AJ brake duct hose size

pmason · pmason's Garage

Could someone that has the AJ Brake cooling setup measure the size of the hose?
My car is in the shop right now and I can't just go out and measure it, and I need to order some longer hoses as I'm putting on a new bumper.
Check the AJ/USA site but no specs or details on the hose.
Thanks,
Phil

ShakinJoe · 09-12-2009, 05:51 AM

2-1/2"

ShakinJoe · 09-12-2009, 05:52 AM

it should be 2-1/2 inches.

pmason · pmason's Garage

Joe, Thanks, I've been actually reviewing your light weight thread, great thread, currently in the process of doing the bumpers on my, putting the 74 RS bumper on and want to hook up the hoses to the front now.

ShakinJoe · 09-12-2009, 07:27 AM

Thanks for the comments. I am not sure what bumber you have but you might need an adaper to go to 3" which is easy.

sszakats · 10-02-2009, 09:16 AM

Hey Joe, talk to me about the adapter. My inlets up front are 3". The rotor end is 2.5". How, where, and with what do I transition from 3" to 2.5"? I am considering fabricating my own plastic tubes to mount to the a-arms...like I saw somewhere on this forum. Gonna search for it right now. Thanks, Steve

moneymanager · 10-02-2009, 04:10 PM

try pegasus. Or anyone selling air inlets.

ShakinJoe · 10-02-2009, 05:20 PM

Quote:

Originally Posted by sszakats

Hey Joe, talk to me about the adapter. My inlets up front are 3". The rotor end is 2.5". How, where, and with what do I transition from 3" to 2.5"? I am considering fabricating my own plastic tubes to mount to the a-arms...like I saw somewhere on this forum. Gonna search for it right now. Thanks, Steve

Steve,

I am doing this this weekend fabrcating aluminum tube ducts for the car. You can see PVC and Aluminum on the following thread. Smart Racing Products also carries the brake duct kit like this for around 150.00 if you are not feeling adventurous.

Carbon Fiber Brake Ducts finished

sszakats · 10-05-2009, 04:28 PM

Joe, i already have aluminum aj-USA 2.5" ducts with the strap-on scoops. So the plan is to reuse the ducts but reroute the hose to 3" bumper inlets. Can a 3" hose be clamped to a 2" rotor duct? I realize I am creating a botleneck of sorts, but I sick and tired of ripping those cheesy scoops of my control arms. Steve

pmason · pmason's Garage

Well this Saturday Installed the new duct hoses from the new front bumper. Then preceded to do a track day Sunday and another one today (Monday).
Having to route the hoses under the A-arms there has to be a better way, they took some punishment, both ended up with a hole.
Going to look at something like the other thread with a PVC pipe.

ShakinJoe · 10-06-2009, 06:03 PM

Quote:

Originally Posted by sszakats

Joe, i already have aluminum aj-USA 2.5" ducts with the strap-on scoops. So the plan is to reuse the ducts but reroute the hose to 3" bumper inlets. Can a 3" hose be clamped to a 2" rotor duct? I realize I am creating a botleneck of sorts, but I sick and tired of ripping those cheesy scoops of my control arms. Steve

Steve,

Let's get the terms right first!
The duct is the item that straps under your a-arm.
The modified Backing Plate is the item that brings air to the back of the rotor.

It sound as if your bottleneck is at the point where you need to attach it to the 2-1/2" spot at the backing plate. Use a reducer and it should make this job simple.

BertPage · 10-06-2009, 07:42 PM

Quote:

Originally Posted by pmason

Having to route the hoses under the A-arms there has to be a better way.

There is:
Brake Cooling - different apporoach

This shows an installation on a 964. I think it would be fairly easy to simply go through the inner fender well on a 911 (there is no box section on the earlier cars) and straight into the spindle duct. The fans could be moved back to shorten the hoses.

The ducts that run from the nose and pass around the suspension link with PVC pipe are very marginal. There is very little flow through them to the spindle.

sszakats · 10-08-2009, 11:00 AM

Quote:

Originally Posted by ShakinJoe

Steve,

Let's get the terms right first!
The duct is the item that straps under your a-arm.
The modified Backing Plate is the item that brings air to the back of the rotor.

