[beetle1303]

THE FOLLOWING IS BASED ON THEORY AND MAY DIFFER IN PRACTICE. GOOD TO READ AND MAKE YOUR OWN CONCLUSIONS AS TO WHAT YOU WANT TO DO TO YOUR CAR. PERSONALLY I WILL BE USING THE FOLLOWING IDEAS TO EXPERIMENT WITH MY CAR AT A LATER STAGE.

While doing some reading for uni for my dissertation, i made the following conclusions (nothing really new but i have to justify everything...).

Theory 1
Quote" The incoming stream is slowed down by a short duct (diffuser), then passes throught the heat exchanger, and is ejected into a low-pressure area" (p.214 ISBN 0-8376-0142-8).

Conclusion 1
Any duct or opening that intakes air has to be on a high pressure area of the vehicle's surface.
This was written for a front mounted radiator ducting, but some of this applies to all ducting. The diffuser isnt needed so much if a radiator or heat exchanger isn't used, but from observing the rear wing inlets on a 996 turbo (intercooler mounted below the tail spoiler) reveals that the actual pipe's diameter is much smaller from this of the opening and that the pipe actually increases in diameter a bit further downstream.
This is done in order to slow the intake air and make it more smooth flowing before it goes further down

Conclusion 2
The rear quarter window surface on any beetle isnt the place with the highest pressure, simply because it isn't on the same plane as the rest of the side panels. IMO a NACA duct will not use all of its flow potenial if fitted on a rear quarter window.
A Remmele style scoop (position-wise will probably flow better), might be in a better situation but i haven't studied them at all.

Conclusion 3
If you don't provide a suitable exit for the air, there will be NO air coming in.
Its as simple as anything that goes in has to come out.
Assuming the application is an aircooled road beetle, there is no actual point in disturbing the factory engine bay air flow with extra intake if you cant provide the neccessary exits. Here comes the tricky bit.

Most of the race/ hipo guys here know that the beetle's back shape (hump) is a nightmare from an aerodynamic point of view. Best guess to seperate the flowing air from the hump is a small spoiler fitted above the rear window.
Ok, so u fitted the fancy bit. how about the air that has to come in from the vents in order to get into the fan shroud and cool your beloved "money pit" ( just to quote smbd here...)?

Lets assume that the above isnt affected. How can u extract the hot engine bay air? Get creative and dont think of poping your decklid, cause exhast fumes and hot air will come inside and kill your engine. You must provide some ducting to get the air out as well... IMO the best way to do this is the use of some vintage decklid with cresent vents sculptured into it (cant find the pic now...). The vents are high enough to get the LIGHT HOT air into the stream of the air coming from the sides of the car.


The better this is I believe that a cooler intake air will be observed, but if overdone air will be stealt from the fan's intake compromizing stock cooling.
As a result i would go for a flat bottom and NACA ducts placed after the torsion tubes and between the diagonal arm and the torsion plate, since there is enought air coming under the car's body. Then direct the air stream upwards through the rear parcel tray and throught the firewall. then some alu vents riveted on the firewall will direct the air downwards ( where cold air wants to be by nature) and provide the exit though a cut out part of the decklid under a specially made wing ( low-pressure area)

No SKETCES or DRAWINGS will be revealed for this as i might merchandise some of the products of the application so i would like to hold the copyrights for this. There are enough hints for this direction. The ISBN number stated above is from a really good and explanatory book for advanced Aerodynamics that can be bought for about $ 35US. NO offence.
Anyone who has the time and money may use this info and investigate more into this. The reason for doing this is that im looking forward to get into the beetle racing scheme when i finish my Automotive Engineering Designer Degree.


Chris