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Sayyad 09-01-2008 03:31 AM

Jetta TDI Duct Tape Mods
5 Attachment(s)
I'd like to thank all of you who post your vehicular modifications on this site. You all inspire me. This post is the beginning of my contribution to this community and the humble beginning of my car's transformation.
I used silver duct tape to update the aerodynamics of my silver Jetta, masking off most of the front grilles (leaving the intercooler air intake open), any possible gaps over the front wheel wells and as much as possible of the rear wheel wells. I also tried to make a front undertray but it sort of took itself apart within a few kilometers.
The tape isn't the greatest for this. I had to roll up the edges of the front skirts a bit (but that's okay; easy to do since the inside edges can be rolled in and stuck to themselves) because they rubbed the tops of the tires a bit. I'm also pretty sure the rear skirts got sucked in a bit towards the tires at speed. And the lower front grille block tore open just a little bit along a tape seam at around 400km into the trip.
Which brings me to what you're probably all wondering: did it work? Yes it did.
The car's previous best was around 4.8ish using dino diesel. With these duct tape mods the car used only around 4.3 litres per 100km using B20. Mostly highway, but all the rest was literally spent stuck in traffic, being tailgated by jerks who were really keen on getting to the next red light.
So I think my next move is to make these mods more durable.

tasdrouille 09-01-2008 08:21 AM

Now that's funny. We have exactly the same car. Good work on the car. Keep it up.

FunkSkunk 09-01-2008 07:52 PM

Careful, don't leave that on there too long or else you will have a heck of a time getting the duct tape residue off your TDI.

Sayyad 09-01-2008 08:00 PM

Yeah, I'm washing the car tomorrow and I'm sure I'll have a good time getting all the residue off. Apparently either Goo Gone or equivalent or good old WD-40 should do the job; just don't leave either sitting on the paint for long and wax the car after.

tasdrouille 09-02-2008 07:34 AM

BTW, I blocked the intercooler grill. You'd be surprised how good of a job it still do even without airflow rushing through it. Cruising on the highway at 60 mph on a fairly hot day, my IAT was 110 F.

ChrstphrR 09-02-2008 08:40 AM

On my A4 TDI, I've blocked underneath the valance - so that between the ground and the intercooler, there's not as nice a place to empty out the air that rushes through -- but I've kept that front grill closed.

I would like to figure out a better way - ducting the air out into the fender, perhaps (I'm missing side skirts yet, so intercooler air probably exits out there, but that cavity down by the intercooler is quite big.

A question, since I haven't seen an A3 engine under the hood - where does that model pick up it's air from the front? On my A4, it's on the upper corner of the upper grille.

I was thinking about that when looking at Sayyad's taped upper grill block: About 1/4 of the A4 upper grill feeds the air intake, so when I get to making a block, I won't be blocking that.

Sayyad 09-02-2008 09:40 PM

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The A3 cars get their intercooler air from the lowermost driver's side grille, which has a duct directing all air from that opening (and rocks, and water spray, and the occasional bird) right into the intercooler. You may be able to see the duct and the intercooler at the end of it in the photograph I have attached to this post.
I don't know where the air exits; probably out the back of the front undertray along with the air that passes through the radiator. This probably isn't that efficient but it must work well enough if tasdrouille can block off the air supply and still have low intake temperatures.
Wait; tasdrouille, did you measure your intake air temperature before or after the turbocharger and intercooler?
A3 Volkswagens get their engine air from a hole in the passenger's side fender. This air then passes through a pipe with a few bends, a piece of mesh (the snow screen), a large airbox, the filter, the mass flow sensor and then on to the engine.
Anyway people have been known to drill holes or install a dryer vent grille through their fender liners right behind the intercooler with good results.
I seem to remember that wheel wells containing a spinning tire have low pressure in front and at the back and high pressure at the top and where the tire meets the road. If this is true then placement of the wheel well exit vent would have to be just right. Of course I'll bet the pressures in the wheel well would change completely if it was no longer a sealed area. Anybody have access to a supercomputer to run some calculations?:rolleyes:

tasdrouille 09-02-2008 10:00 PM

I got the temp from the IAT sensor which is past the intercooler. Ambient was 85F that day. Cruising at 60 mph average boost was roughly 1.5 PSI at the turbo outlet. As stated earlier IAT was pretty steady at 110F.

That would be a totally different story if I was putting a big load on the engine, but in my particular case with the way I drive, it does not make much of a difference.

Sayyad 09-02-2008 10:49 PM

That's quite good indeed if it's after the intercooler. I probably don't know enough about turbocharging but a rise of only 13 degrees Celsius through all that piping and the turbo and a sealed engine bay seems very good.

slipstreamer97 09-03-2008 12:12 AM

thats awesome,

I just did the same thing myself. made a full grill block and taped all the crevices and gaps in the front area. On my previous trip from LA to Sac i got 38, this time i got 43. Also employed some PnG as well (as much as you can with an auto tranny).

