My 86 Jetta TD

[scrounger]

Have had it for 2 years.

[8v-of-fury]

Whats.. uh.. going on with the back end there??

Pictures please

[scrounger]

Ah you noticed Jeremy. It's to help recapture the balloon of air behind the car. Better performance and most importantly to get better mileage.  My last fill was 56 mpg.

I made it from pink board and carbon fiber cloth. It is hobby of mine. I'd like to make the shape to be complete but don't want to reduce the utility. The trunk lid still works.

[scrounger]

Here are some more pictures.

[CRSMP5]

lock it, hide it, make so i cannot say what needs said... must resist....

[8v-of-fury]

lock it, hide it, make so i cannot say what needs said... must resist....

Yeah its kinda ugly, so what? lol It does its purpose, and that is what he was after .

[Henk]

I have a standard MK3 golf which does 60mpg, and doesn't look embarrassing 
Surely there are ore aerodynamic cars to chose from if MPG/hypermiling is what you're aiming for?

[scrounger]

Do you really think I drive a Mk2 because I like the boxy styling? It's my first VW and  was cheap with 250,000 miles. You guys getting 60 should be proud. Mine would get in the high 40's breaking just 50 until I did this. At least I am not driving a Kub box on wheels.

[libbydiesel]

The bloke is cheating.  He's from the UK where they add almost an extra quart to each gallon...  60 MPG in the UK is equal to 49.9 MPG in the US.

[scrounger]

Thanks for catching that. Makes mine look like 67m/imperial gallon.

I have tried doing what Wunibald Kamm proposed and has been popular on a lot of new cars. Described as a Kammback, nearly every van or SUV has a small window shade to help the air off the back window.

I used tufts on little rods (chunks of a cattle panel laying around my farm.)  to see where the air wanted to go off the back of the roof. The air went back a few inches and got all turbulent. I used that data to build my first window shade from coroplast. Assured that it would help I remade it in carbon fiber.

About 90% of my driving is with a full load,  I needed to be able to use my trunk. So after consideration, I built the park bench on the back, in front of the point the air was going into a turbulent state again.   Trying to minimize the parachute effect that is one of the biggest source of aerodynamic drag.

The car needs paint and this project is a work in progress so the carbon panels are in primer at present.

I actually like the kubvan as it is ugly.  One would make a nice replacement for my big van.

[nathantheengineer]

I understand your reasoning and feel that any innovation should be applauded.

I have a question though; how is the handling affected at speed? Does it make the car understeer or make the steering floaty?

Cheers

nathan

[scrounger]

If it affects the handling I am not aware of it.

I am running Koni adjustable struts. My tires are Firestone Winterforce 155/80x13, they are just a bit taller than the stock 175/70 tires on there. I run them at 55psi.

As far as high speed handing I really don't know. Entrance ramps and back roads seem fine. I drive a fair amount on gravel and unimproved surfaces.

What I notice is when coasting in neutral it coasts further, noticeably further.

[Blocksmith]

Unconventional to be sure, but I like it     Inspires me to perhaps try a smaller version of the upper part on my rabbit, depending on where the air wants to go as it spills over the hatch. Also, I've read somewhere that the underside of the car, particularly the open engine bay, is a large source of turbulent air and hence drag. I've wondered for some time now it there wouldn't be a significant improvement in the aerodynamics by installing a plate to streamline the bottom of the car, perhaps even the whole underside, depending on one's available time a resources. Thoughts, anybody?

[scrounger]

Yep an under body panel can benefit. I drive on unpaved roads and in winter I felt anything that would trap slush and mud would be more trouble than it is worth for me. If the climate and road were better I think it would work.

Here is an interesting picture that I made showing a rabbit body in a wind tunnel with smoke overlayed on my Jetta.

The rabbit and jetta are nearly clones except for the rear.

Of course if you want the max consider this option.

He gets in the 70 -75 mpg range with a non turbo 1.6.

[Blocksmith]

 

Of course if you want the max consider this option.

He gets in the 70 -75 mpg range with a non turbo 1.6.

Might look kind of funny at first, but it reminds me of this: http://en.wikipedia.org/wiki/File:Porsche_935-78_and_Ferrari_512_BB_Spa_2009.JPG , and if it's a good idea for a racing porsche, it's gotta be REAAALLLY good       And 70-ish mpg is pretty hard to ignore... I just might have to try something that radical at some point, as long as I could figure out a way to retain the use of the hatch. 

That pic of the rabbit superimposed onto your jetta is about what I thought the angles would be like--nice of you to confirm it for me  . Means that anything that works for my rabbit should work decently well if I ever get a mk2, right? Gotta love vw cross-compatibility. I think I found the original pic of the rabbit you might've used; definitely saving all this stuff to my 'useful files' folder.
How do the benefits of modifying the front of the car compare to the benefits of helping out the rear aerodynamics?  Also, has anyone routed air passages through the car to spit air out the back?
I get the feeling that a scirocco would be a better starting point for a super-aerodynamically-efficient build...but, I'll do what I can with my rabbit, and try not to hurt its utility too much. Kinda the reason I got it in the first place, really..

But thanks for the info--this is good stuff.