Making a minivan more aerodynamic.
 

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?

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.

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.

wife
 

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!

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.

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
http://i77.photobucket.com/albums/j5...ay/Corsa03.jpg

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

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.

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.

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.

On that little van I'd first see to it there is no luggage rack sticking out. Then, no mudflaps.

Ride should be slightly nose down. If it's level or nose up, lower the front a bit.

Grille block for sure. A full one probably is too much tho'.

Air dam or belly pan? One or the other, maybe both. Should help some. The wife wouldn't see any belly pan.

Maybe a cowl panel over the wipers would help.

Skirts? Meh. Do it if you feel like it, but I wouldn't expect too much from them

Other than that, just adjust the nut behind the wheel. Since the frontal area and Cd isn't too awful bad I would expect higher fe from that thing. Keep it at 55 mph or less.

i'm not sure how effective the fairing is on the corsa, it's more to show that potential aero stuff can blend with the existing bodywork.

the reason why i think i relative short add on might work is that the back of the vehicle has these rounded edges that where widely used in the 90's. potentially these edges might cause the air to separate at the wrong angle adding a small lip spoiler at the top (as is very common on a lot of current hatch designs), and at the sides you might be able to control the separation angle.

I've noticed that a lot of the newer aerodynamic cars have sharper edges on the rear, which I read in here somewhere helps to reduce turbulence, as lunar mentioned. I've wondered whether adding a border around the rear perimeter to create a sharp edge might not look cool, as well as reducing the turbulence. If I were to make it out of Plexiglas, the tail lamps would still be visible as intended. And I'm thinking a Plexi part kammack would look good also.

I'm going to include some pics soon as I can upload them to the internet.

Shade Tree,
hate to derail an aero thread but Frank is right
at .35 Cd - and mixed driving - aero is not your first concern
(if you were long hauling at 75mph - that would be different)
look for a draggy break set up or mechanical issue
air up the tires and coast a bit - drive mello

then come back to aerodynamics - but don't expect much
aero is finesse and many mods with many small gains
better just to sllooowwww down
I would bet 40mph is your sweet spot - based on CAFE standards
instrumentation (scan gauge etc.) is very helpful

and way easier than a driving backwards :)

From what I'm reading, .35 is very low for such a large vehicle. I'm wondering if the weight of the vehicle (nearly 2 tons) isn't partly to blame. The engine is a fairly old design (it still has a distributor and 2 valves/cyl.) and it revs fairly high in overdrive. It spins about 2400 rpms at 65 mph. But the engine size is quite small @ only 3 liters. I might have some tuning issues, and there is a dragging brake caliper, but I'm averaging 22 mpg, in mixed driving, which is close to the EPA est for highway driving. I'm thinking maybe some of those new iridium spark plugs might help. They sure did wonderful things for my friend's truck. A warm air intake would be fairly simple to pull off, but my van tends to octane knock awful easy as it is.

My wife and I only accelerate heavy when necessary, otherwise we keep the rpms under 2800 or so. I'm trying to remember if advancing or retarding the timing helps low end torque....

Either way, we live in the Ozarks, which is quite hilly. There are a few places we can put the car in neutral and coast at speed from gravity.

Before I drop the aero ideas, would a belly pan help much, or should I just shackle up the rear a bit?

Advance the timing in 2deg increments. If you check it it might be lower than factory spec anyway. When I had my Mustang 5.0s we would dial in 14deg initial instead of the factorys 10deg. On an 87-95 5.0L 36 degress total was what we were going for. Not sure if its the same on a Nissan motor. I know if you go to far you will need premium fuel to stop the knocking. Wich would take away from what you are trying to do. I always ran regular at 14deg with no issues. It has be claimed to give better mileage and a better burn. My right foot was too far in it 90% of the time to notice any savings lol

On that motor I would go with the Denso brand Iridium plugs for sure.

Dean

now to buy a timing light. Haven't needed one since '03 as all my vehicles had coil packs

Yeah seriously.. I know the feeling.. When I threw mine out I felt like I lost my puppy LOL

FYI, drag coefficient (Cd) is independent of size (design constraints notwithstanding). The better minivans have drag coefficients of .30, eg: the original Pontiac Trans Sport / Chevy Lumina vans, Toyota Sienna.

But total drag is Cd times frontal area, and yours is smaller, so you may still be ahead.

Have you seen this thread?
http://ecomodder.com/forum/showthrea...-6-a-6069.html

I know you started this thread to talk about aero, but I'd have to say before I spent a moment or a penny on mods, I'd get instrumentation. The easiest & fastest gains will come by modding your driving style, and you need feedback to do that best. Your garage entry doesn't show any fuel economy instrumentation.

Fuel economy instrumentation? I do have one very important one, espacially for a vehicle with an automatic tranny that loves to downshift-a tachometer. according to revised epa estimates for my van, I should be getting 17 mpg mixed driving, while I'm getting 21-22 mpg fairly regularly; a 25% increase. My wife and I not too long ago were getting 19 mpg out of a 91 ford explorer, so driving economically is not foreign to us.