Good work


Sayyad 09-03-2008 03:51 AM

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Hey Jake. Well done; that's quite the improvement. That generation of Accord looks like it has pretty good aerodynamics, I'll bet with a belly pan and your full grille block you could glide pretty far in between pulses.

MetroMPG 09-24-2008 08:53 PM

A belated welcome to the forum, Sayyad. Nice to have another aero enthusiast who isn't afraid of a little duct tape residue.

NeilBlanchard 09-24-2008 10:55 PM


You know what take off the tape residue? Goof-Off solvent -- I got mine from Home Depot.

On the grill blocks, you may find that leaving some of the lower radiator grill open, and closing off the top opening completely works better for FE. Also, some foam gasket tape (with adhesive on one side, again from your local hardware store) might work very well to seal the hood gap at the front edge. I think this is a critical point, because the air pressure is highest on there.

Sayyad 09-24-2008 11:51 PM

Thanks; I've been reading the threads on here since the site started; I just started posting once I figured I had something to contribute.
I used Goo Gone and my favorite solvent, Elbow Grease, to remove whatever residue remained.
My car needs a paint job. It looks like the whole car was painted with a spray can of silver and a paintbrush of clear coat. Parts of the car always look wet due to the runs in the topcoat hanging down below the lower edges of body panels. The rubber seals around the doors have, on average, 2mm of silver overspray on them. In short, pretty terrible. I don't respect my paint.
Still, be careful when removing duct tape from a cheaply painted plastic surface. I managed to peel little bits of top coat and paint off the bits of the front bumper that were obviously not sanded before being painted (no primer either, as I can now see). Perhaps I should have removed the tape sooner or warmed it up before peeling it off.
On my bumper a few more tiny chips aren't really noticeable beside the rest of the rock chips and paint flakes.
No paint was removed from any metal body panels, and all the remaining tape residue came off easily.
I consider duct tape to be a very useful tool for repairing, modifying or prototyping many things. It has its downsides but a lot of the time cardboard and duct tape are the quickest and easiest tools for simple jobs.
"Keep your stick on the ice."

NeilBlanchard 09-25-2008 06:31 AM


I should've said that the wheel opening covers look functionally great -- they do not stick out any farther than the body, and they cover the critical areas where most of the drag around the wheel openings occur, I think.

Did you put them all on at once (front and back)? I'm contemplating using Coroplast on the front wheels, smiliarly to what you've done -- what do you estimate is the effect of the front mods?

Sayyad 09-25-2008 07:33 PM

One benefit of the tape is that it has a really low profile. It doesn't add any protrusions to the surface of the car.
I was up late reading this site one night and I had found a big roll of duct tape earlier in the afternoon. I applied all the tape to the car within an hour or so in the garage with a flashlight at around 3AM, using a washcloth and a bucket of hot water to wipe any dust or dirt off the car that could have affected the tape's adhesion.
The front wheel skirts are complicated. Look at the third image from the first post in this thread. It shows the partial front wheel skirt. Notice the notch in the skirt's lower edge about halfway along it's length. That notch is from the front tire rubbing against the skirt when some set of conditions are present, perhaps accelerating around a turn while going over a bump.
So if you are going to install front wheel skirts you'll have to figure out the full range of motion of your front wheels to get the size just right, especially if you're using coroplast, which could easily melt. Or you could build a flexible skirt which would work better anyway.
I only know how much of an improvement there seemed to be with all the duct tape on at once. Reducing airflow in and around the wheel wells is always a good thing, so go for it anyway and if you do just the front ones please tell us your results.

ChrstphrR 09-25-2008 10:36 PM


Originally Posted by Sayyad (Post 63455)
The front wheel skirts are complicated. Look at the third image from the first post in this thread. It shows the partial front wheel skirt. Notice the notch in the skirt's lower edge about halfway along it's length. That notch is from the front tire rubbing against the skirt when some set of conditions are present, perhaps accelerating around a turn while going over a bump.
So if you are going to install front wheel skirts you'll have to figure out the full range of motion of your front wheels to get the size just right, especially if you're using coroplast, which could easily melt. Or you could build a flexible skirt which would work better anyway.

I had to replace one of my inner fender skirts in August, and there are a few mounting screws on the Jetta fenders along the edge that could be used to hold brackets that secure a more permanent skirt.

Back on the GasSavers forums, there was a fellow that made a full rubber and Coroplast front skirt. With the mounting points available, I'm thinking that a gap-filling partial skirt for Jettas that covers the top and front edges is feasable.

If only that one portion contacts and wears in the center, then it seems likely to me that coroplast + rubber edged top, or top and front skirt would work. After prototyping, to figure out the right shape to avoid rub points, a more permanent material (ABS plastic?) could be used for the hard portion of the skirt.

