I will state right off that the goal here is to get over 30 MPG on the highway. I think this kind of goal is no different than the goals the racers set for themselves. You decide you want a kind of improvement, (whatever) and you learn what you need to know, and do what you need to do to make it happen. And sometimes it does. Sometimes it does not, or sometimes things break, or sometimes it is worse. But, this kind of challenge is sort of what keeps man waking up and going out to play in the world.

So, with that said, one area of significant improvement in all cars is that of aerodynamics. The faster you go, the more important it becomes. At 55 MPH the air stops splitting easily and starts getting pushed down the road with you. At this speed it becomes even more important to get the air around the car easily. Ask any motorcyclist, and he will attest to the importance of a fairing up front for highway travel.

The bottom of the cars is one area some manufacturers pay considerable attention to, and others do not seem to. Fr our purposes it can be done without making a major change in the look of the car. It is interesting to see which do and which don't. My BMW and my earlier Miata both had very smooth undersides. But I see cars out there today where little attention seems to be paid to this. I looked under a Lexus SUV yesterday and was surprised at how nothing was done to shield the protrusions.

The easiest to improve is under the front end of the A body cars since the lower control arms, radiator core, and sway bar mounts stick down quite a bit below the bumper. Bill asked specifically about the rear wheel well liner I installed, and I will address that now, but will talk about the front later, as that, while time consuming if done right, can be attractive and provide considerable gains. Lou Madsen has run comparisons on his cars and nets a minimum of 10% on everything he has added a front spoiler to. His first one was just a test mule made from a cut up old trash can.

(Breakfast just got announced. More later).

Back from Breakfast:

To fair in the undersides of the rear, one must also fill in the rear of the rear wheelwell, which are wide open on Mopars, mostly owing to the leaf springs, which do present a challenge. While at the junk yard last week I picked up the rear wheel well liners from a Cadillac Seville, which are on the rear of the well. They tuck in behind the wheel opening lip and extend around and are screwed to the inner "frame".

To apply this piece to the Dart I had to trim it down considerably. It is about the right width, but way too tall. I also built a small sheet metal box and attached it to the Dart's frame member to extend the frame out, as the frame rails on the Cadillac are wider, and closer to the wheels, again owing to the Caddy's coil springs vs. the Dart's leafs. I continued to trim a little at a time until it fit over the leaf spring and tucked inside the wheel well opening lip just as it did on the Caddy. I had to cut a notch in the top edge of the plastic liner to go over, (under) the pinch weld on the Dart that connects the inner wheel well to the trunk floor. When I had it all fit nicely, I screwed the piece to the box I added to the frame side, and the inner wheel well near the quarter. I finished it off with a pair of mud flaps taken from an Accura. I had to fashion an aluminum extension down from the new liner to fill in a gap there. I could have left the plastic liner long enough to fasten the mud flap to, but I wanted a more robust material to take the sheet metal screws for the mud flaps.

I have continued to examine pretty much every car that drives by to see how they have handled the various parts of the car to improve the aerodynamics of the lower parts of the car. Almost all cars have a small tab that sticks down right in front of the wheels to break the wind there. Some of these are just pieces of angled plastic, and others are molded into the lower valance and lower pan. Seldom do cars NOT have front spoilers of some kind. Some round down smoothly, while some point forward like splitters on a NASCAR racer. I suspect the NASCAR racers do what is best functionally at first, and then auto designers copy this as a style element to some extent. After awhile NASCAR's rigid rule makers dictate the look. Some front spoilers go all the way out beyond the tires, while others end well inboard of them.

There is much on line about this. There is one article that someone, (I think Ed) posted a link to several years ago where a guy took on the project of improving the undersides of a Prius. There is much interesting info there.

I will detail the front end work in a later post. Now, out to finish the project. AFter today the week gets busy, long and hard.


Sam

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Sam, we all enjoy following your quest for aero improvements and MPG improvements. Can you post pictures of your work. It will go along great with your write up! I am having trouble picturing some of this in my pee brain!!



Rick

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2 Mopars come with Spark plug tubes. One is a world class, racing machine. The other is a 426 CI. boat anchor!

12.70 @ 104.6

Thanks Rick. I went to take photos and the battery was dead in the camera. I will post a few as soon as the battery is charged back up. I hope my pee brain can remember how to post a photo.

The front is just about finished now. I think the big gains for the front have been gotten. Further work will produce less and less. I could make the dam lower with a splitter, but there are too many speed bumps in these parts. Any further gains would seriously change the look, such as on Will's Cuda, which is beautiful, by the way. I am not going there. This car should still look fundamentally like an old Dart.

Sam

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Great !!!

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2 Mopars come with Spark plug tubes. One is a world class, racing machine. The other is a 426 CI. boat anchor!

12.70 @ 104.6

Looking forward to images of your work.

Mrs. Wjajr's Nitro does have not a particularly air flow friendly underbelly. Its tires are housed in plastic wells like most modern vehicles to reduce large openings, but not as well finessed as it all could be.

My 300 has a large panel covering the underside of engine and good bit of the front suspension bits, and complex front air dam as part of front bumper with integral ducting to cool front brakes. Floor panels are flat with drive shaft tucked tightly within a tunnel connecting IRS, and rear wheel wells are somewhat over sized due to AWD lifted suspension, rear space behind rear tires is filled with organically shaped mufflers that have all smooth surfaces. Over all its underbelly looks to be fairly air flow friendly for a big old American tank.

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67' Dart GT Convertible; the old Chrysler Corp.
82' LeBaron Convertible; the new Chrysler Corp
07' 300 C AWD; Now by Fiat, the old new Chrysler LLC

Lets see if this works. Photobucket has changed their process.