While a mpg meter would be nice, I've had one before, and I know get into top gear and staying there is the key, as well as gentle application of the throttle and keeping the revs as low as possible nets the best fuel economy. And letting the van coast in neutral on the downhills brings up economy. I know this because I idle @800 rpms while I coast at much higher rpms.

Remember, I live in hilly country, so the 2 tons of steel come into play more than in flatter country.

I think part of the reason I'm pressing on the aero issue is that the average speed limit for this van's regular route is around 50 mph. That may not be 70, but that is a consistent amount of higher speed, and from experience I know the van struggles to maintain speed while staying in overdrive when even the slightest hill is introduced. That and some of the factory plastic "belly pan" under the radiator has since been misplaced on the highway somewhere, leaving a flat brick right in the way for the wind to hit. So I suppose I'm wanting to restore the original aerodynamics and maybe improve upon it a bit.

I know this may be an aero thread, but I appreciate other comments. I plan on getting a ScanGauge when finances permit, and I'm planning a 4400 mile trip in the future, so anything I can do beforehand to save me a buck is money in the bank. I know the earliest version of the villager had a partially blocked grille, because it had a light bar in place of the wide open grille I have now. As much as finding that older version of the grille is desireable for maintaining a stock look, a mod of my current grille is likely to be cheaper. I like basjoos's philosophy: I won't do it unless I can earn the money back fairly soon in gas savings. And unfortunately, even the open source mpg meter mentioned on this site is around $60 to buy, and right now that is 2 weeks worth of gas.

you are on the right track
 

ShadeTree,
you are doing great and your wife is on board too :thumbup:

you are right on with a lot of what you are doing
but a couple of comments

this might not be true
even with lower RPMs - the in gear config could be running on virtually no gas
because the wheels are turning your engine for free
depends on how your vehicle is set up - I do real well In gear
need some instrumentation to know for sure

Besides I'm scared of accidentally "missing" neutral and dropping it in Reverse or Park at highway speeds :eek:
one mistake like that would burn a bunch of gas money

I like the aero stuff too but...
50 mph is not prime aero territory because drag is a velocity squared thing
it is not 30% more at 70 than 50 it is actually doubles from 50 to 70
so you can basjoos the van config or... just not drive 70

Whoa! - new data
you are not at factory .35 Cd - you are more brickish
how big is your "brick" and what cavities opened up with this damage?
belly pan may be worth while if you have a barn door open

Grill blocks are a double bonus
aero and higher engine temps quicker
depending on your van and it's set up this could also be significant
my milage is pretty bad until the engine is warm
grill blocks are so amazing, I wonder why they have such honking big grills at all
but don't over do it - cooked engines are not efficient

Amen

BTW
go for the new plugs and wires - good maintenance and good for FE

Belly Pan
 

My wife and I just went on a long trip... 1662 miles! Before leaving, I installed a belly pan over the engine compartment and one at the very back of my car. I also installed a half grill block (the passengers side) since there was no radiator on that side anyhow. I also installed a windshield wiper block. The result? I can't say for sure that it helped FE (since I don't do a lot of 65-75 mph driving) but I suspect it did. I can however say with certainty that the car was MUCH quieter! My wife and I could listen to the radio without it being super loud, and we could talk (not yell) to each other. Best part, the belly pan is completely invisible, and until I told the wife that I had installed the belly pan, grill block, and windshield wiper block... she didn't even notice.

Cd 0.35
 

The 1922 Klemperer"minivan" achieved Cd 0.16,something which would push your mpg to 27.5 mpg on the highway if your getting 22 now.It's rather amorphous in appearance,with windshield hard to distinguish from rest of forebody.The shape is proven although requires everything from the B-pillar rear to converge along the ideal teardrop taper path.Pretty radical.Short of that though,it's difficult to achieve any dramatic drag reduction without lengthening the van.Virtually all your drag is behind the van in the wake.At one time,Chrysler advocated a vehicle with inter-changeable roof sections.This would have helped out,as a fast-back style roof would have allowed for significant drag reduction,albeit ,with some sacrifice to interior volume.Parking issues make a boattail extension problematic for daily driving on vehicles with significant rear overhang.

I always wondered about the Aztek- if that fastback roof led to any aero improvement at all vs. the virtually identical minivans. Couldn't find Cd values and fe values are the same as for minivans :confused:

the aztek was indeed radical....makes me wonder what they were thinking

As far as how much of a brick i have hanging down below the bumper, its not like i can see it from a close distance, but if you look down, the transaxle and engine drain pans are definitely hanging down below the bumper (there is no factory air dam, like you would find in some other vehicles). And while the inside noise at highway speed isn't unbearable, it certainly is there. This old girl also has a solid rear axle hanging in the way that I'm thinking no amount of shackling can fix.

