VW MkIV Aerodynamic Mods (Jetta, Golf)

[NachtRitter]

Thought I'd consolidate a few VW MkIV (Jetta: 1999.5 to 2005, and Golf: 1997 to 2004) aerodynamic threads since I have some interest in that subject

Actually, I could not find any good MkIV Golf threads, so I'd appreciate if others could provide links & pics. I think COcyclist has done some aero mods to his Golf, but was not able to find any related threads.

Since I'm a visual guy, I'm primarily interested in pics with descriptions of mods rather than text only.

While the aero mods are not engine-specific, the TDI seems to benefit greatly from them. The combination of some aero mods plus a taller top gear allows me to get in the 60's mpg for an entire tank (for example, ~64mpg with avg speed of ~60mph over ~975 miles a year ago; see my April 2013 entries).

An excellent starting point for aero mods on any car is the page 65+ Vehicle modifications for better fuel economy - EcoModder.com.

Onward, then, with the MkIV-specific mods, in no particular order.

** deejaaa **
User deejaaa has done some interesting stuff to his getto (Fuel Log):
- Grill block:

- Front under-panel (between bumper and skid plate):

- Rear boxing:


These are all in this thread: http://ecomodder.com/forum/showthrea...ock-26793.html

Deejaaa also posted some images which could be used to sketch out some aero ideas, found in this thread: § http://ecomodder.com/forum/showthread.php/1999-2005-jetta-bora-variant-model-template-23590.html


I haven't seen any rear skirts done on a MkIV, but deejaaa is looking for ideas on how to mount a skirt in this thread: http://ecomodder.com/forum/showthrea...eas-27149.html

** DIY GUY **
User DIY GUY, who is no longer active, has a Jetta TDI (Fuel Log) for which he did a pretty clean grill block:


This can be found in thread http://ecomodder.com/forum/showthrea...air-20580.html

** Deezler **
User Deezler, also no longer active, did some clean aero mods to his Bio Deezler (Fuel Log):
- Grill Block:

- Front under-body:

- Rear diffuser:

- Passenger mirror delete:


All from this thread: http://ecomodder.com/forum/showthrea...read-7868.html

Deezler also tried out vortex generators:

See this thread for more details: http://ecomodder.com/forum/showthrea...rear-8839.html

** Trebuchet03 **
User trebuchet03 did some pretty in-depth flow modeling on his Jetta (which he no longer has):


The thread here has some great discussion: http://ecomodder.com/forum/showthrea...etta-5976.html

Trebuchet03 also performed some aero mods on his Jetta:
- Front tire air deflector:

- Smaller driver's mirror:


Details are in this thread: http://ecomodder.com/forum/showthrea...read-8904.html

** metroschultz **
User metroschultz did some very nice bumper side vent covers and wheel covers for his daughter's car:
- Side vent covers:

- Wheel covers:


Some details are available in this thread: http://ecomodder.com/forum/showthrea...read-1368.html

** NachtRitter **
I've also done a few aero mods to Helga (Fuel Log):
- Grill block:

- Front under-body (combines with skid plate to cover nearly everything up to the firewall):

- Rear under-body (covers from axle back to the rear bumper):

- Currently working on figuring out how to mount these pizza pans to the aluminum wheels:


Unfortunately I don't yet have any build threads for my own projects.

That's all I've got for now. If you have any other MkIV aero mods, please feel free to add below!

[COcyclist]

Thanks for starting this thread. The mk IV Golf/Jetta diesels respond well to aero mods especially the upper grill block. I have a full (bumper to bumper) belly pan but haven't started a thread because I am a Luddite when it comes to posting photos. I do have some in my albums if anyone would like to move some to this thread.

Fuel Economy, Hypermiling, EcoModding News and Forum - EcoModder.com - COcyclist's Album: Belly Pan Install

Fuel Economy, Hypermiling, EcoModding News and Forum - EcoModder.com - COcyclist's Album: TDi photos

FWIW I only use the coroplast nose in winter to protect my grill. I stuffed pipe insulation between the grill bars on the upper grill and leave that in place all year round.

[NachtRitter]

Thanks COcyclist! Hadn't thought to look into your ecomodder album...

