Don't Underestimate An Air Dam
 

Up until now i thought an air dam was just one of those things that work for racers but not the average Joe.

Normally this time of year, my tankful MPG drops to the high 23s and low 24s. It is 18 degrees and my last tankful with my air dam was in the low 25s. Only difference is the air dam.

Using conveyor belt meant I could be fearless about road debris and get really aggressive about approach the road. I set mine one inch above grade. Yes it did drag on braking but not for long. the road ground off the excess and since all dragging happened during braking or backing up, the "grinding" process did not affect my MPG.

Good to hear.
I've been thinking of making a big front air dam myself. Seems like it could take care of several thorny issues in one fell swoop. (That and COZX2 has one :D)

Could you say how wide (high) this air dam is? And what your ground clearance is now.

Has anyone drove along side to see if it is being bent back by the wind?

How about a pic? ...just saw your pics...now that's an air dam.........

5% gain?

Questions you might want to answer..........


Maybe you can get a gig plowing roads this winter? I used to do that with my sports car with plastic lawn edging.

:thumbup:

Pictures? I want to see this.

Pix. I am somewhat challenged in getting pix posted but here is a link that shows the air dam and my "fastback fairing.

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

Both are engineering prototypes. I am working on better-looking versions for next year.

My air dam (after some grinding by the road) has a 1.5 to 2 inch road clearance.

It does bend back a little (<1 inch) in the wind and also ripples like a clarinet reed. By putting a bend in the air dam I can stiffen it up.

When the snow flies, the air dam comes off and spends the winter in the my garage.

That thing is a monster.

Just the height of that bumper is almost as high as my civic...

Nice results!

Nice work!
I like the cargo cover too!

For pics in these posts, copy the pic's link address and then click the mountain scenery logo in the message building window. That gives you a place to paste the pic's address. You can post multiple pics in one post.

https://www.fokisd.org/gallery2/main....serialNumber=2
Big Dave's Snowplow Air Dam

25MPG from a fullsize! What'd you make the airdam out of? I have lots of things I've been planning on trying and can never get to but now I really need to increase MPG a bit.

Did you consider making it taller and blocking the grill a bit? I wouldn't mind increasing how quickly my engine heats up.

Also is that last picture the inside of the 'fast back'? I had thought a pop snap tonneau type cover/fast back like that would help a lot, I was planning on adding snaps along the cab too and not leaving any gap. Did you try making this without a frame? That is can you just stretch the material tight and get close enough? Any shrinking/stretching/billowing I would think would line up with whatever the air is doing anyway.

How much of an improvement did you see with the fast back? I was hoping for quite a bit, the reason mine got put on hold is because I didn't want to spend $100 for the tool that puts the snaps/rivets together and don't know anyone I can borrow it from. Plus my material is more like boat canvas, I wouldn't want it for winter use anyway.

Hey, your the guy who was in diesel power. I read that article last fall.

You can buy caps for trucks and tonneau covers for trucks, but you cannot buy a fastback cap. The closest thing I've found is a cap called "Top Gun" made by a company called "Snugtop" It has a rounded rear, and should improve mileage quite a bit. But they don't make one tht fits my Ford Super Duty!

It really torques me off that you can't buy aero parts for pickup trucks. I'd buy reasonably priced pre-engineered fatback tops, air dams, wheel spats, mirrors and the like. But the just don't make them. It's a conspiracy, I tell you.

Looks like you have named your market and should start building some...$$$

Is your F350 a 7.3 or is it a 6.0? The 6.0s suck generally, and suck fuel specifically.......

Danronian posted;
?Just the height of that bumper is almost as high as my civic...?

Big Dave sez:
You must have one low-down civic. The top of the bumper is 24? above grade. It looks taller because I slammed the truck 4? to reduce aero drag a couple years ago.


Itjstagame asked:
?What'd you make the airdam out of??

Big Dave sez:
24? by 5/8? conveyor belt. Very, very durable stuff.


Itjstagame asked:
?Did you consider making it taller and blocking the grill a bit??

Big Dave sez:
Nope. One thing at a time. I have taken the OEM grille off and am fabricating a reduced-intake area grille to replace it. Mark 1 version will be a simple blocked grille. Mark 2 will have a damper assembly so the thing can open up at low speed (<15 MPH) or if the engine gets hot).


Itjstagame asked:
?How much of an improvement did you see with the fast back??

Big Dave sez:
3.0 MPG over an open bed.
1.5 MPG over a flat tonneau.

Lovemysan posted:
?Hey, your the guy who was in diesel power.?

Big Dave sez:
That?s me.


Sludgy posted:
?The closest thing I've found is a cap called "Top Gun" made by a company called "Snugtop" It has a rounded rear, and should improve mileage quite a bit.?

