Minivan Kardboard Kammback boosts MPG +3.7% (6.6%, counting roof rack delete)
 

While Trebuchet03 shows us how to do things by the book with CFD (computational fluid dynamics) to optimize a Kammback shape on his Jetta sedan, I employed the other kind of CFD on my brother's minivan:

Cardboard Fabrication with Ducttape :D

This is a variation of Craig Vetter's CAD process: Cardboard Aided Design

This was an A-B-A on road test under perhaps the most ideal conditions I've ever encountered on my favourite test road. No wind, no traffic, perfectly functioning cruise control :), tight distribution in the results. I'll post the full details later, but here's the skinny:

Vehicle is a 2005 Pontiac Montana, long wheelbase version, 3.4L V6, automatic...

http://ecomodder.com/imgs/montana-pa...boattail-2.jpg

http://ecomodder.com/imgs/montana-pa...boattail-1.jpg

(More photos below in post #20)

This roughly slapped together Kammback, with fairly conservative angles (10 degree plan & roof taper), improved fuel economy by 3.7% in AAAA BB AA results.

If you add in the initial roof rack removal I did to get to the clean roof, the total fuel economy improvement was +6.6%. That's significant, and hopefully may motivate some of you van/trucklet drivers.

Absolutely nothing new here of course. Much attention has gone to studying and reducing the size of the wake behind trucks, since their cargo-carrying capability dictates a boxy profile with no taper at all. Researchers have known for decades that:

Aerodynamic drag can be significantly reduced with trailer add-ons that reduce the wake and increase the base pressure. - Source: SAE 2000-01-2209

Edit: added the following, Nov 23...

Details of the test...

- Test speed: 88.5 km/h / 55 mph
- Cruise control set once, cancelled with the brake pedal between runs; "resumed" for subsequent runs

- Bidirectional averaged runs on a straight and nearly level test route; runs were abandoned & re-run where I was overtaken or caught up to another vehicle (aero interference)

- Wind conditions were perfect: none!


http://ecomodder.com/forum/attachmen...1&d=1227470567

A runs, average of all: 33.72 mpg (US)
A runs, standard deviation (of average of bi-dir pairs): 0.35 mpg

B runs, average: 34.975 mpg (US)
B runs, standard deviation (of average of bi-dir pairs): 0.18 mpg

Improvement of B over A: 1.255 mpg / 3.7%

Roof racks on, Kammback off (one bi-dir run): 32.8 mpg (US)
Improvement of B over roof racks: 2.175 mpg (US) / 6.6%

I approve :thumbup::thumbup::thumbup:

Is the rear hatch still functional?

I don't see how it could raise ALL the way, but looks like it might go most of the way.

Fun project!

Darin's amazing!

Unless, of course, the kammback were attached to the hatch, and sealed to the body with weatherstripping...

Legal implications for the taillights? Most states have a visibility provision in the vehicle code... outlining exactly how much (area) of your taillight must be visible from a given angle... mostly rearward, but I believe they might have something to say about your blocking light from the side/rear-angle view.

All in all, great work though.. and far less intelligence necessary to pull this off, making it a great mod in regard to effect vs. work/thought.

We all like the thoughtless mods... like we don't have enough stress in our lives to add physical permutations of fluid dynamics and airflow based on a given scale to our schedules... roffle.

All in all, a big :thumbup:.. can't wait for updates.

Incredible result :thumbup:
The minivan is so long compare to the Kammback that I would have bet the difference was going to be non-measurable.

It could be interesting to correlate the gain with the rear area reduction.

It could also be interesting to see efficiency difference when the lower part of the Kammback is cut-out at the light level.

(I will have to search again for an after-market cruise control available in France...)

Denis.

6% gas milage increase would be less 2mpg in that thing, thats hardly a deal to have to drive around with that on the back. I'm sorry but I dont feel 2mpg is enough of a savings to deal with that thing hanging off the back. you'd get better than 2mpg savings just driving ecostyle

At $3 gas, 6750 highway miles/year*, 23 mpg = $58 savings. Less as gas drops, more as it increases obviously.

Another note: the speed of testing was just 89 km/h / 55 mph. Actual savings of course increase with speed.

(* that's 45% of EPA's average annual distance of 15k miles total city+hwy)

Which ecomod is better than ecodriving ?

This 6% is granted whoever drives, ecodriver or not.
An ecodriver will have a 6% effort-less bonus, not negligible :cool:

15000 miles at 35mpg is 428 gallons
15000 miles at 33mpg is 455 gallons
Result : 455 - 428 = 27 gallons free and 250 kg CO2 not sent to the atmosphere (see my sig). My son (and I if I'm always alive) will thank these efforts in 50 years.

And this cardboard ecomod is only a test. Done in a more weather proof way, as metrompg and others know how to do it, it could be stealth. My white coroplast front grill block on my light grey car doesn't attire a lot of looks.

Denis.

It was effectively taped shut for the test, but I don't see why it couldn't be designed to open all the way if the lower sides were attached differently.

Oh, yeah, that goes without saying.