Here is another.



close up with flash.


Sam

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It's working!

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2 Mopars come with Spark plug tubes. One is a world class, racing machine. The other is a 426 CI. boat anchor!

12.70 @ 104.6

Maybe my brain is the size of two peas. Look back, there are two more. I will start another thread for the front air dam and lower pan.

Sam

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Hmmmm, interesting!

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Casually looking for a Clifford hyperpak intake for cheap.

Bill, Could you post a few photos? That would be enlightening.
Sam

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Take your pick of articles

http://www.autospeed.com/cms/search/ind ... .x=21&.y=8

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

Ed to the rescue once again. Great sounding articles. Thanks!

Sam

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Nice retro fitting of Caddy parts. Did you incase large opening behind wheel well?

This car sits an inch or two higher due to AWD than a RWD 300C; oddball size stock 225/60 R18 tires allows for larger standard brakes than RWD C come with:



Hard to see horizontal brake cooling duct flush with lower front valance, also a small round cooling hole that I’m not sure just what it is for:



Smooth removable underbelly cowling directing air flow past oil pan, and area between front air dam/bumper to cross member under radiator:



Back edge of belly cowling directing air flow past steering rack under fire wall to flat floor of front foot wells:




Passenger side to driver’s floor mid car notice how drive shaft, exhaust system is tucked up out of view:



Looking Right to Left side at front of IRS, notice fuel and other lines neatly tucked up in channel:




Center rear to front of car, square housing is fixed differential, spare tire well has fin like stampings directing air to base of rear fascia, left is organically shaped rear muffler tucked up into space behind rear wheel and quarter panel:



Drivers side to right side under trunk area showing mufflers, and spare tire well in relation to rear bumper fascia:

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67' Dart GT Convertible; the old Chrysler Corp.
82' LeBaron Convertible; the new Chrysler Corp
07' 300 C AWD; Now by Fiat, the old new Chrysler LLC

Thanks Bill, Those photos are worth a thousand words for sure. I appreciate the time it took. Thanks again for posting them. I have read a ton on the internet since first posting, and here are a few generalizations I can make about the drag that is not upper body work:

1. Nobody knows for SURE what is best. There is limited research. The cooling system and engine present 30% of the drag. The tires roughly 30& and the bottom of the car is everything else. The big deal then is getting the air to come back together on the rear of a square car.
2. The DETAIL design with the least drag in a wind tunnel does not necessarily translate into a car that travels down the road with less drag because it all come together behind the car with considerable turbulence, which is one of the major causes of total drag on the road.
3. Some deigns improve handling, and some improve mileage. Sometimes two are at war with one another.
4. If the bottom of a car is smooth, such as Bill's the most efficient thing to do is direct the air flow under the car. If not, the best thing to do is direct the airflow around the car. The air dams that direct the air under can be identified by the rise in the center, or openings in the center of it.
5. Getting the air to come together smoothly behind the car is the hardest thing to do.
6. The rear spoilers that sit on the deck lid are for mileage. Those that are raised are for handling.
7. The raised ridges on the rear lower valance which are parallel to the travel of the car are attempts to get the air to exit smoothly. They are kind of like subtle vortex fixtures.
8. Skinny and low rolling resistance tires. Skinny creates less turbulence around the tires. Tires account for between 20 to 30 percent of the drag on the bottom of the car.
9. The Germans seem to have spent the most time and money researching this. VW has been into it for 50 years.

There are several things that have been proven to increase mileage in controlled testing.
a. Lowering the car.
b. Putting a full front pan on such as on Bill's 300.
c. An air dam of some kind. Previous considerations apply.
d. Blocking off the grill to allow only the air needed for cooling to enter. BE CAREFUL here. Both this and the lower pan can induce overheating. I think this is might not be applicable to our cars, since the fronts are so flat, and air is not going to go around the front end easily as an alternative to entering the radiator. Getting the air out of the engine compartment and intergrated back into the airflow around or under the car seems the challenge.
If properly applied, the little tabs in front of the wheels can improve mileage, but if the wrong shape or in the wrong place, things get worse. Serious wind tunnel testing is need to get it right. Copying a known effective design would be a good idea. I think those items get down to nit picking.
e. Rear spoiler attached to the deck lid that extends slightly past the flat area of the rear.

At this point in my thinking I would say the big gains are to made in applying an air dam and creating a full front pan. Mopar kind of was onto this idea with the early 70's designs that incorporated a lower valance below the bumper.

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Interesting stuff there Sam.

My son has been driving the same 2.7L 2000 Intrepid since 2003, and constantly gets mileage in the high 20s low 30s, and probably another good candidate for study. Intrepid was one of the slipperiest large cars on the road that predates the pedestrian blunt front end mandates that have spawned today’s pleather of flat faced conveyances.

The rear of the Intrepid is high with a short trunk deck ending with built-in air handler nose, and rounded tail end that I suspect cuts drag by better introduction of side air flow into low pressure area directly behind tail of car. Of the late 90s cars Intrepid was one of the first to sport wheels flush with slab sides to smooth air flow.

Short of grafting on aero parts from a 70 Daytona onto an A body there is not much that can be done for body shape, and duct taping fender skirts on, this only leaves modification to below front bumper & engine, and inner wheel wells; a brick is a brick.

Now to Bing what Red Green has to offer for shade tree aerodynamic improvement of old iron… LOL
Actually old Adolf and his auto engineers copied this.

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67' Dart GT Convertible; the old Chrysler Corp.
82' LeBaron Convertible; the new Chrysler Corp
07' 300 C AWD; Now by Fiat, the old new Chrysler LLC