I'm going to get those iridium plugs ASAP. With it having a distributor instead of a coil pack, this van needs all the help she can get.

as far as a boattail, I wonder why a partial boattail wouldn't help my wannabe aerodynamic brick push through the air a bit easier. While playing with the aerodynamics simulator, a partial kammack on the top and bottom seemed to help. I've noticed there seems to be no mention of a kammack on the bottom of the rear of a vehicle. Why should the back bumper be less important than the roofline? On the Prius, I've notice what looked a bit like a splitter on the bottom of the back bumper. Anyone else figured that out? I think studying the aerodynamics of new vehicles should be a big part of this site. Let the bigwigs spend the money, while we copy them for a lot less

ShadeTree,

copying OEMs is a double edge sword - often what looks like aero work is just styling
I believe it was the chevy volt that had lower drag going backwards - be careful what you copy

as for boattails
you are right - a partial will work

http://ecomodder.com/forum/showthrea...-6-a-6069.html

but the bottom of the boattail is not as important until you clean up the belly
the top and sides have much higher velocity and less disturbed air
thus a boattail/Kamm back have more effect there

But it is not worthwhile to inconvenience your wife for 3.7% FE boost
especially if she is already on board - don't loose your ally

boattail
 

An 18-inch boattail added about 4-mpg to my VW van.The van did not have much rear overhang to begin with and with the tail was pretty easy to live with,although some parking was completely off limits to me.Along with a full bellypan and rear wheel skirts,the kit netted me a 28% mpg improvement.----------- Every 10% wake area reduction = a 10% drag reduction and 5% mpg increase at 55-mph.That will give you some numbers to chew on when contemplating a tail.Both Kamm and Korff recommended that a car be chopped off at the point where its wake was 50% 0f its frontal area.

hmm, 28%? That's really good. For my van that would put me in the range of maybe seeing a 30 mpg tank once in a while. You wouldn't have a picture of your tail, do you? Were you still able to use the tailgate? I can see how having the bottom of a boattail properly built could add some much needed luggage space in a somewhat cramped van. With it being only 18 inches, I'm assuming it was open at the end.

I'm toying with how to do rear wheel skirts. My rear tires are not underneath the van very much; about 1/3 of the tire surface above the floor is exposed. So i may have to think about flaring it a bit before a skirt would do any good.

VW van
 

The project was for college and unable to anticipate results, I fabricated everything over the existing hatch with an enclosed tail over the hatch area,completely losing the rear utlity.The bottom was open with a secondary vertical engine door allowing access to the original door via a tunnel.Since its an air-cooled engine I wanted to maintain any pressure inside the engine bay from the side ram intakes.--- In the future I will lose the rear hatch and extend the bed platform into that space,creating an opening hatch as part of the new tail enclosure.The "tunnel" underneath to the engine will have illumination for after dark servicing.--------- I have photos and will bring next weekend to scan and email to ecomodder.------------- For your application,it would be nice to do a swing-away mount,like a spare tire holder on a Jeep.From the curb,you could un-fasten and swing the tail away for access to the hatch.And in a perfect world it would be carbon-fiber epoxy,weighing only a few pounds.Mine was sheet aluminum over a cedar skeleton,screws,angle-brackets,pop-rivets,with plexiglass backlite.The compound curves I cheated on,slitting the aluminum to bend over the curves and duct-taping the difference.Really primitive.Foam sculpting and composites solves this problem.While mine was "closed" a neighbor built an "open" boat tail for his Vanagon and carried lawn furniture an light things inside.Sepp has done some study which revealed that an open back loses you a little but overall,you still achieve a drag reduction.

I'm thinking the way I'd like to do it is have the floor of the boat tail built out of fairly sturdy stuff, such as steel or aluminum framing and expanded metal floor, with some sheet metal underneath for aerodynamics. For the bit around the edges and top I'm thinking Plexiglass, so i wouldn't have to worry about rewiring lights and such. I may have a light frame going up from the floor to help immobilize the plexi.

I'm thinking about convincing the wife that a closed in setup would be better anyway, since she would have much more room for luggage and groceries and what not, and we can just work around losing easy access to the 28" of luggage space we currently have behind the back seat.

Plexi over the lights is still illegal. Gotta have 'em out back, not covered by anything.

picture
 

ShadeTreeMech,I went ahead and posted a new thread entitled Phil Knox's aero-modded VW Van.Al Glidewell here at Copy-Pro was kind enough to scan the images and do the PhotoShop work to get them on the internet here at EcoModder.As you will see from the images,the thing was just cobbled together but the air liked it enough to reward me at the pump.Hope the images help.

Renewing old flames
 

Wow do I have some catching up to do!

Around the beginning of September of last year my motor finally went kaput. Make a long story short I got a heckuva deal on a used motor and off she goes again. I haven't been as thorough checking the MPG as i used to be, but it still gets over 20 mpg usually, and this engine had 70k on it when I got it. But the van doesn't struggle up the hills as bad as before with the worn out engine.

I'll need to get some more updated fuel economy figures for the ole girl, but it isn't driven nearly as much now since my wife got her a Maxima. But I'm glad to be back on here, and hope to do some research on a fairly ambitious project I have in mind for an EV--namely, making my Explorer electric. Yes, I know, it's huge. But it's practical for my area. But that's for another thread.