Making a minivan more aerodynamic.

[ShadeTreeMech]

Bit of a newbie here, so excuse any newbie comments.

My '97 Mercury Villager would seem to have the perfect recipe for an economical car; it's decently streamlined, has a smaller v-6 with overdrive made by Nissan, and it is more compact than most vans. But it weighs in at nearly 2 tons (between 3800-4000) and despite using hypermiling techniques, we can barely get past 22 mpg in mixed driving.

It has a drag coefficient of .35, which doesn't seem terrifically terrible, but i suspect can be improved on. My first order of business is a belly pan, I think, but I'm having to argue with my wife about anything that can be seen. I've convinced her that a partial kammack wouldn't be too bad--Toyota's Prius has one, as do a lot of newer cars. But I'm not convinced that a part kammack will work unless it becomes a bit large.

While looking at the Prius, I noticed what looks like an air dam in the rear. Suppose it's like a part kammack for the under car air flow? Playing with the airflow video tool showed that a part kammack on top and bottom would seem to help some, but my guess would be they would have to stick out about 2 foot from the rear of the van. Don't know if the wife would appreciate that much. I might get away with it if I make the bottom kammack sturdy enough to strap a cooler to.

Something else I confirmed with the airflow video; a minivan is quite a bit more efficient going in reverse than going forward. In reverse, the hood would act as a kammack, and the video shows the airflow being much smoother. Too bad that mod was so difficult to do.......

thoughts?

[donee]

Hi ShadeTree...,

Wheel dams would be a good add-on. Also, take a look at the new Chrysler minivan. It has a little extension off the back rear of the box.

[RobertSmalls]

Stand up to the wife! Start with the underbelly and gap seals, then add an attractive (black or clear plastic) partial grille block, and maybe someday she'll let you install some rear wheel skirts.

She should be proud to drive a vehicle competently modded by her husband. If she can explain the reasons for the ecomods to her friends, she shouldn't worry about being seen driving it.

[aerohead]

Originally Posted by RobertSmalls

Stand up to the wife! Start with the underbelly and gap seals, then add an attractive (black or clear plastic) partial grille block, and maybe someday she'll let you install some rear wheel skirts.

She should be proud to drive a vehicle competently modded by her husband. If she can explain the reasons for the ecomods to her friends, she shouldn't worry about being seen driving it.

You could tell her that she can tell her friends you'll be buying her a very large diamond with the savings on fuel.She might get so excited,she buys you some power tools!

[elhigh]

Rear wheel skirts would be a great addition. If you have any kind of bodywork skill at all, it shouldn't be too hard to prime and color the skirts once you've got them made. Do a nice job and they'll look almost factory - and when you hit that state, you know who sees the mods? Guys. If it looks factory, 99.44% of all women will never ever notice it.

Under your van is a topographical nightmare. A bellypan is totally invisible, but will yield real results.

[lunarhighway]

i'd say work from the front to the back. investigate a grillblock perhaps a wiper shield as the hood looks as though it would lead the air right into the wipers... not a disaster, but things can always be smoother.

a front understray and wheeldams are also quite easy and effective, but a small airdam can work too

a kammback would work too and it wouldn't have to be all that big, it could take the form of a custom spoiler with side fairings

like this for example

[ShadeTreeMech]

ok, air dam vs belly pan........

a belly pan is heavier, but there is no doubt in anyone's mind that it would reduce drag and reduce the amount of road noise.

An air dam is much lighter, but I could see how it would be less certain whether it does any good

has anyone compared air dams to belly pans?

ps that part kamm on the corsa is severly sweet

[/I]I need to do some research on wheel dams

[lunarhighway]

airdam vs bellypan depends on how bad the underside is and how big the actual bellypan can be...fairing over the entire bottom will obviously beat a small strip underneath the bumper, but can be difficult or impossible to pull off... since the engine compartment is the main problem, fairing over most of the engine bay is a good start, provided everything beyond that is somewhat clean. on the other hand a well designed airdam is also good and can improve over the stock situation. It doesn't make the air disappear however so it'll have to push it somewhere else... a to big an airdam can be a source of drag itself, some of the better airdams are lower in front of the tires and curved to the side to guide the air around the vehicle, and a little higher in the center so they allow the air to go easier under neath (where it would end up anyway)

for inspiration you could look at more modern vehicles and see how low their bumper/airdams go and how they're shaped.

[Bicycle Bob]

Most air dams are intended for down force as much or more as for drag reduction. The consensus seems to be that if you have substantial ground clearance, it is definitely better to use a belly pan and leave the frontal area alone.

[Sunwapta]

Would the "custom spoiler with side fairings" be very effective? (As shown in the little blue Corsa pictured above.)

From what I just read on Kammback on Wikipedia is that the tail area has to reach about 50% of the car's maximum cross section to maximize the effect. But hey that might be purists speaking - whereas even a 20-25% effectiveness on a minivan might make it worthwhile.