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Old 07-08-2012, 08:30 AM   #1 (permalink)
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Phantom Blot (Spökplumpen in swedish) - '75 Saab 96 V4
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Aeromod of a 1964 Saab 96

Hi! I think this may be (one of) my first post at Ecomodder. I´m a saab 96-freak in Sweden with a 1975 Saab 96 V4 as family car and a 1974 V4 as a eco-project. I also have a verry rusty 1964 "shortnose" two-stroker that in a condition beyond what´s worth saving. My plan is to use bodyparts from the older and more beautiful Saab to convert the 1974 to a 1964.

When making such a Frankenstein´s hybrid, nothing is sacred anymore so why not taking it some steps further? At first sight the Saab 96 may look verry streamlined but from what I have read and studied there are many details to be improved. First of all the rear end slope to steep and the rounded end will cause a lot of turbulence. In the winter this is showed by snow clinging to the rear in a wedge-shaped pattern.

What I intend to do is to straighten upp the rear slope, end it sharply to a kammback and add a diffuser. What originaly look´s like this:
http://www.autospinn.com/wp-content/...-concept-4.jpg

...may end up a bit something like this:
http://www.classicandperformancecar....re.php?id=3388

What do you think? I also have plans for mods of the front and sides but that´s a later discussion efter I have decided what to do with the rear.

/John

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Old 07-08-2012, 11:04 AM   #2 (permalink)
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Sounds good to me, and as long as it's unrestorable, go for it! I'm a big SAAB fan (as you can see by the avatar) so I'll be watching closely.

If you're going to be driving the project in the mean time, go for a front air dam as soon as possible.

As you know, the 99 was based on Wunibald Kamm's principles and offers a sharp break at the rear to cleanly separate flow- much like the Chevy Volt/Vauxhall Ampera are doing now. I wonder if you could make one of those on the 96 that would follow the curves of the body, but with a sharp break at the rear.

First, tuft test it and see where you need to begin on the rear end. MetroMPG has a thread on DIY tuft testing- it's really easy
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Old 07-08-2012, 11:51 AM   #3 (permalink)
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Phantom Blot (Spökplumpen in swedish) - '75 Saab 96 V4
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Don´t worry Sven7, my -64 have floor like the car of Fred Flintstone and every part that is involved in keeping the wheels attached are totaly rotten. Your nickname sounds swedish and if that´s where you come from I guess you know that there are already plenty of well-kept and nicely restored 64´s here. Nobody at the swedish Saab-club web forum seems to feel bad about the comming slaughter. Younger Saab 96 with V4-engine have been converted to "short-noses" (before 1965) before so I don´t feel bad for destroying these nice vintage cars. Now my only problem is time...
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Old 07-08-2012, 12:08 PM   #4 (permalink)
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Now to the project itself, from nose to tail:

I think the front of a 1964 "shortnose" seems to be quite well-shaped for good performance, at least the upper side. Everything is nicely rounded. The front wheels are placed quite deep into the body so the wheel arches can probably be covered a lot more. The big nose-job question is what to do with the air that wants to go UNDER the car?

Sven7, you mentioned "front air dam", please explain! I just read about something called a splitter, -a horizontal sharp "sword" that prevents the air hit by the front from going under the car while the air below the splitter continues to pass under the car without changing the air pressure or introducing to much turbulence.

The belly of a Saab 96 is nice and flat. The last part is actually shaped a bit like diffuser but I´m sure there are room for improvements. On a two-stroke body the entire engine compartement is covered with a smooth floor. The only imperfection is the first muffler placed just behind/below the front bumper, but that can easily be covered as well as the "hole" where the rear axle is located.

The question about what to do with the air that passes UNDER the car worries me a lot more than how to shape the rest of the body. I guess the worst thing I can do here is a modification that will push more air under the car.
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Old 07-08-2012, 12:19 PM   #5 (permalink)
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Concerning the kammback I have read different figures about how to design it properly but I´ve got the impression that a slope of maximum 20 degrees on each surface is a good start. In some places I have read that the teardrop-shape should continue for at least 3/4 of the length of a full teardrop. At other places I have read that the area of the flat end should not be more than 50% of the maximum projected frontal area of the entire car.

If this is a good route to follow we can easily look at the streets to se that few car manufacturers follow this recipie. I guess this can be explained by avreage people not knowing what difference it can make and that most people still would find such a shape too extreme to feel comfortable with.

If I look at the Volkswagen L1 concept car instead I find it almost perfectly following the recipies of Kamm with a nice diffuser. Since they have obviously tried hard to get a one litre concept car (1l/100km) I guess they couldn´t afford to cheat with the body shape just to make it look cool. What we see is probably the naked truth and that is what I will try to copy!
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Old 07-08-2012, 01:36 PM   #6 (permalink)
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Im a Saab guy too. I have my grandpas old '77 99. Its pretty much held together with paperclips and duct tape. I wonder what the cd of a 96 is? Im so glad to see a guy driving old Saabs as daily drivers. Good luck with your project!
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Old 07-08-2012, 02:08 PM   #7 (permalink)
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I found this at Wikipedia: Spoilers on the front of a vehicle are often called air dams, because in addition to directing air flow they also reduce the amount of air flowing underneath the vehicle which generally reduces aerodynamic lift and drag.

