Kammback vs spoiler-or both?
 

Attachment 15389hey y'all
which would net the most mpg gain? a spoiler of some sort or a kammback?ill try to post some pics- thank you

I had a detached wing for months that didn't seem to do anything at all mpg-wise.

I replaced the detached wing with a small Kammback halfway through the last tank, and saw about 2 mpg gain. Coincidence? Maybe, it may be just from me getting better and better at hypermiling, but I was never able to reach 60 mpg before.

Kammback or
 

Historically,with the exception to wing-form bodies,the K-form aft-body continues to demonstrate the lowest drag.
*It has no separation
*It generates zero lift
*It's modular.Once you've established the essential Kamm architecture,you can simply add additional elongation for additional savings.
*You will have a blind spot on the passenger side unless you provide for a fenestration there.
*And the new backlight,if part of the roof,will be so steep as to block outward vision.A vertical backlight,with louvered cover has been a repeated solution.
*Rear camera systems are a big plus.

ok that sounds good, i may try and get something mocked up/together tomorrow, would 18in make a noticeable gain? ill post pics when i get something set up. thank you very much

Hey, is that a '65 Dodge Dart? :)

18" behind the backlight? Not so much. It would depend on the fit and finish. Think sail panels, like the Dodge Charger, so you don't lose rear visiblity.

18" behind the bumper? Now you're talking. You could halve the wake.

ok, would it be more effective with a spoiler if i only did 18in? i don't want this thing looking to crazy ;)

Sometimes I'm too cryptic. That was me mocking you for starting two threads in two days on the same subject. Sorry.

Either would help a little. Both could be better; there are other things (lower the stagnation point, spats, skirts, belly pan, rear diverter) that could make as much difference or more.

Again, 18" from where?

And why not? Did you see the Blowfish in the other thread? here's the Stupidbaker:
http://3.bp.blogspot.com/-GgDTTOR4bl...0/DSC_0185.JPG

Pics as promised, i would like suggestions for the rear end and anything else you would do. thank you, you've all been very eye opening

It has a particular style going already, some things might clash like stripes and plaid. Fender skirts and peep mirrors would fit right in.

Things you do underneath or in the engine compartment could make a lot of difference. That deep airdam makes sense if there's no bellypan, but if you smooth out the underside you could trim it. How is it on speed bumps? Shrouding the radiator might be needed. If you have an air cleaner with a snorkel intake, just putting a bellmouth on that will help. See Autospeed.
http://t3.gstatic.com/images?q=tbn:A...Wvd_8FXS-pVPZA

As for the rear: Dodge Charger sail panels? If you built a boattail that covered the stock taillights you could do something like this:
http://ecomodder.com/forum/member-fr...8-images14.jpg

How about fender skirt and a diverter that tie together as a single shape by material or color change; sort of a combination of these:
http://ecomodder.com/forum/member-fr...olds-skirt.jpghttp://ecomodder.com/forum/member-fr...11-silver4.jpg

To get started on the details, ponder this:
http://ecomodder.com/forum/member-fr...venturism8.jpg

My best guess is it says 2-4° is the sweet spot between lift and drag. And little circles are better than little triangles.

hmmmm i like the idea of fender skirts, i can definatly make something work. what about sail panels? coming from the side edges of the roof?, or on the edge of the the body near the tail lights?

sail panels
 

I found a blueprint for a 1968 Dart GTS Hemi online.I looks like your car.
With rough measure,it looks like the aft-body of the car constitutes about 34.6% of overall length and your existing backlight is at 30-degrees to the horizon.From backlight header-to-rear of trunklid you have about 14-degrees of slope.
From Buchheim et al research of fastback cars from 1981,at this length,your backlight would be at about 18-degrees for the lowest drag.
18-degrees occurs about two gas cap diameters behind the back of the gas cap,or about half the length of the trunklid.
Since you have a notchback,we might guess that you don't need any kind of rear spoiler.Your trunklid is already too long,aerodynamically.
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If you extended the C-pillars back halfway across the trunk you'd create the 18-degree slope in elevation.
If you filled in the void with a series of stepped, louvered 'spoilers',you'd capture a vortex inside there.
You'd have some privacy.It would take some load off the air conditioning.And the outer flow should skip off the vortex with a clean reattachment without recirculation into the new recessed area.
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For lowest drag,you'd have to chop your rear quarter panels to create an actual fastback.I don't think you want to go there.
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As to other mods:
*There might be a chance to soften some of the leading edges,especially around the headlight buckets,or fab some plex domes,as CAR and DRIVER did on their 'Crisis Fighter Pinto' back in '74.
*Your A-pillars,drip rails,and recessed glass are a problem but I don't know of an aesthetic solution for that.
*An invisible grille block if you don't have that
*Loose the engine-driven fan and go to electric if you haven't already,or flex-fan,or good thermo-clutch unit.
*Rocker panel extensions,a couple inches
*Extend quarter panel bottoms down even with new rocker extensions
*The rear skirts would be good
*Belly pan with diffuser,according to Carr would cut Cd 0.07.