This was just a quick 'n' dirty test. A permanent version (my brother has no interest in one) would need proper lighting - lights brought out to the end of the addition is the obvious solution.

right but to build it out of anything even semi permanent is going to cost more than that...

though, 6% is a good number, and nickle and diming works both ways so it could help to lead up to an impressive deal. but wouldnt a small roofline extension and short side extensions give almost all the same benefit? (I felt I should actually add something productive instead of whining about a giant kamma) cause thats something that would more likely be put on more vans an such, a few short little extensions could look cool even

Since $50 is nothing, please paypal $50 to my eMail address (trebuchet03 at gmail dot. com) :D:thumbup:

That said, a few short extensions likely will have nowhere near the same magnitude of effect. Over a 10 year lifespan, $50/year is $500.... And if you get another minvan, odds are that if you built it in the first place, you can adapt it to the new one :thumbup:

Kidding aside

Car Talk

Going from 100 to 200mpg isn't as effective as going from 10 to 11mpg :thumbup: This is why I think we should be using gallons per 100 mile rather than mpg. It's much easier to see the difficulty in sipping less fuel when the asymptote is 0 and not some unknown mpg number :thumbup:

21.5mpg = 4.65 g/100mi
23mpg = 4.34 g/100mi

100mpg = 1.00g/100mi

BOO!!! as much as I enjoy memorizing random integers (3, 5280, 12, etc...) I would still prefer seeing us switch to L/100 Km. I've heard some other countries have already converted to the metric system! haha.:turtle:

I figure it would be better received using an apparently more patriotic British system... oh the irony :p

6.6%
 

Darin,do you think Canada would mind if Washington D.C. used you for the next 4-8 years ? There's a guy headed there,come January 20,'09 that could use you in his cabinet! With 200-million vehicles on the road,all these little 6.6% would mean an awful lot.--------------- Nice goin'! P.S. Does CAD/CAM involve masking tape?

Ha! Phil, I'll only do it if you and several other members will let me put your phone numbers on speed dial! I figure I'd be pressing that button a lot, since there are sharper knives in the EcoModder drawer on this subject matter.

Masking tape would work, but I prefer duct tape for some reason. Maybe I should switch. The duct tape leaves an awful mess behind.

---

FYI, I've updated the first post with the details of the test for anyone who cares.

Checking my calcs, I also discovered a small error that caused me to understate the effectiveness of the mod by a very small amount (3.7% actual vs. 3.6% stated originally).

Hm... 0.1% difference in actual vs. stated.. to the positive. Shoot him!

We all make mistakes, man. :thumbup: on the work though. What would be great is if we could all make something like this for relatives and non-immediate family/friends that looked aesthetically presentable, didn't change the vehicle's drivability, and still had a decent impact on mileage... kinda like changing your friend's light bulbs to LED or Fluoro bulbs when they don't know it.

Is it wrong to mess with your friends by changing the hidden bulbs in their house? I say no. It helps them, it helps the environment.. anyone that could get mad about that needs to get a hobby. Like helping to save the environment! LOL.

Anyway, back to the original idea: IF we could all get something that would aesthetically fit the vehicles of our loved ones, and give it to them for Christmas, it would be like giving the world a Christmas gift - Slightly cleaner air for all! And they'd never know it, they'd just think it was a cool thing for their car to add on.

On that topic (what's aesthetically acceptable), today I was shovelling my car out of a snowbank and a gentleman getting into his car nearby said: "hey, that's quite a 'bonnet' on the back of your car". Referring to the Kammback, of course.

So I chuckled and asked, " you want one for yours?"

He immediately answered "NO!", then smiled and drove away. :)

I wonder what it would take for the average person to see this as a "cool thing".

Hey Metro,

if your giving away kambacks, i would like one for my isuzu npr box truck! would love to see how i could get the mpg up!

i am joking of course, as to the free part anyway its very interesting to me, and i am in awe of the folks that go out of their way to do the mods then take the time to share them! ty !!

No problem - it's very interesting to me too, and fun on top of all that.

A couple more photos, FYI:

http://ecomodder.com/forum/attachmen...1&d=1227479564

http://ecomodder.com/forum/attachmen...1&d=1227479564

http://ecomodder.com/forum/attachmen...1&d=1227479564

I think it's important to repeat that this was a super quick 'n' dirty "fabrication" using the a pretty conservative 10 degree top & sides angle. It could no doubt be optimized for even better results.

But not by me! I've got my own car to work on...

Chrome it... spray it in some candy color fro accents, then add ridiculous lights to it.

Marketing scheme for the new generation.

Found a pic with showing the Kammback from another angle:

http://ecomodder.com/forum/attachmen...1&d=1229133759

When I did the testing, I had placed reinforced cardboard "triangulation" bracing from the bumper to the lower outer corners of the Kammback to fix them in place. Didn't want them flapping at 55 mph.

Why not make the kammack out of plexi? It's kinda cheap, weatherproof, and won't get in the way of the tail lights not being seen as designed

Economy?
 

How are you getting 30+ MPG I have an '01 and only get 21 MPG were you using hyper miler techniques?

This is fuel economy at a steady 55 mph. The tank mpg would be significantly less given starts/stops and freeway driving above 55.

All I know is I am putting this in my things to try in the future file. I take 5-6 thousand mile road trips most every year and a few mods like that will get me another nights hotel. :)

Brian

Kamback
 

Ditto on the things to do list. This is a mod that I will be doing on my'03 Matrix.
Thanks for the post, Bob

hear hear! though.. lets go all the way and make it l/100km!:thumbup:

Mr Miata - you could do a nice tapered hardtop for the convertible as well. I'm sure I've even seen a photo of an aftermarket one. Not going to get much use in the top-down season though.

oops.... guess i shoulda read some of the following posts :o
he he...im new here.

2003protege is right. This was MPG under ideal circumstances - 55 mph, flat road, fully warmed up (and empty) vehicle, zero wind.

Tapered Top
 

MetroMPG The only tapered top I have seen was not removable. I guess i'll have to suffer poor MPG with the top down.:o

Have a Great Day, Bob