Hope For Lifted 4x4s - PowerStrokeNation : Ford Powerstroke Diesel Forum
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post #1 of 25 (permalink) Old 01-20-2008, 03:36 AM Thread Starter
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Hope For Lifted 4x4s

I had the bad bod today, so I got caught up or my reading.

I read a postgraduate dissertation on aerodynamics of pickups. To make a long (185 pages) short he put an air dam similar to mine and a fairing similar to mine and he improved his MPG by 20%.

All this on a 4x4 slightly lifted Dodge Cummins with an automatic. He made no effort to do anything beyond those two mods.

If he can do it you can do it better.

2000 F-350 SC 4x2 6 speed
3.08 gears Gear Vendor Overdrive
Slammed 4"
Rugged Air Dam
315,000 miles
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post #2 of 25 (permalink) Old 01-20-2008, 05:23 AM
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Re: Hope For Lifted 4x4s

I have been thinking about that. I am building a custom bumper for the front of my truck and I was going to include provisions in it to put some sort of flaring or valance on the front of it.

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post #3 of 25 (permalink) Old 01-20-2008, 07:47 AM
 
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Re: Hope For Lifted 4x4s

Good news Dave! I'm gonna lift mine 3.5" and I was dreading the mileage drop. I think I'll think of a decent looking way to do an air dam.
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post #4 of 25 (permalink) Old 01-21-2008, 07:22 AM
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Re: Hope For Lifted 4x4s

Don't you ever have any issues with it catching on stuff? Also what's the best material to make one out of?

Not to derail but do you think it would make a diffrence if I screwed down a piece of plywood over the back behind the toolbox & ran it to the tailgate?


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post #5 of 25 (permalink) Old 01-21-2008, 12:25 PM
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Re: Hope For Lifted 4x4s

i dont think a piece of plywood would do anything, according to mythbusters on a pick up when the air comes over the cab it goes into the bed creating a circulating motion. so while air is cirulating in your bed the other air glides over top of it.

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post #6 of 25 (permalink) Old 01-21-2008, 01:54 PM
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Re: Hope For Lifted 4x4s

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Originally Posted by Cat_Rebel View Post
Don't you ever have any issues with it catching on stuff? Also what's the best material to make one out of?

Not to derail but do you think it would make a diffrence if I screwed down a piece of plywood over the back behind the toolbox & ran it to the tailgate?
you will need 2 pieces, because the bed is slightly larger than one. i cut boith pieces on an angle, ran 3 strips (one in the front, middle, and back) of wood to hold it together, also letting those strips over extend the plywood by about 2", and dropped it in. the plywood sat flush with the bed, and the strips held everything up since they were on the bed rails.

did it give me better mileage? deffinately. i need to make a new one now for my stacks though

2005 F350 prairie tan/black crew cab FX4 innovative tunes, exhaust

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post #7 of 25 (permalink) Old 01-21-2008, 02:37 PM
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Re: Hope For Lifted 4x4s

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Originally Posted by Powerstrokin444 View Post
i dont think a piece of plywood would do anything, according to mythbusters on a pick up when the air comes over the cab it goes into the bed creating a circulating motion. so while air is cirulating in your bed the other air glides over top of it.
But, that circulating air is turbulence. The air that is circulating has separated from the rest of the air coming over the top & sides of the cab. If you can keep the air from separating, then you gain quite a bit of efficiency. What myth busters saw (IIRC), is that by keeping the turbulence in the bed made it into a consistent turbulence. Lowering the tailgate makes the turbulence unstable. That is why Dave's bed cover slopes down to the top of the bed. He is keeping the air from separating. No separation = no turbulence = less power demand = better fuel economy.
Same principle with the air dam, except underneath.

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post #8 of 25 (permalink) Old 01-21-2008, 03:58 PM
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Re: Hope For Lifted 4x4s

Where could I buy some of the Airdam material like conveyor belts?

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post #9 of 25 (permalink) Old 01-21-2008, 04:56 PM Thread Starter
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Re: Hope For Lifted 4x4s

My material is 3/4 inch by 24" conveyor belt. I got it at a local industrial rubber supply house. The stuff is not cheap and it is a bear to work with. It has a lot of steel "angel hair" in it like a tire. I cut mine with a Sawzall with a hacksaw blade and drilled it with a wood bit, but the wood bit was shot after nine holes. The upside is that this stuff is completely invulnerable to the dead dogs you hit on the road. Mine is held on by nine nutserts and capscrews with fender washers. It goes on (after the holes are cut) and comes off in five minutes with a ratchet and socket.

Some advice from experience.
When fitting up the air dam put a couple of one bys under it. I used one and had it initially 3/4 inch above grade. It rubbed on the ground when I hit the brakes and the truck nose-dived in reaction. After a while it stopped rubbing at about 1.5 inch clearance. The closer the better, but it will rub on real world roads if you don't give it some clearance. I called it "letting the road mark the air dam."

When fitting up the air dam, start in the center and put 4-6 washers between the air dam. One the holes beside the center one reduce the washer count by one. At the next hole reduce again. Finally you reach zero. The idea here is to impart somewhat of a "bow" or "cowcatcher" to the air dam so it will tend to bat the air to the side rather than drive it along like a bulldozer blade. As a result of my flat air dam the center of the thing vibrated like a clarinet reed and haggled up the holes.

After the air dam is fitted up, make a papaer pattern of your holes and cut a piece of metal (I'm thinking 12 ga stainless) about 4 inches wide to act as an improved "washer" and spread the clamping load out along the whole upper part of the air dam. Fender washers don't really spread the load enough and when the dam got to working, the fender washer edges started cutting into the rubber, weakening the air dam.

The air dam never seems to catch on anything, but if you have a yen to go off road I'd recommend stopping and spending five minutes getting it off. Mine tolerates 3 inches of snow but 5 inches defeats it. That's why it is rolled up in the garage until the snow quits.

It never fouled the front tires but if you want to drive the truck up some ramps for service, you may need to take it off to do so.

I suppose you could paint this stuff but I don't know how well it would stick.

Paradoxically, the air dam helps with engine cooling. All that air that normally goes under the truck is cut off and a vacuum forms under the truck. The vacuum aided by the higher pressure at the grille will jam more air through you radiator/intercooler/AC condensor.

2000 F-350 SC 4x2 6 speed
3.08 gears Gear Vendor Overdrive
Slammed 4"
Rugged Air Dam
315,000 miles
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post #10 of 25 (permalink) Old 01-21-2008, 05:05 PM
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Re: Hope For Lifted 4x4s

great info, but i am curious as to how well it would work with our lifted trucks. i mean i comletely understand the concept, but lets say this air dam is 36 inches tall, wouldnt it collapse at say 60 mph? or would it be possible to say have the dam go from the bumper to the front axle to help divert air?

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