My only BIG concern about this approach is how a front skirt will change the fenderwell behavior in winter (since we three Jetta owners commenting in here all live well into the snow belt).

I'm not so sure I want to be a guinea pig for this, because I know the worst situation would be that a front skirt would promot more fender "filling" with snow and ice while driving long distances on the highway... which may fill enough to impact steering.

I'd love to hear any input on the winter situation, either to confirm or allay my concerns.

And on the weekend, I might go and try to snap pictures showing the screw in points on my A4 fenders. I'm assuming there'd be similar points (maybe, possibly identical positions) on the A3 that Sayyad and tasdrouille have.

NeilBlanchard 09-25-2008 11:04 PM


I get the "fender filling" frozen gunk already, even without any wheel skirts. The tire wears it away -- until it melts, or I kick it out of there. I'm not sure that I'll be able to leave the Coroplast mods in place during the winter -- they might fall victim to the weight of the ice?

Sayyad 09-26-2008 01:06 AM

If a belly pan were installed, blocking off airflow exiting from the lower rear of the engine compartment, would the hot air from across the radiator and through the underhood area be forced out along the driveshafts and suspension in the wheel wells? Maybe this would keep the tires warm in the winter. In the summer the extra heat would improve tire traction though it would probably decrease braking performance at low speeds, but all the while would keep air from ending up under the car where we don't want it anyway. Maybe some kind of sliding vent under the car to control where the air can most easily flow.
Something that I really don't understand about cars is why, if they can modernize the interiors and engineer safer windows and better paint and electronic everything, they haven't changed the basic design of the engine compartment. Not just recently; not ever. It seems to me that the engine is still basically a block of metal with dozens of messy wires and pipes, all supported by two metal beams running from the wide open grille to the flat, protrusion-studded firewall. Install a hood and fenders, some kind of bumper, and you have the basic engine compartment design of all front-engined vehicles that I've ever heard of.
Why not build a sealed compartment with variable openings for air ingress and egress? Instead of a flat firewall that impedes airflow, use a panel shaped in such a way as to direct air out hood vents at the base of the windshield. A sealed and aerodynamically optimized engine bay would control component wear by reducing rust and dirt contamination on all those hoses and pipes and electronic bits while allowing precise control of heat and aerodynamics for any driving situation.

ChrstphrR 09-26-2008 05:56 AM

Hrm, I replaced most of the stock plastic undertray with a coroplast one before taking a trip. On the return trip, it was removed by a roadkill raccoon or porcupine (didn't stop to ask what it which one it was).

With just the undertray replacement (like OEM), I found that my water temperature was elevated at highway cruise speed into the high 70s, Celsius -- 74-78, in September, with air temperatures in the 10-20C range, while at 100kph

When I added a lower grille block for the radiator... I found my temperature rose much higher - Scanguage said I peaked at 96C at 110kph (legal limit for divided highways in Alberta), and 85C steady for 100kph.

I'll see about my fenderwells no matter what this year -- one is new as of August, the other is original, and the car was built in late 1999. The older ones are quite rough from all the debris flung up into the fenderwell over 8 years. Maybe the new one is the answer, and I'll get the driver's side replaced before winter. I'll probably try "greasing" the plastic inner fenders with a spraycan of kitchen vegetable oil (a.k.a. PamŽ, but I'll go generic) if I find the newer one has clogging problems still.

Looking in atop and underneath my engine bay ... things are so crowded up. I'm not sure how sealing the compartment will do regarding coolant temperatures. Does anyone know what temperature the cooling system for a TDI can take, until it's liable to overheat? Unless my sensors are out, 80C and 90C from the Scanguage is still safe; 70C and up seems to give better mileage, too.

I'm not sure what the cooling system can take during warm weather. In winter, I'd be much more game to seal things up well, especially since I know I'm headed for some LOVELY -30C and -40C weather this winter. :)

I'm thinking next year, after the snow's gone, I'll be investigating a way to seal up the radiator better, so that there's proper ducting both into and out of the rad. Perhaps exiting the air out to the fenderwells, perhaps out along the exhaust to cool the turbo. Part of the reason to leave it, is to think about the best approach, and to plan trips so I can get enough time and distance to test out any ideas I try ;)

tasdrouille 09-26-2008 09:33 AM

I too fear the coming winter. Especially since I installed my side skirts and went with an even lower airdam. Clearing the slush off the wheel wells will be mandatory after every trip. I might try greasing. I'm even considering taking the bus on snowstorm days. I also fear that coroplast will become extremely brittle in -30 weather.

I do not know at which temp exactly the rad fan kicks in (I think I remember hearing once a bit over 200 F), but it would be important to stay below that temp.