i extended the rocker panels down at the pinch welds, or is that to far in? but that sounds good i have about a week to get it together before the 2000 mile trip

I'll point back to that other thread, and aerohead's post
http://i1271.photobucket.com/albums/...n12-21-133.jpg

Look for basjoos' Civic. He successfully used two rocker panel exensions, one each at the inner and outer tire faces. It extends behind the rear wheel and tapers into a spat. or skeg.

Make sure whatever you do won't fall off half way. ;)

rockers
 

Going back to the 1982 Trans Am Firebird wind tunnel work at Lockheed Marietta,GM's guys got the rockers flush with the outside of the wheels,and down to where a belly pan would be.The air would have a straight path to the rear,losing no momentum by not crashing into the wheels/tires.
Carried behind the rear tires,the extensions,wrapping around into a rear valance panel preserve the momentum all the way to the rear.Subaru published a drag reduction for their 1986 XT by creating this 'parachute.'

Dart rough numbers
 

I looked through my rat's nest.
*I think the 'naked' Dart is around Cd 0.485.:o
*It's aft-body is about 42% of the A.S.'Template' II.
*An approx. 4.8-inch rear deck extension(4.8" beyond the trunklid) would bring it right to the 'Template',so I'm reversing myself when I say it would be okay to do a serving tray type spoiler.
*At 42% of the 'Template' the Dart has the potential for around Cd 0.192,with all the whistles and bells.;)
*The 1991 GM Ultralite is 42% 'Template',with Cd 0.19.
*The 1956 Dodge Dart concept,by Ghia,registered Cd 0.17,at 63% of the 'Template.'
*basjoos' 2005 AeroCivic is Cd 0.17,at 50% 'Template',with its beautiful wheel integration.
*A 'Template' car,at 63% would come in at around Cd 0.149.

Thanks arrowhead, I've got some thinking to do. ill keep updating with pics as i go

PIC update
 

Did some mocking up/mounting. do you think just the sail panels would help out any? thank you

sail panels
 

I do think they could help.They would forcibly control the 'area' occupied by the turbulence,sculpting the wake behind the roof as it were.
Pickups like the Ridgeline,Escalade,and Avalanche are using them after a fashion.
Lotus has done it.Many of the supercars have used it.
I did it with my CRX and incorporated wings and spoilers into the buttresses to further modify the separated flow.
I would give them some gentle inward plan-taper,based upon the 2D-flow wing section of minimum drag.
Here is the MG EX 181 using it for it's body
http://i1271.photobucket.com/albums/...ntitled2-1.jpg

How wide is the fender to either side of the decklid? That will determine how much you can taper in plan. If you reach all the way forward to the edge of the quarter-window, it will make it easier to get a smooth transition contour and eliminate a visible seam.

With maybe a flat bar across the top of the backlight to tie the two pieces together, and a convex curve to the trailing edge.

aerohead's example may seem a long way from you car's body shape, but notice the flat underside and wheel spats. You could totally do that.

ok, if thats the general consensus ill make some sail panels. are the wheel spats like those straight down chloroplast things in front of the rear tires? whats the best way to cut chloroplast

Best way to cut Coroplast is a knife/razor. If yer doing a straight cut, use a straight edge and only penetrate the first layer. You can then fold it back and cut from there. ;)

If yer doing a curve, just take yer time. You might git better results by making several passes on the cut. :D

I was going to suggest a knife blade or a fine-tooth blade in a reciprocating saw.

Coroplast is popular here, but it is impermanent. Consider PolyMetal or Alumipanel or Omega-Lite. They're all plastic sheets, typically 3mm thick, with enamelled aluminum skins on both sides. Their light as coroplast and as stiff as plywood, weatherproof and can be sheared, rolled and braked by hand (given a floor mounted shear/roller/brake with an adequate throat).

I buy scrap at the local hippy recyclers. They also have polyurethane formed like coroplast.