Big Dave sez:
It?s better than a square back but not much. A square back makes your pickup a vrtual van ? the ultimate aero brick.


Sludgy asked:
?Is your F350 a 7.3 or is it a 6.0? The 6.0s suck generally, and suck fuel specifically.......?

Big Dave says:
It is a 7.3. Last of the forged conn rods.
The 6.0 gets a bad rap because of the EGR. If it were mine, I?d clean the EGR valve and disable it closed.


Sludgy posted:
?I'd buy reasonably priced pre-engineered fatback tops, air dams, wheel spats, mirrors and the like. But the just don't make them. It's a conspiracy, I tell you.?

Big Dave says:
My next big project should interest you. I gotta get some bucks together because this involves stuff I can?t do.

I?m gonna buy a junkyard Super Duty bed. Mine is in too good shape to cut up.
The plan:
1. Remove tail gate
2. Move the tailgate posts in to being 49? apart (just outboard the inside of the wheel wells) and shorten them to 12? high (they are currently 24? above the load deck)
3. Narrow and shorten the tail gate to 49? wide by 12? high.
4. Taper the bed, starting about even with the rear axle down to this narrowed and shortened tailgate. Essentially tapering the bed both 12? vertically and 30? horizontally.
5. Make a permanent top. For the first foot behind the cab, staying flush. The second foot tapers down about 3? and has pockets for faired-in rear view cameras and a brake light. From there it angles down at a 6:12 pitch to a point about 6? behind the tailgate. The final part of the bed is covered by a tambor door tonneau (truck guys will recognize ReTrax or Pace Edwards) set at the 6:12 pitch instead of flat.
6. Fair in the rear part of the frame and blend it into a roll pan.
7. Modify the narrow/lowered tail gate to make a Kamm truncation.
8. Put the tail lights into the Kamm truncation.

What will this do? First and foremost, reduce the wake area from 80?x28? to 50?x16? ? a 65% reduction. This should improve coefficient of drag greatly.

I can still carry a 4x8 as well as I do today ? the classic pickup mission. I will also retain my trailer hitch.

Lose the ?elephant ears? side view mirrors in favor of CCTV and interior-mounted mirrors.

I will have immediate but secure access to the bed.

What will it look like? Google up ?Cobra Daytona coupe.? Look at the picture of the 1964 Cobra Daytona coupe and imagine the tail end of it grafted onto a pickup truck. The Daytona coupe was a very low-drag design that allowed 289 cobras to beat Ferraris down the Mulsanne straight at LeMans.

Throw in an improved air dam, side skirts, wheel skirts, and grille blocking and this may be the lowest coefficient of drag on any pickup truck.

My air dam survived a 3-5" snowfall yesterday, but that is about its limit.

wow! thats' really quite good gas mileage! Especially for a 1 ton Ford!

Big Dave, what's the approx. weight of the air dam?

It weighs about 30 pounds.

Big Dave! You mention the "slam" for your truck. Did that impact your milage and if so by how much?

Dennis

My air dam outperformed my belly pan ('94 Geo Metro) so far.

I wonder if you really need to go that low to the ground since air at the road surface should not impact the drag on the vehicle. Numbers I heard was 2.7 inches for the clearance for a car - I would think that a truck with more ground clearance could tolerate an even higher air dam since the underbody is so high up anyway. You may be adding more drag by blocking too much of the air with one that big and close to the ground.

In response to JanGeo, I have come to the conclusion that about 1.5 inch clearance above grade is about right for my truck.

First of all, that?s where road rubbing in low-speed situations ends. Mostly mine rubbed the ground under braking until it wore the dam to a 1.5 inch clearance.

Second, aerodynamic studies I?ve seen on pickups suggests that the lower clearance the better. There will be a boundary layer starting at the road surface and slowly getting thicker along the length of the truck. Pickups are long and they give that boundary layer a chance to contact the bottom of the truck. For short-wheelbase/length vehicles, maybe a 2-4 inch clearance may be A-OK.

Third, I need access to some parts of the underneath area to service the truck and that rather precludes belly pans. I may be able to incorporate a belly pan aft of the rear axle and that?s where I would fear a boundary layer building up enough to contact the truck.

It occurs to me that the reason that this airdam appears to be successful is that it is right at the front of the vehicle, it's not too far back under the bumper. This allows some of the air to escape up over the hood as opposed to only around the sides. When an airdam is too far back under the bumper, air cannot go backwards against the direction of travel to escape over the hood, it either goes out the sides, or the pressure is great enough to force it under the car anyway. If the location of the airdam further forward is problematic, a lip at the base of the airdam may stop air forcing under the bottom, and encourage to escape over the top. A lip may also enhance efficiency of an optimally located airdam.