Large Pickup Aerodynamic Mods

[elhigh]

For starters, those rear wheel openings are gigantic and for the most part have no wheel in them. Even partial fender skirts would do you a world of good up there. If you're never loaded enough to fully compress the suspension on your worst road, then you can really cover those up and not suffer at all. You could probably add partial skirts to the front wheels, too.

You don't have the big HD aluminum wheels with their projecting hubs, so you should be able to find some smoothie wheel covers, for the rear wheels at least. You may want to consider leaving the fronts uncovered for thorough brake cooling. There's an awful lot of room under the truck though, so that may not be necessary. Wheels are great big air churns; at 60mph it takes about 1hp just to turn the wheel against its own air resistance. Reductions there are reductions in the fuel bill.

I bet those openings in the bumper are optional. They're handy for stepping into when working under the hood, but they aren't big enough to add much for cooling. If you're going to start blocking openings, that's a fast, easy place to start.

Pull the mirrors in on the freeway if you aren't towing. The right-hand one for sure.

The step rails are really out there in the wind. Clambering up into a 350 without one is a chore, so you probably don't want to pull it off and leave it off. A longer, contoured model that fairs more cleanly into the rocker panel would probably present less drag.

An aftermarket air dam could reduce how much breeze gets under your truck. BONUS: reducing air pressure under the truck improves the effectiveness of hot air getting out of the engine bay, thus offsetting increased cooling load of blocked-off grille openings.

A smoothie bed cap like Bondo is making. It would look awesome on your ride and keep it fully functional.

Lowering the truck would reduce under-body drag.

A belly pan would reduce under-body drag.

Most of the aftermarket diesel chip manufacturers say their product both increases power and fuel economy - that's worth checking into.

[SVOboy]

^^ Good advice right there,

[Big Dave]

I take it your truck is a 4x4 with an automatic.

For aero mods. here's what I have. They look crude but they do work.

http://www.fokisd.org/gallery2/main.php?g2_itemId=508

[buckyball]

BigDave,

Wow. That air dam is a monster. My truck is a 4x2, automatic, 6.0L diesel.

A few questions, unless there's a link with all the juicy details:

Air dam:
- material?
- what's the slot for?
- what is the ground clearance?
- is the bumper plastic or metal?

On the bed cover (very nice work BTW):
- covering material? (canvas?)
- how many transverse ribs? (pics suggest at least 2)
- more pics on the cover?

Are there any grille blocks - if not was there a negative result from attempting to install them?

Finally, what were your MPG gains?

[buckyball]

Elhigh, thanks for the information. A few questions about your suggestions:

- Would the use of (full) fender skirts on the rear wheels eliminate the need for smooth wheel covers?

Also, by "full fender skirt", I assume you mean a covering spanning the wheel well opening parallel to vehicle's side. Or, do you mean a structure that partially fills in the well reducing the clearance between the well and the tire?

- Agree on the bumper openings (tow hooks, never use 'em)

- Thinking about a clear polycarbonate cover for the fog light openings - have to check the clearance so I don't melt the plastic

- Unfortunately, the mirrors *are* pulled in. you should see them extended

- The leading edge of the step is curved, but probably not in an optimal way, and I agree that it extends rather far out to the side. I have seen aftermarket retractable steps (both minimal per-door and full-length). I am concerned about added cost and weight, but will add that to the list of candidates.

- Agreed on the air dam. That plus grille & bumper blocks seems to have the largest impact on drag reduction, based on what I've read here so far.

- I like the design that Bondo is working on. Unfortunately, not available to purchase as of yet. (Go Bondo!)

- Not sure how to lower the truck without (a) compromising its towing and hauling capacity and (b) spending a lot of money. Open to input on that one.

- A belly pan has possibilities. Simple to implement.

- I am aware of the chip mfrs. I look askance on claims of simultaneous HP and fuel economy gains (unless I misunderstood).

[Big Dave]

Answers for buckyball:

Air dam material is 3/4 x 24 inch wide conveyor belt.

The slot is for my tranny cooler. Yes, a ZF6 requires a tranny cooler.

