My stupid question

I LOVE GT40- Paolo · 08-23-05, 05:31 PM

I noted in several pictures posted also here, many gt40 have the 3 naca air duct closed on the nose of the car.
Dunno what these are for, think 2 of theme are for front brakes.
and also duno why many keep them closed on cars (probably on originals those are all open.)

Thank u and sorry for the "stupid" question [img]/ubbthreads/images/graemlins/grin.gif[/img]
Paul

Closed ones

Open nacas

Bill D · 08-23-05, 05:42 PM

I believe the originals used the NACA ducts to route fresh air into the cockpit since they lacked A/C. Since most replicas have A/C, having fresh air ducted to the cockpit is unneccessary and cumbersome.

Bill D

**brianstewart** · 08-23-05, 06:00 PM

Yes, the left and right NACA ducts went to the left and right eyeball vents on the dash, the central duct went to the demister grille.

norman falkiner · 08-23-05, 06:16 PM

Most of the replicas do not have their vents "open" as that is the way they come out of the mould. It takes a fair bit of work (cost) to cut open and finish properly,
but looks far better, and more original. All turnkey Roaring Forties have the vents cut out and I am sure so will Superformance cars when they arrive. Regards

Craig White · 08-23-05, 07:01 PM

Brian is dead on, I recently traced the ducts on #1034 and that's how they were run. They actually have ducting glassed into front clip that's the same shape as the ducts, this runs back and where the clip joins main body there is a rubber seal, it then continues into cabin where it is piped to appropriate outlet.

I've just finished cutting out ducts on my DRB, then made enclosures for them. The enclosures on side ducts allow me later to attach back into them under the clip where it can be done without damaging the paint on body. Also boxed the middle duct, but doubt I would bother using it. Norman is right, it's a huge amount of work just to do what I did. I have also had to clearance the the body for larger middle duct as well.

If you want to see my napa duct work, click here to check out photos on my build thread.

A lot of cars local to me just paint the front of duct black and put some mesh on front face. Actually looks fairly effective.

I wouldn't personally just cut out the ducts and leave them open. Wouldn't be so great, for one road debris could come out the ducts and you would also see light coming out of them...not a good look.

Ideally it would be best to duct them properly, but since the car is already complete this is difficult. Since GT40 is being painted, I thought the best compromise would be to open them up and enclose them off, giving me look I want and ability to utilise them later...

I LOVE GT40- Paolo · 08-23-05, 07:09 PM

That is the same I thought....really looks better at all,as in original cars.
It is not possible anyway to open it by yourside when u got the car?
With a simple homework drill maybe u can do that easy.
I dunno...i just ask [img]/ubbthreads/images/graemlins/wink.gif[/img]

Btw..Craig..your car is awesome!! [img]/ubbthreads/images/graemlins/shocked.gif[/img]

Paul

Pete. · 08-23-05, 07:31 PM

Example of duct painted black with mesh insert.

Bill D · 08-23-05, 07:48 PM

I plan on making mine functional when my kit arrives in November.

Maybe I can pick your brain Craig and get some idea(s) about how to go about this.

Regards
Bill

Bill D · 08-23-05, 07:58 PM

Here is the plastic "small" NACA duct from Pegasus Auto Racing supplies. It seems I could cut out the area on the front bonnet and glass in this piece. Then add the necessary ducting into the cabin. I plan on using an A/C system. I haven't figured out how to turn one off and the other on to keep from mixing outside and A/C air.

Lynn · 08-23-05, 08:35 PM

BillD,

On most cars the use of the center duct would require a lot of work to employ. I won't say much beyond that until I take my trip up to Detroit to check out Fran's car in person. (This should happen in the next 4-6 weeks.) But generally a half box with rubber edging on the front of the spyder below the windscreen accepts the back of the duct when the front clip closes.

As for the the two smaller ducts on the front, I formed a fibreglass hose connector using modeling clay as a male mold and then glassed it to the underside of the front clip. (Again, I haven't looked at Fran's clips close enough to know if they have connectors already formed or not; most don't.) I connected hoses to these that go down to front of the foot well. I cannibalized a VintageAir MiniSpaceSaver for my A/C and one of the bits I saved was the demister section. It has two male hose connectors with a damper valve on the backside run by a vacuum motor. An electric vacuum solenoid valve lets me select outside air or none with the flip of a toggle. At the moment the fresh air is not drawn by the A/C fan, but relys on forward motion. However, sealing off the fan intake will not be difficult and is one of those "someday" jobs. The hoses are routed in such a way that opening and closing the front clip is not a problem. See pic below.

(No comments about the rusty brake rotor and tie rod end, please. I have a lot of this that I am still working on which is the result of having sat at the paint shop for a LONG, LONG time. I also have replaced the cheesy white tie strip with an elastic tie that pulls the duct into place when the clip closes. You can see a little piece of the duct behind the vacuum line and above the coolant tube as it traverses over to the passenger side footwell.)

Bill D · 08-23-05, 10:02 PM

T^hanks Lynn.

Your explanation helps considerably. I will get a better feel for what I'm up against once my car gets here. I found that almost anything can be overcome with enough $$$ thrown at it [img]/ubbthreads/images/graemlins/smile.gif[/img]

Ian Anderson · 08-24-05, 05:35 AM

Another Question

If you use these ducts and pipe to an eyeball on the dash what happens in the rain?

Presumably a fair amount of water works through with the air and the driver and passenger ger a shower.

The reason I ask is that I am not initially going the air con route and would like to get a good blast of air if possible without water in the UK weather!

Thanks
Ian

Fred/Belgium · 08-24-05, 07:45 AM

Ian,
spot on when its raining and have water from the centre naca.Most of us have it closed as it gives a good airflow into cabin if properly adapted between bonnet and chassis into cabin but water is the drawback.I closed myne in centre with some rubber seal.
The left/right ones have underneath the body an aluminium shield with a 30° angle downwards for airflow guiding towards the brakes.
Hopes this helps.
Fred

Lynn · 08-24-05, 02:44 PM

Ian,

There are a couple of ways to deal with water. One is to have enough duct tubing that allows the velocity of the air to slow down enough so that the water will drop out. And, then you need a low spot with a drain to allow it collect and then escape (perferrably to the ground :-) One can also connect the duct to a box which does basically the same thing. One of the nice things about a NACA duct is that the amount of water entering it is minimized by the recessed design. Water's inertia will cause the bulk of it to pass straight by the duct.

Regards,
Lynn

Mitch D · 08-24-05, 05:08 PM

I had an MGB-GT in college and it had an air intake directly in front of the windshield just like the GT-40, but the opening was simply an oval intake and not a NACA duct. This incoming air fed into the cockpit and into the footwells. It solved the water issue by having the air duct shaped sort of like a sink-trap. At the bottom of the 'trap' it had a 'drain' with a simple flap of rubber. When enough water accumulated it opened the flap and the water would drain out. Very simple and effective.

Mitch D