I was scootin' around the message board, finding all the answers to all my burning questions when I came across this little snippet regarding aerodynamics:
This was quite intriging and it has been floating around in my brain since I read it.

You see, I have a 1967 Valiant coupe and I'm pretty sure it shares the same rear window and surrounding sheetmetal as the sedans, as well as the Dart sedans.

The reason for my concern is I'm building the Valiant as daily driver with hopefully good economy.

Does this part of these cars significantly affect the aerodynamics of the vehicle so badly as to affect the mileage?

Is the an aero 'aid' I can install, such as vortex generators ala the Lancer Evo?

I'm hoping to stir up some additional thought, comments, and in general expand on this.

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Scott - waywardgarage.com
Why is the rum always gone?

Dusters aren't that good for aero (Miradas and late Cordobas are better). The concave rear window cars are worse, but how much worse I don't think has been quantified in terms of fuel economy. Having the engine tuned properly is much more important. If you really want good highway fuel economy then an early Barracuda is a good choice.

Go over to EcoModder and have a look there at aero mods that work.

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Joshua

Way back in the day....

I put some station wagon wind deflectors on my 69 Dart to help out with snow control. Note the Chevelle SW deflector at the top of the window. The concave rear window would collect snow ....and fill up the trunk space on the car.

Notice another spoiler on the trunk (1980 Aspen SW) that smoothed out airflow off the back of the car.

These spoilers really helped the "aero" on the car...but it was still pretty poor compared to my Early A

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Yeah....Im the one who destroyed this rare, vintage automobile.....

Nope. The '67-'73 Valiant backglass is the same for 2- and 4-door sedans, but it is completely different from any Dart item.
The list of things to focus on (i.e., spend money/time/effort on) runs to several pages of single-spaced small type before you get to "address aerodynamic influence of backglass".

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

I would worry about other stuff first, and you don't have the super concave back glass like the Darts.

Josh, why do you say Dusters are not good for aero? The pointy and sloped tail panel below the trunklid? That would be fixed by a proper spoiler. I don't see that they should be worse than a 1st gen cuda...

Lou

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Home of Slant6-powered fun machines since 1988

The old Direct Connection Chassis Book has drag numbers for some of the body styles. The Duster is poor I believe because the air stays attached at the rear causing drag. As you mention a proper spoiler would help this situation. The early Barracuda (and other early cars) is better because of the smaller frontal area.

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Joshua

New member... First post I drive a '72 4dr dart as a daily driver, been driving it for a couple of years now. 318 got at best - 18mpg, 360 now gets at best - 16mpg. Driving 120 miles round trip per day at near $4 a gallon is starting to eat me up. Needless to say, I've been looking into aerodynamics. In the last month, I've looked at alot of mpg/aero sites.... It's almost overwhelming as to what is out there!

Pollen is falling heavy right now and I've been looking how it's accumulating on the car, kinda like tuft/water bead testing....
I see a definite laminar bubble on top of the trunk lid. See pink wing pics here: http://ecomodder.com/forum/showthread.p ... 209-4.html
That tells me the air off the roof is tumbling pretty hard. Of my three cars the back glass angles are 70 Roadrunner- 25 deg., 72 Dart- 40 deg & 71 Demon- 22 deg. If they had to design a new backlight for the superbird because of observed air tumbling, imagine what that extra 15 degrees of steeper/more concave glass on the dart is causing! So, I believe the part about the back glass in a dart hurting aero. I've always seen rain look stagnant on the Dart's back glass too.
I believe the talk of vacuum at the rear of a car, that the wake sucks on the back of the car if it's turbulent. I used to open my driver triangle vent window and start smelling exhaust. I originally throught it was engine bay fumes but after taking my back seat out once, the smell got worse and I could feel air/exhaust coming forward from the open trunk area. I might be wrong here and it's really a high pressure back there pushing air & exhaust fwd to where I sit in a low pressure area.... I've heard the underside/bumper in the back called a parachute. lol Maybe I will open the cowl vents that put out some strong high pressure air and then compare?!

A-pilar streaking on the dart is interesting as well. I see where the roof trim, non-flush windows (recessed and there's a post there between doors) and the top channel play havoc on airflow. Looks like the air rolls off the A-pilar initially straight and in inline with the car and then gets fanned upwards and downwards on the front window. I say shave those rain gutters!

I experienced pretty bad front lift in the Dart with that cow-catcher front grill too! I raked the car down in the front 3 or 4 degrees (to the point of being visually ugly) and that helped. I was seeing a 2mpg gain from that consistently,but being so ugly to me, I put it back level. If I was going to keep the Dart on the road, I'd experiment with grill blocking and an air dam.
Out of time for this post....

Long story short, I fell in love with the 36 mpg duster stories. Reality set in and now I have a '71 Demon with a SLANT SIX that I hope to get low 20s mpg! I'm a couple of weeks away from it being all ready to go. Thanks to all of you for the info in this site; I did the HEI upgrade, rocker adjustment, timing, you probably name it from learning how to do it right here. So much easier than trying to decode a Haynes/Chiltons! I'm here to help; do my share. Just ask... Ronnie

Well, no wonder why most modern cars have nice rounded surfaces meeting the wind! This is a very interesting topic, and it has been covered by all the major car magazines up through the years, starting with the fuel shortage in the '70s. Using modern synthetic lubes to lower friction, trying to imagine air flow along the car's body - and improving on it - while using your brain to propel the car forward - instead of the foot, will definitely lower the fuel consumption. Think efficiency, an optimal effficient engine burns less fuel relative to the car's speed, an optimized body creates less drag. You have quite a job ahead of you, making a brick acting like a drop, but it is pure fun!
For modifications to your car, the data from testing the F-bodies would be a start, as they tried to overcome some of the flaws of earlier designs in the wind tunnels. I wish I could tell you how to find the data, but I'm sorry, no, I can't.
Good luck, and keep us posted on your findings!

