If you look at a 964 grille or a 930 lid/spoiler you can see where Porsche engineers decided to increase air flow to the engine and the intercooler, both have angled slotted surfaces that force air into the engine's compartment. Both designs leave the back side of the spoiler (lip) alone, making me think that the best solution would be to install a slotted type grille on a duck tail to mimic the solution they adopted in later models.
http://forums.pelicanparts.com/uploa...1462367116.jpg
http://forums.pelicanparts.com/uploa...1462367128.jpg

Same thing on the 993. If this was enough for their last and biggest air cooled engines, then there is some wisdom in it.
http://forums.pelicanparts.com/uploa...1462367609.jpg
http://forums.pelicanparts.com/uploa...1462367621.jpg

JP, you are right on the RSRs having some ducks. I meant this car, a US 1978.

And if you look at a 964 spoiler in the raised position you will see a rubber skirt sealing of the back area, if I'm not mistaken.

Just for perspective guys, I am not pretending this isnt something to work on. This is the same guy with twin scirocco radiator puller-fans shrouded to the bottom of the supercharged car's intercooler...switched on by IATs....

I have some more open patterns on hand to work with too. I am going to paint them all up at once and can switch between them later.

Bottlecaps for scale.

http://forums.pelicanparts.com/uploa...1462370644.jpg

http://forums.pelicanparts.com/uploa...1462370657.jpg


This is the one I want to try and make work.

http://forums.pelicanparts.com/uploa...1462370754.jpg

Al lkosmal started this thread and sells these grills, I wonder if he can chime in? Have PM'd him too.

How do you like my new grill?

http://forums.pelicanparts.com/uploa...1302488194.jpg

Well, you want as much air in to the engine bay as possible => Leave the low pressure rear of the duck sealed.

If you want some cool "ventilation" (I must admit it looks quite OK) then block it of on the inside.

Regarding Al's grill - I'm using one now and noticed oil temp unchanged using his grill on a duck tail (sans vents) compared to a turbo whale tail configuration. Runs at about 180F.


Sent from my iPhone using Tapatalk

Greetings,
While originally making the prototype for my grille, high priority was to make a lightweight, functional, cool custom grille. I chose the pattern that best matched the stock 911 grille's open area. My grille has just a hair more open area than stock. This was, by design....to ensure that it would flow as much air as the stocker and also to not allow any more rain/moisture to enter than the stocker. (I live north of Seattle...it rains sometimes.) The calculated, open area numbers are somewhere in my original thread.......

http://forums.pelicanparts.com/porsche-911-technical-forum/602269-do-you-like-my-new-grille.html

I would not install a decklid grille that restricted the flow of air.............and I really like the idea and cool faktor of adding vents to the duck...........however, I would not do it if it was a step backwards functionally........ functional cool faktor is....cool.....non-functional....not so much.

I do really like the DIY approach to JohnJl's duck idea and I would press forward with testing to verify if it works or not.

regards,
al

Al Kosmal
the x-faktory
koz@x-faktory.com
RGruppe #669
www.x-faktory.com

The bottom line is that any grill over the engine lid opening poses a degree of air restriction. Whether it materially affects the cooling capacity depends on the operating conditions.

My college prof., upon observing my metal screen carb "air filters" reminded that the restriction is the air intake area less the total area of wire or metal around each air path. Makes sense.

As for the engine lid grill, what isn't apparent is the threshold where a grill design affects the needed air flow. Race cars have a lower threshold than a street car. That leaves a wide range. If engineer-anal, one could coalculate the data as Al did and/or use a manometer and air temp sensor to observe the effects of non-stock grill designs. Without repeatable data, most observations and conclusions are anecdotal and best-guess mods. Fortunately, most mods are performed w/o dire consequences despite being contrary to physics and known engineering practice.

Sherwood