Here are the details of COcyclist's belly pan on his Golf:

- Using the rubber inserts under the body as mount points (no drilling into the part of the car that you don't want to rust!):

- And some pics of the results:


- Nice shields on the rear wheel wells



His grill block looks like this:



There are a few more pics of the belly pan and the grill block; see COcyclists link above.

[COcyclist]

In the second photo, I have since covered the cat/con from the skid plate to the coroplast with aluminum flashing with no heat problems over the past three years. The pipe insulation on the lower and the intercooler grills on the last photo are only used in the coldest months.

[deejaaa]

FWIW, i have removed the lower and upper grille blocks and the rear boxed section. i logged 64 2 tanks ago and 59 the last, with the mods removed. not sure how that worked.
i have been thinking about changing the front bumper, sort of like this. (my crude paint rendition)

using expanding foam and fiberglass.

[aerohead]

Hucho was involved in the aerodynamic optimization of the original Golf/Rabbit,Jetta,etc.. The nose of the production 1st-gen VW has almost as low a drag as the 'optimum' nose tested on the car.
Hucho mentions that we ought to focus on the rear of our cars,to reduce or eliminate the flow separation which is responsible for the lion's share of drag.
Here is the 'long-tail' VW 'Flow' body of 1981,with Cd 0.14.You can see that it's nose is nothing remarkable,although it does have a complete boat-tailed rear.

[deejaaa]

Originally Posted by aerohead

Hucho was involved in the aerodynamic optimization of the original Golf/Rabbit,Jetta,etc.. The nose of the production 1st-gen VW has almost as low a drag as the 'optimum' nose tested on the car.
Hucho mentions that we ought to focus on the rear of our cars,to reduce or eliminate the flow separation which is responsible for the lion's share of drag.
Here is the 'long-tail' VW 'Flow' body of 1981,with Cd 0.14.You can see that it's nose is nothing remarkable,although it does have a complete boat-tailed rear.

i've read that here but i am hard headed. i realize it won't make much if any diff on the front so i will focus on the rear. i have the template but am still overwhelmed at the thought of tackling that area.
i would like to see a real picture of a MK4 with some rear mods that work.

[aerohead]

Originally Posted by deejaaa

i've read that here but i am hard headed. i realize it won't make much if any diff on the front so i will focus on the rear. i have the template but am still overwhelmed at the thought of tackling that area.
i would like to see a real picture of a MK4 with some rear mods that work.

Here,VW has pushed the roofline up to the 'Template' for the 1-liter car series.It's truncated,so they pay a fine on drag,but it's below 0.19,not shabby.
It's nose is quite blunt in elevation,although has nice side curvature.
Again,the 'secret' is in the aft-body elongation.
The MK4 would see similar drag.

With additional length we get into Cd 0.15 territory,just as Hucho reports

[ausias]

very interrsting my car that shares VAG A4-platform with your Jetta.
1999 Skoda Octavia 1.9 TDI 110 cv Laurin & Klement Gas Mileage (EcoTxec) - EcoModder.com
with less aeromods and also a taller gear it does at ease 3.3 to 3.4L/100kms long trips of 700 kms. Speeds between 90 to 100 km/h.
but conmute trips and air conditioning and also hw speeds of 120 km/h doesn.t permit to do full tanks under 4.3 L/100km so easy.

what engine dow yo have in Helga ALH 90 cv VE rotary pump? or is it a 90 cv TDI with wastegate turbo? or maybe a PD 101 engine?

[deejaaa]

Originally Posted by ausias

very interrsting my car that shares VAG A4-platform with your Jetta.
(1)1999 Skoda Octavia 1.9 TDI 110 cv Laurin & Klement Gas Mileage (EcoTxec) - EcoModder.com
(2)with less aeromods and also a taller gear it does at ease 3.3 to 3.4L/100kms long trips of 700 kms. Speeds between 90 to 100 km/h.
but conmute trips and air conditioning and also hw speeds of 120 km/h doesn.t permit to do full tanks under 4.3 L/100km so easy.

(3)what engine dow yo have in Helga ALH 90 cv VE rotary pump? or is it a 90 cv TDI with wastegate turbo? or maybe a PD 101 engine?

(1)never heard of that place. your local economy gurus?
(2)what gear, L/kms don't mean anything to me. can kind of figure out km/h, but that's it.
(3) don't know who Helga is either. car has an ALH.