Pickup trucks and bed aero
 

Been looking at the aerodynamics of pickup trucks since I bough an 03 ram diesel last week. The ram 1500 has a tiny little spoiler on it that the 25/3500 series don't, it cleans up airflow and guys claim a half mpg increas from this straight bolt on part. There is also a short flat piece that goes behind the top of the cab and helps redirect airflow over the open box. Supposed to work I can't find real use numbers

Today I saw a truck with a softtopper on it. It's like a convertible top, folds out of the way when not needed. The guy had the sides off, just the top was up and I was wondering if a straight piece of wood might be enough, even curved from the top of the cab slanted to the back of the tailgate.

Second thing I wonder about is the dam in the front, the trucks being so high off the ground what if the dam was more sloped backwards

The chin spoiler really should not be any lower than the lowest thing on the underside which can grab air. My S-10 4x4 has been raised a little by a previous owner, and the chin is about 7-1/2" off the ground.

Chin Spoiler:
Chin Spolier - fast/easy/cheap/effective - Pelican Parts Technical BBS

If you have a cover on the bed, then yes air flow will trip over the top of the tailgate lip. On my older truck I re-directed it there on purpose with a roof wing. Your truck has an arc in the roof which does the same.

Rear Spoiler:
Rear Spoiler on Pick Up Truck - Experiment - Pelican Parts Technical BBS

Roof wing:
http://ecomodder.com/forum/showthrea...1-a-19525.html

From what I've reading and been seeing on pick-up truck wind tunnel pictures, they have addressed many of the issues you questioned. However, one of the wind tunnel pictures of the Ram has been said to be photo-shopped. I have no verification of that, it's just what another forum member claimed/observed.

http://s184.photobucket.com/user/kac...?sort=3&page=1
http://i184.photobucket.com/albums/x...psa9f4225e.jpg

http://ecomodder.com/forum/showthrea...bums-3541.html
http://ecomodder.com/forum/member-ae...truck-aero.jpg

http://ecomodder.com/forum/showthrea...down-9732.html
http://ecomodder.com/imgs/airdam-front.jpg

I bellypanned my 96 diesel, used various grill blocks, and even made a testing aeroshell for it.
The trouble is, I have not run it any significant amount of time to collect data. I had more efficient rigs to drive. When it moves these days it is towing something heavy or large or both.

If you ask me, grille blocking a Diesel is dancing with the devil.

I cannot see how the benefits would outweigh the risks.

Not at all. One of the things about a truck like mine is huge excess cooling capacity.
It was designed for a worst case scenario of making a continuous 180 HP while towing a 9300 pound load up a steep grade at high altitude on a hot summer day.
Real world loadings are paltry, by comparison. I ran it all last winter with NO cooling fan, for example. Then I started blocking the grille off to see what heated up. I have instruments for transmission temps, EGT, intake temps, you name it.
Now I have a couple of electrics that I run on low speed when towing the 5th wheel.
Last week I took it up to 5000 feet on a cool day on Rainier, towing an empty 3500 pound flatbed trailer with the fans turned off.

I stand corrected then.

Yeah, I've run (unloaded) in 100 deg F heat with the grille 100% completely blocked off and didn't overheat the coolant. That requires several other efficiency improvements (EOC P&G and others), but illustrates the point.

I drove a 1986 Diesel Golf from 1985-1990, put 80,000 miles on her (purchased new). At around 60,000 miles it blew a head gasket, which apparently they were known for. Mostly covered by the extended warranty I purchased. It was an expensive policy and an expensive repair - I broke even.

I don't think my electric fan ever went on, even had the dealership check it in the first few months of ownership because I thought that it was odd and perhaps broke.

I'm not going to block the grille on my TDI bug either, I think they run much closer to capacity on a regular basis. The intercooler gets a lot more use than my truck, for sure.
I'll get active grille on the truck this winter (sure I will ;) ).

The grille on that car is already just a lower valance slot, a fraction of exposed area verses traditional looking cars. I would not mess with the Bug either.

Something I have been thinking about re the aerodynamics of the pickup bed. Suppose that instead of looking from the side, we look down from above. Then perhaps cutting a couple of NACA-style inlets behind the cab and louvering or dropping the tailgate would really improve the airflow. Any thoughts?

Sketch it up, I bet someone has pondered a similar thought at one time or another and will recognize it.

How about a soft-topper under a rack? If you did it right it could look like this:
http://ecomodder.com/forum/member-fr...w12-650-16.jpg

There's lots of opportunity in the wheelwells.