It sound as if your bottleneck is at the point where you need to attach it to the 2-1/2" spot at the backing plate. Use a reducer and it should make this job simple.

Sorry for the terminology. I need to connect a 3" hose to my existing 2.5" backing plate. What I can't seem to find is this "reducer". Can a 3" hose be safely clamped to a 2.5" backing plate?

Steve

ShakinJoe · 10-08-2009, 11:08 AM

I have not tried that and it might be tough to do as there is wire in the hose designed to help it NOT crush down. You might get one one of these.

http://porterfield-brakes.com/product_info.php?productID=28

BertPage · 10-08-2009, 11:12 AM

Quote:

Originally Posted by sszakats

Sorry for the terminology. I need to connect a 3" hose to my existing 2.5" backing plate. What I can't seem to find is this "reducer". Can a 3" hose be safely clamped to a 2.5" backing plate?

Steve

The transition into the 2.5" opening is going to hurt your cooling air flow. You should try to increase the dia of the entrance into your back plate. And/or you could add another smaller pipe on your back plate to feed off the 3" pipe to make up for lost area because of the 2.5" opening.

You don't have very much flow or pressure thru the 3" hose so at every point in the system where you reduce the area you are also lowering the flow of air - even if the car is moving over 100mph.

ShakinJoe · 10-08-2009, 12:07 PM

I would think the pressure would increase at the backing plate opening at the reduction...no?

Same flow with reduction in area equals increase in P.....

JP911 · JP911's Garage

To reduce the 3" hose to a 2.5" fitting you can simply remove a section of the wire from the inside of the hose. This worked well when I needed to adapt the larger fittings on 993 heat exchangers to my '74, which has 2.5" fittings for most of the heater ducting.

BertPage · 10-08-2009, 01:55 PM

Quote:

Originally Posted by ShakinJoe

I would think the pressure would increase at the backing plate opening at the reduction...no?

Same flow with reduction in area equals increase in P.....

In those ducts you have very little pressure and any change, crimp, turn, etc. reduces flow – even if you are using a fan. You can easily demonstrate this. Example:

KTL · 10-08-2009, 01:59 PM

3 in. hose is indeed nicer, but it creates more problems for an already existing problem- tight confines above the A-arm and ground clearance below the A-arm

I run 2.5 in. hose on my Carrera with IROC narrowbody front bumper. With a stock underbody sway bar, it forces my cooling hose (which is routed THROUGH the A-arm cross-brace via a PVC tube like SmartRacing makes) to hump over the A-arm more and it gets squished against the chassis tub when the suspension travels. I have 23mm front torsion bars, so my suspension travel is less than a stock-sprung 19mm front spring. However with the A-arm through-tubes, it GREATLY helps with ground clearnance. I have no problems with the underside of the duct in terms of ground clearance or debris/off-track excursions causing damage to the hose. Again, where my hose damage occurs is due to the hose atop the A-arm contacting the chassis tub during suspension compression, thus getting a little bit smashed.

I think the key is to use 2.5 in pipe for the A-arm through-tube. 2.5 in. is not a common size and you have to special order it. So for now I am using 2 in. PVC pipe that has some foil tape wrapped on the ends to increase the diameter. You need to increase the diameter because the wire inside the 2.5 in. hose only allows for a little bit of compression when you tighten the hose clamps. Too much compression and it badly crushes the hose and it won't clamp onto the pipe properly.

Nonetheless, I suggest sticking with 2.5 in. hose from the bumper all the way to the cooling plate, with 2 in. or 2.5 in. intermediate A-arm through-tubes On my IROC front bumper, I used a 3 in. to 2 in. plumbing reducer/coupler like this

The 3 in. end is connected to the backside of the bumper via the hose clamp on the coupler. The 2 in. end of the coupler is of course smaller than the 2.5 in. hose. So I sliced through the side of the 2 in. end of the coupler to allow me to insert the 2.5 in. hose INSIDE of the 2 in. coupler end. Works very well, despite what many would say is a substantial bottleneck in the system- the 2 in. PVC through-tube. Bottleneck it may be, but it's WAY better than no cooling at all......

I can shoot some pictures if anybody's interested.

ShakinJoe · 10-08-2009, 03:29 PM

pics would be nice