Ground clearance started at 1 inch but is now 1.5-2 inches.

The bumper is an OEM Excursion bumper with Rhino Lining sprayed on. I recommend that.

Fairing cover material is rubber stair runner, back side out. I needed something that would bend in two axes and it happened to be laying around. It is fastened to the frame with cove base adhesive and drywall screws and fender washers. It has lasted better than I thought it would. It even shrank a little giving me a fair smooth surface.

Two transverse ribs. 3/4 inch plywood.

More pics http://www.fokisd.org/gallery2/main.php?g2_itemId=508

No grille block to date but that is on the "to-do" list. I intend to go whole hog right away and work toward having operable dampers to back off the grille block as the engine/AC get hot.

The fairing is worth 3 MPG over an open bed. The air dam came too late in the year for a fair test. I'm working on a more rounded air dam to push the air side rather that the bluff thing I currently have.

Side skirts and fender skirts are also in the works. I intend to put Mooneyes on the wheels to clean them up some.

Since you are a 4x2 you can consider slamming the truck. Mine has a 3 inch slam up front (plus lowewred another inch by going to 225 tires) and a 6 inch slam in the back. That was good for another 1-2 MPG.

I also went to 3.08 gears. This was a powerful tool, gaining me 2.5 MPG. If you do this you may want to contact Brian's Truck Shop in Arkansas. He builds super performance automatics that can live with a numerically low gear ratio. That ratio will flat kill an OEM automatic.

You gotta figure out some way to defeat the EGR system (if you are off warranty). That robs the 6.0 of efficiency. It is also the cause of many reliability problems for the 6.0.

[buckyball]

Thanks for all of the input so far.

Here's a first pass at the suggestion "elhigh" made to close the openings in the bumper.

Good ole double-corrugated cardboard and clear strapping tape. I covered all of the cardboard exterior with tape after I took the pics, in case we get more rain.

I did not attempt to completely close the opening around the tow hooks. Somebody let me know if that's real important at this stage or not.

A final implementation would need to allow the fog lights (either side of the center opening) to shine through. Perhaps acrylic or polycarbonate...

Also, there is an inlet below the bumper (hard to see w/o my highlight) which appears to flow air past the tranny cooler mounted near the lower edge of the main radiator.

Also, a close-up of the grille. There is not much behind the vertical opening, so I probably close both (L & R) of them. Closing the horizontal openings will require more experimentation to avoid overheating things.

[buckyball]

To follow up on some remarks about the mirrors -

- Yes, they are really, really large.
- They hang out there pretty far to start with (1st pic) and
- Really hang out there when extended (2nd pic)

As the pics show, some effort was expended to make the mount aerodynamic, and the "arms" have an elliptical cross-section with the major axis aligned with the airflow.

The mirror itself, though *somewhat* rounded on the back is still a pretty big drag-producer.

While I'm confident that removing the mirrors would result in measurable drag reduction, I have *got* to have something to replace them with. This vehicle has enormous blind spots; without the convex mirrors (in the lower portion of the mirror assembly), I cannot see a car that is next to me at all.

I have contemplated a rear-mounted (top rear of cab) video camera, as is used in large RV's and Class A motor coaches, though I would obviously like to keep it low-cost, and low-tech often achieves that goal.

Any clever solutions for either modding the existing mirrors or replacements which do not sacrifice safety?

[buckyball]

And if this beast wasn't aerodynamically challenged enough, check out the wipers, which have no recess to hide behind at all.

I've seen at least one other poster who created a fairing for his. Hmmm

[Big Dave]

Yeah. I've got the "elephant ear" TT side mirrors, too. They are an aerodynamic abomination but they are also the best side view mirrors I've ever seen. Without them I'd be blind as a bat to my rear. Clearly CCTV is the long term answer and I'll built pockets into my next iteration of bed canopy for cameras and augment them with tiny Porsche-style side mirrors to keep cops off my butt.

As for the wipers - Lund makes a wiper fairing for Super Duties. I've never considered this a high-priority because the wipers live in a high pressure low velocity part of the truck and with low velocity have little scope for generating drag. You might try the Lund fairing and let us know how it goes.