Olaf.

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Aspenized

A BRICK! Somebody told me awhile back that's what my Dart looked like.. haha Back for round 2 on this Aero stuff. Olafla got me to thinking about engine efficiency and I remembered I'd researched BSFC (brake specific fuel consumption) when deciding how to build my Slant. I almost went cross-eyed from all the graphs and engineering stuff! Bottom line, I learned that low rpm causes pumping losses from from the engine sucking on a shut/slightly open throttle plate and then frictional losses at higher rpm. And that led me to lean burn/warm-air intake info about less oxygen available so you'd have to push the pedal more for the same power - less pumping loss.... Man, this stuff just goes in circles!

Rear end gearing. I went round and round choosing a rear end. I have Furd Bullit rims on the Demon (rear axle out of dakota to meet over 6" of backspacing - dakotas everywhere in junkyards around here) and I've come across about every gear available for the 8.25. 2.76 I hear all the time for mpg and that's what I have in the Dart, but I read to take advantage of the Slants torque, go a little higher around 3.23. I went 3.5 (w/ 3spd 904) to try it for now. We'll see how that works out. I'll probably wind up with 2.94.... I have a A500 tranny laying around and too bad Andyf doesn't make those adapters anymore... Hint Hint

A couple of weeks ago, I noticed a definite change in my mpg. I was like what the heck! Everything looked fine and normal. Then I checked the tires and they were all around 26psi. Jacked them up to 34psi and I was back in business. Can't say enough for rolling resistance....

Drafting and optimal speed. Back to the aero stuff, I get the same mpg in the Dart poking along around 2000 rpm/55mph as I do 60-65 mph and keeping up with traffic/drafting. About half of my commute is interstate and if I'm poking, I get passed constantly and left with no drafting help. No, I don't draft tooo close; my brakes aren't good enough to ride bumpers! The Darts 360 sure does start sounding good at about 2300 rpm and up so I like to keep up with traffic. Sorry, I'm a sucker for thumbs up I get and seeing windows rolled down to hear the engine. Anyway, due to the brick features, there's definitely an advantage to playing in the slipstream of other vehicles. I get pushed around alot also, especially by semi-trucks passing me and even when they come up on me from behind. Crosswinds on the bridge crossing the bay really get the Dart acting "flighty". And, it's not like I get mean looks for cruising along getting passed left and right. I think people expect us to drive like a Granny.... I don't think my Dart was made to drive 80mph anyway with all the front end lift and engine rpm/3spd combo.

Aero Modifications. Some of the cardboard/chloroplast aeromods I see people do are just ugly. Boat-tail or Kamback the rear of my Demon? Hell no! Wheel well covers; I think not, even uglier.. Ground-effects and I'm looking too new-school. One guy I saw put a Nascar style splitter/spoiler on the front of his Duster and scraped everything. Adding a go-wing might get a little downforce but that adds drag and could start pulling air up into that parachute of a bumper. A wing and a diffuser might work but now you're looking ricey and cutting up your bumper. Cut off those roof rails and now you start affecting designed unibody strength. Do much of anything to the outside of the car and now you're offending the purists and devaluing the car. Put a cowl hood (or any rear facing scoop) on the car and now you're a chevy lover. lol Block off too much of your grill and you risk hurting your engine from overheating. Golf ball dimpling?! Another Hell no category (although that zig-zag turbulator tape used in moderation wouldn't look as bad). Gosh, what to do? I'm sticking to underbody stuff for now.... Maybe A-pillar covers like the superbird had wouldn't be too obvious and help transition the windshield air. I read you can play with wheel wells some (reducing area available for air to collect around the tires). Look at the Insight's front wheel well rear transition and see how it angles in? Going in circles again.... I say drive your brick and suffer a few mpg for the benefit of the smiles per gallon you'll get!

How do you post pics?

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Gearhead, US Navy electronics
, 71 Valiant S6, 72 Dart 4dr 318, 71 Demon S6, 70 Roadrunner 440, & 55 Dodge pickup

Easiest , most effective. Full wheel covers

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Yeah....Im the one who destroyed this rare, vintage automobile.....

Dusters lose aero because the front end is flat like a mailbox.

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Official Cookie and Mater Tormentor.

Hi RonnieB883.
Loading pics is described in this thread. Basically:
[img]http://www.my-picture-storage.com%20]%20A%20text%20for%20the%20picture%20here[/img]

Just remember: NO SPACES anywhere!

Well, we're waiting for a demo now!

Olaf.

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Aspenized

We have worked on our 69 Dart on the aero package and have made some inprovements. I caint say where but James Longhurst and me made some improvments. The problem with my dart is not the rear window it is the front end witch look like a snow plow . But James knows and we will have a new aero package this year. Thanks Ron








It Aint Over Until I Win

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Yeah....Im the one who destroyed this rare, vintage automobile.....

Im glad you caught my spelling error Sandy because that is all you can do. I doint know why you make fun of me but that is fine. Just doint thread on me. You caint race and I am a Slant racer so you are no threat to me . Sell your totem poles in Canada and say whohupe. thanks Ron Parker









It Aint Over Until I Win