Making a minivan more aerodynamic.

[Concrete]

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

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

Originally Posted by ShadeTreeMech

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.

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
one mistake like that would burn a bunch of gas money

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

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

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.

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

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.

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

I like basjoos's philosophy: I won't do it unless I can earn the money back fairly soon in gas savings.

Amen

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

[wyatt]

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.

[aerohead]

Originally Posted by ShadeTreeMech

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?

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.

[Frank Lee]

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

[ShadeTreeMech]

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

[Concrete]

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

[aerohead]

Originally Posted by ShadeTreeMech

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

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.

[ShadeTreeMech]

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.

[aerohead]

Originally Posted by ShadeTreeMech

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.

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.

[ShadeTreeMech]

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.