,
tranny, and starter a lot better?

Think of there being a “transmission compartment in the car.

The ‘compartment’ is sealed on the top by the back seats, on the front by the
torsion bar tube & bulkhead, on the sides by the frame rails & fenders and
on the rear by the engine tin. It is open on the bottom to the extent of
road clearance.

When the heaters are off (summer track use), all of the hot heater air is pumped
(by the engine fan) into the top of the ‘transmission compartment’. Remember,
heat rises and the heater air coming out of the heat exchanger ’flapper valve’
is a LOT HOTTER than winter heater use.

The only air flow into the ‘transmission compartment’ is from the opening between
the pan and the road. The air is exiting under the engine. I’m sure there is some
‘come & go’ at the sides.

Conclusion:

Put the outlet of the ‘flapper valve’ at the bottom rear of the ‘transmission compartment’.
This is closest to where the air is exiting the ‘transmission compartment’.

You do this by extending the ‘flapper valve’ outlet with some hose.


I have not done an air flow study of the ‘transmission compartment’.
This is simply an application of ‘common sense’.

Best,
Grady

[Wil Ferch]

Grady:

Where were you when I posted this in 2003?--->

http://forums.pelicanparts.com/porsche-911-technical-forum/96425-heater-valve-discharge.html

[MotoSook]

Originally Posted by Grady Clay

Another little ‘trick’ is to use the heater tubes in the chassis.
.
.
.
.

Why do BBS brake wheel-fans need to be sooo expensive.
They really work.
‘Before BBS’, racers used modified Corvair engine fans.

Best,
Grady

Great trick with the heater circuit!

BTW: the BBS wheel fans, I assume are the plastic fans that fit on the Fuchs wheel bore, right? How expensive are they?

[midnight911]

will see if this works...

[911 tweaks]

might this be blowing asbestos/brake material up into the heater tubes which at some point provide heating air to the cockpit...??
I believe asbestos has been outlawed/banned from brake shoes now, but, something to consider...how about what ever is used now for the brake pad materials...??

Not trying to pooh pooh anything here...this thought just entered my mind...what do you all think about this...?? (maybe I am missing something here which I would not be suprised of...)

Great idea though from Grady...

Bob

[midnight911]

this time, i didn't incorporate Grady's advice. So, the tube is not connected to the flapper box. It's just facing forward so that the air flows into the tube and to the rear half of the rotor. If the car is rolling forward, i do not think the fume from the brake goes forward thru the tube.

i still think keeping the hot air from stuck in the pocket is a very good idea. to do that, i could just replace the tube I have out the heat exchanger with a u-shaped tube and vent the hot air rearward...

[jpnovak]

Here is a post from long ago. Yeah, I remembered it was still there. There are some really good ideas in this thread. [begin movie-like wavey lines of time]

http://forums.pelicanparts.com/porsche-911-technical-forum/8623-project-little-reds.html


Trivia time: Does anyone still recognize the screen name? Do you know what his new screen name is? Hint: He has a suspension business.

[911 tweaks]

would the company be elephant...?? :-)

[Walt Fricke]

Wil

There have been some other discussions about the design of the Porsche hot air ducting and valve.

Since I do not believe that cooling the heat exchangers is important, I used to block off the fan exit for the heat exchange system in the engine compartment on the SC (with '74 headers and exchangers) for summer track use. There is a rubber plumbing cap with hose clamp which is perfect for this.

Engine did not run hot as a result, though I did not do careful before and afters, it was before I had an IR heat gun, etc.

But I've never had an issue with rear brakes overheating, so haven't done much other than remove the dust shields.

Craig Watkins had NACA ducts in his lower (and detachable) rocker panels on his GT4 track car 10 or so years ago.

Walt

[Flieger]

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