Spoiler (automotive) - Wikipedia, the free encyclopedia

I see three alternatives for how to treat the wall of air a car in motion have to struggle:

1: Make something of a 3D teardrop body that is teoretically the best in open air. Close to ground this shape will force extra air under the belly of the car in an already narrow space. This will increase lift and add drag. From the little I know about aerodynamics I see a possibility that a slight increase of airflow under the car can be better than having a sharp edge in the front that will cause turbulent flow under the car. I guess this is when a horizontal splitter may be a solution.

2: Cut the perfect teardop in halves and put wheels under the flat side. Even if the air under the vehicle goes undisturbed such a body will create a lot of lift as it is actually an airplane wing. Some of the air under the vehickle will ofcourse be stirred up by the wheels in some degree.

3: Build an air dam in the front that will showel most of the air up over the vehicle and to the sides. But will it not also create a lot of turbulence under the entire floorpan when air is accelerating through the narrow slot between the air dam and the ground? And will not the lower pressure under the car not only create good negative lift but also increase drag a lot? For a competition car where efficiency is not the primary goal there´s no disadvantage but when the goal is to save fuel we can´t afford luxury such as improved road grip.

If we manage to leave the air under the car undisturbed it will rub against the vehicle, if we try to trap it and make it follow the car it will rub the road. If we change the air pressure under the car the air have to flow faster (but the direction depends on the modifications)

So, what is the best way to treat air UNDER the car? As I see it, handling the rest of the air is only a question of smooth shapes and small angles in a teardrop shape. (with or without the Kamm-back)

Last edited by JohnAh; 07-08-2012 at 02:13 PM..
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Old 07-08-2012, 06:30 PM   #8 (permalink)
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Quote:
Originally Posted by JohnAh View Post
So, what is the best way to treat air UNDER the car?
A nice air dam down to the level of the lowest suspension component, combined with a flat belly pan at that level, but rising up aft of the rear axle.

Small air deflectors in front of the wheels, or even a rounded fairing.

You could also put sideskirts on the car, thus keeping more air underneath it - air tends to spill out on the sides between the wheels.

A boattail shape aft of the rear wheels.
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Old 07-08-2012, 11:20 PM   #9 (permalink)
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Quote:
Originally Posted by JohnAh View Post
Don´t worry Sven7, my -64 have floor like the car of Fred Flintstone and every part that is involved in keeping the wheels attached are totaly rotten. Your nickname sounds swedish and if that´s where you come from I guess you know that there are already plenty of well-kept and nicely restored 64´s here. Nobody at the swedish Saab-club web forum seems to feel bad about the comming slaughter. Younger Saab 96 with V4-engine have been converted to "short-noses" (before 1965) before so I don´t feel bad for destroying these nice vintage cars. Now my only problem is time...
My real name's Tyler but I am 25% Danish and 25% Swedish.

It's too bad to hear about a car in such bad condition but I'm glad you will be giving it the love it needs.

By front air dam I mean this- it's similar to a splitter:

Saab 96 by Kompressed, on Flickr

Even if the underside of your car is not smooth, it will push air to the side, "splitting" it. Usually race cars have a more aggressive version with the horizontal piece you mentioned. We ecomodders are not so interested in downforce, though, so we usually go for the land speed racer look.



On this 93 you can see the spoiler that pushes air to the sides. Smooth wheel covers help that air move by without too much trouble. If you can make UrSaab style wheel skirts you'll have a good start. The photo below is undergoing a tuft test, which I recommend you trying.



While the tufts may show attached flow, this flow may be harmful vortexes due to the sloping rear end. If you make the profile of the car follow this streamlining template and observe the 20 degree rule (15 is a bit "safer"), you should reduce those vortexes pretty well.



Line up the ground line and roof apex... voila!



You want to fill in the blue area up to about the 90% mark. Past that, you see almost no additional benefits. Of course, follow a similar curvature in plan view and try to avoid sharp corners as they are bad in side winds.

Hope that helps!

PS- feel free to post some photos. We'd all love to see what you're working with.
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Last edited by Sven7; 07-08-2012 at 11:25 PM..
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Old 07-09-2012, 04:02 PM   #10 (permalink)
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Thanks for great input! I don´t have much photos to post yet and I´m afraid that this project will proceed slowly. Slowly is on the other hand a good way to get time to think! I have many other (more boring) projects with higher priority. The Saab 96 have a special place in my childhood and the last shortnose model from 1964 is what my grandfather used to drive me in. It´s a bit funny that the "flintstone" car I got for free is not only a 1964 but also blue almost like the one my grandfather had.

Because of this sentimental madness I just have to make myself something that not only looks like a 1964 but also sound like one! This means I will install a 850cc three cylinder two-stroke engine, and that is perhaps not so "eco" in any means...
I don´t think I will stick to a two-stroke for very long, but also with such an un-efficient engine it is offcourse possible to make RELATIVE improvments.

I will most likely build my 1974/1964 hybrid in at least two steps. The first step will be quite stock-ish except for attempts to reduce weigth by getting rid of much of the stuff that is nog absolutely necessary. The car will look almost like a standard 1964 without it´s chrome-bling. This will be my reference to start with. From this point I can then add improvements such as a front air dam and a heavily modified tail.

I guess I have to extend the rear about 1m/3ft to get a functional kammback. This modification vill definitely make our dogs happier but will not result in a too bizarre batmobile... BTW, did I mention that I plan to paint the car in black? :-D

I think I have to start a separate thread about fuel optimization of a two-stroker.

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