I've haD everything but the top grill blocked in the front all summer long. Stock belly pan under the engine. The temps throughout summer stayed below 200 F most of the time. For the winter I will block the upper grill too for my daily sub 10 miles each way commute, but will probably have to remove it for long trips.

COMP 09-26-2008 01:31 PM

Pam spray on helps with ice build-up

COcyclist 09-26-2008 05:23 PM

ChristphR, Lots of guys at the swear by the metal replacement skid plates to protect our vulnerable engines. I have an A4 Golf in snowy Colorado and recently picked up an aluminum skid plate I'm hoping to install tomorrow. My buddy put one on his TDI New Beetle last winter after tearing his out on snowbanks and ice.

Sayad, It's good to see more modding by TDI guys on this site. I'll try to get my "garage" posted this weekend. Keep up the good work.

MetroMPG 09-26-2008 09:05 PM

I'm planning full front fender/wheel skirts for my car as well, and also live in the snow belt. So I've pretty much accepted that they may have to be only a "3 season mod".

That's the situation for alternator-less driving for me too (because of higher electrical demands in the winter, and less sunlight for solar recharging).

Sayyad 09-28-2008 02:13 AM

The Pam is a good idea. Ice only freezes to the body panels because these panels are below zero. Venting engine air or even some exhaust out the wheel wells would melt any deposits and keep our wheel well skirts clean and flexible. Failing that, maybe some sort of brush that is cut close to the tire to remove slush and snow.
Maybe enclosing the entire wheel well would trap enough heat on it's own. Very little air would be flowing across the brakes or through the wheel wells themselves. I'll bet the air temperature in an enclosed wheel well would stay around or above zero on it's own.
Tasdrouille; those are some amazing side skirts. Anybody who hasn't had a peek at his gallery please do so, it's worth a look. Flat hubcaps, blocked grill openings, low side skirts and air dam; I'm inspired. All you need now is a flat belly pan across the lower edges of the side skirts and air dam and you'll have a super smooth car.
I don't think they make a skid plate for my Jetta, but they're a good idea and they work better than the existing plastic cover. The last time I changed the oil I removed the large cover and the small oil pan cover. It is quite obvious that the previous owner went "off-roading" at some point because the oil pan has some big dents in it. If he had used a skid plate the oil pan would have been fine. Then again I guess it saves me a few hundred milliliters of oil each time I change it...
Evans NPG+ waterless coolant is probably a good idea if you're going to raise the engine temperature. This coolant is, if they're to be believed, far superior and it doesn't boil at any normally occurring temperature. It has no water so it's not corrosive either. Then I'd make sure everything is tuned up properly.

MetroMPG 09-28-2008 08:15 AM

Martin's car pics: Fuel Economy, Hypermiling, EcoModding News and Forum -

ecodean 09-28-2008 05:53 PM

I like what you've done so far Sayyad. You can buy an aluminum skid plate for your A3 from Evolution Imports but it is not as large or aerodynamic as the skid plate I put on my A4 Golf. They are also expensive, however mine paid for itself when I hit a car battery at 50mph earlier this year. So far all I've done is to put lower grill block offs made out of coroplast and held on with velcro on my golf. For a while I also had wheel discs made of coroplast but the velcro could not hold the rt. front disc on for any length of time (I suspect a slight imbalance in the wheel kept causing that disc to be thrown off:eek:) My next mod will be rear wheel well skirts if all goes well.

MetroMPG 09-29-2008 03:40 PM

Sayyad: late notice, but the Ottawa EV group (EVCO) is meeting at the Sci/Tech museum this evening. I'll have the Flea in the parking lot for the meet 'n' greet around 6:30/6:45 if you want to drop by.

I'm sure you'll spark some discussion with your mods.

VWCw 03-28-2010 02:50 PM

sayyad, you're an inspiration. i've had my (gasoline) jetta's upper grille and brake vents taped off for the last two years, but now i'm heading outside to tape up some skirts. thanks for the pictures.

lapeer20m 06-15-2010 08:55 PM

Other than duct tape, how do you guys attach your rear wheel skirts?

VWCw 06-20-2010 12:41 PM


Originally Posted by lapeer20m (Post 179190)
Other than duct tape, how do you guys attach your rear wheel skirts?

AndrewJ's thread starts out on the first page with some good photos of attaching his wheelskirts. it does involve drilling into the body, though; so if you're mainly interested in testing/experimenting, tape works really well. just keep in mind that at speed it will flex inward toward your wheels a bit, so plan accordingly.

Chris D. 09-22-2011 09:46 PM


Originally Posted by Sayyad (Post 57962)
Yeah, I'm washing the car tomorrow and I'm sure I'll have a good time getting all the residue off. Apparently either Goo Gone or equivalent or good old WD-40 should do the job; just don't leave either sitting on the paint for long and wax the car after.

a little gas on a rag will take it right off and not hurt the paint..
10% ethanol :thumbup:

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