NACA Hood Ducts

[Bill D]

On the originals, they were used for something, but what? And why aren't people using them on the replicas? And could they be made functional?

Thanks
Bill

[Mark Clapp]

They feed air to the cabin dash side vents much like the center one feeds air to the demister grill. One problem with making them functional is you have to come up with a system to drain off any water (rain) you might catch with them and not deliver it into the cabin.

[Bill D]

Thanks Mark

[Tom_Hughes]

And, as Ford found out, it will cost you 78 horsepower if they are configured the way they were initially. It's a great story.

[Tim Kay]

I understood that the two forward naca ducts feed air that channeled through opendings along the inside of the doors through another opening at the bulkhead. At that point I don't know where it was directed. I could be wrong but I saw some cut away pics once that illustrated this.

[F3L]

Does anybody have a diagram of the general set-up of the NACA ducts feeding the various cockpit vents..?

Just curious.

Rick

[DaveWharran]

Bill,
They are functional on ERA's. All 3 tie into the HVAC system.

[Pete.]

[ QUOTE ]
And, as Ford found out, it will cost you 78 horsepower if they are configured the way they were initially. It's a great story.

[/ QUOTE ]

Where can I read the story??

[norman falkiner]

Pete, Ronnie Spain's book I am pretty sure has it. Regards

[Tom_Hughes]

Guy's soory to be like that. I believe Norman is correct. I've had all the good GT books over the years, but could not remember which one it was in. I tried to do some web searches, but could not find it on the web. To use the vents to flow fresh air through the cabin and the seats cost 78 horsepower to drive it (the ventilation). It drove Ford Engineers crazy till they figured it out. Perhaps someone else can post it and give proper copyright credit to the original material.

[Mark Worthington]

I thought the 78-hp loss was for the prototype GT40 bodywork, and that Ford had gotten the aero glitches pretty much worked out by the time the Mk I design was completed.

[Jools]

I belive the reference you are looking for is on pages 32 +33 of the Osprey GT40 The Legend Lives On. ISBN 1-85532-524-1. Hope this sheds a little light on where those 76 horses went! [img]/ubbthreads/images/graemlins/grin.gif[/img]

[Bill D]

Can the non-functional vents on the kits be made functional?

Bill

[Brett James-McCall]

Can anyone lend me the book, I haven't got it yet. Ta

Brett

[Fred/Belgium]

Brett,
I believe I have 2 books.Will come back to you asap
Yr adress?
Rgds
Fred

[Brett James-McCall]

Fred,
You have mail

Brett

[Kalun D]

"Can the non-functional vents on the kits be made functional?"

Sure they can, it all depends how much time and or money you want to spend. I always thought all the ducts should be functional, especially the brake cooling ducts. People invest big bucks in 14" rotors and then have fake cooling ducts that are just creating wind drag. Actually as originally designed the GT40 has a very intricate cooling air duct system, most of the kits don't replicate this as it's not very cost effective.

Fiberglass is not that hard to work with it just takes a little research and time and patience. You can make forms out of cardboard, styrofoam board, foil and foil tape. My "kit" didn't come with any duct work so it's all being fabricated from scratch. The front brake ducts go straight up the side of the chassis to a flexible 3" duct hose that connects to the brake backing plate. Unlike the originals which turned into the chassis and back out to the backing plate. The front brake and NACA duct vents all have connections that allow for the front clip opening.

Another place that causes problems is the spare tire cover radiator vent nostrils. On the originals the air passage through the radiator is totally sealed, all the air that comes in the front goes out the top nostrils. If it's not sealed or if the nostrils aren't shaped properly the front clip can become pressurized and cause wind drag.

The front side NACA ducts go to eyeball vents on each side of the dash and the center one goes to the defrost vent. The large side vent at the back of the doors splits at the vent entrance, 2/3 goes to the rear brakes and 1/3 goes to the engine compartment. The upper side vents behind the doors obviously go to the intake but this is another area some kits fall flat. The intake area has to be sealed so all air coming in these vents goes to the intake. Otherwise the intake gets hot air and the rear clip becomes pressurized also creating drag. This is difficult because it has to provide for the clip opening just like the front.

Pressurization of the front/rear clips has caused other problems. Front spare covers have been known to blow off and even possibly rear clips if the latches are substandard and the pressurization lifts the clip enough for air to get under the front edge.

If your really serious about this you need to find an original car or one of the better kits and take some pictures, believe me you won't remember how everything goes.

[Bill D]

Thanks Kalun.

When I get my kit next year, I will be better able to design a functional system. But thanks for the detailed explanation.

Regards

Bill

[F3L]

Good advice, Kalun. Thanks!

Rick