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Old 12-02-2017, 04:43 AM   #1 (permalink)
gumby79
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Location: Butte, Montana
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little jona - '91 Dodge D 250 first gen cummins LE
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Last 3: 24.65 mpg (US)

Little Jona airo modded - '91 Dodge RAM 3/4 TON D 250 24 AUTO
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Full size pick up air dam . Quick and dirty prototyping. With aba cost down test

Well my stack of bricks is , , a stack of bricks .
Before

17" under the bumper and 12" under the cross member.
So i added an air dam of 2.5", from a 90's full size Ford Bronco . This was 3" short . So I simply cut it in hafe, spread the parts and bolted it through stock and drilled holes in the bottom of the bumper. To cover the missing pice I moved the licence plate to the lower holes . This was going to work out . Liked what I saw except the suspension and cros mimber hang down below my new addition.


So down to the hardware store to get some longer bolts( 6-3") and some nylocks and washers. Had to run a tap up the sholder
To the head($0.35 ea Vs$1.65 for pre threded) for a full thred to be able to clamp at both ends of the bolt (1 nut securing the bolt to the bottom of the bumper and 3 nuts holding the air dam) and delete the need for a spacer/shim.
So I set this with the center 5" (2.5"+the 2.5" of the doner part)to the bottom of the lowered licence plate . For 2 reasons 1 I was lazy and didn't want to make a filler to support the center (were I spred width) 2 this made it to were the only part hanging down below the air dam in the middle was the oil drain plug. On the corners I set the air dam down to 7"( 4.5" bolt+2.5"). This angled profile came to the bottom of the lower control arms.


Now I was planning this out as I went . I had som 1/8" paneling that I was going to make a flushed out filler going from the crome to the now lowered air dam. Cover the panel with paint and it would survive for an extended period of time. But then concitered that I wanted to runn the air dam at several different hights, this would require a sophisticated curved structure to be built for each version. And decided to test the durability of a quick prototype material. Self adhesive shrink wrap tape 6" wide.
Quote:

6″ Heat Shrink Tape (DS-706)
6" wide by 180' long heat shrink tape. 9mil-backed tape with no UV inhibitors. Heat shrink tape is designed to tape seams, patch holes and secure zipper access doors. Available in white, blue and clear.

*IMPORTANT* Clear tape is NOT recommended for usage longer than 60 days. An adhesive residue will result. Clear tape is not recommended for outdoor storage
$41.40usd
I installed the tape even with the bottom of the Ford part. And set the remander as high up the bumper as I could wile maintaining a wrinkle free application ( using heat from an iorn for skin skinning a modle airplane($5 pawn shop) strategically to shrink pleets that apply flat on a curve) .
Apply heat with verious methods . Propain torch, 1500w heat gun, the skinning iron. It helps to practice on sone to learn your technique. But I said quick and dirty right. So out with the tools . Start with kiss, No cords let there be light of fire. The pencle tip style torch head concentrated too much heat too small. Eather to fast to activate the shrinkage or to hot and melt, drat. My goldy lox wasn't happy so I try the other tip with a spred 3 fingerd flame a little better . This stuff is thinner than what I used on my Aero Tonto. and that makes it more finicky. It will shrink just with fire, just more time required to reach an acquit levle of mastery than I want to invest at this time. Next the modle skinning tool.

However now that I find a pic of one it shows a sock /slipper pad that would have helped (I'll have to try that) this tool did get hot enough, however the plastic would get slightly tacky and strech funcky. Agen more time /skill /knolage needed.
On to the tryed and true hot air gun. The one I have is a digital-+5f settable. I started at about 250f and worked my way up to were the plastic was behaving it self, pulling tight not pulling too tight and creating a hole. . This worked.

As you can see the arbitrary drop was just right.
Off to the mountains to test with the go pro and make shure it is stable at speed . A warm up route takes me through 25 , 35, 45, 55, 80mph zones and 15-20 mi to the top of a grade. Were I gravity drop from 65mph down a 6% 3mi grade. Lost a small amount of speed 80mph vs 85mph w/o. 3 runs down ea.( only bolts hanging for A2 test) . Back to the house and try V2 .
V2
Same as the first but diffrent.
This time I wanted to see if It (with the life I live)could handle going lower?. Skip forward no I can't except this. To extend the air dam down I simply added long(2" cupler) nuts with a nylock jam nut ,to the bolts alredy installed. And some 3/4" long bolts from the bottom. This time the tape is not wide enough, 1.5" short. So 1 layer/1/2" on the lower plastic and up to about(+-1/2") the same place on the bumper. Shrink this. 2nd layr is alined with the bottom of the black plastic and shrank. Quick and dirty.

Some notes on layering.... air bubbles are horable avoid them.
As you heat to shrink the air expands streching/growing till you stop Appling heat. Then the shrink wrap cools faster than tbe air harding as a lump. ****ion was to work the bubbles to an edge to get them out . Some were bonded in bad or to far from an edg so I poked the air bubbles with a needle. Wala nice and smooth. Kind of like Appling decals.

B test was unperceivable difference from V1

Low + backwoods dont go together. This is my alternative rout to 80mph Interstate it a "drover road"(means unmaintained cattle drive road). I did manage to hook the unsuported section on some rebar poking out of a parking block.
Ran this way for a wile. (Jun -Sept.) Knew it was negative mpg but you dont know what you havd your hands around till you do distructive testing I mean this is tape how strong is it ? Can it take a rock at 70mph ? 100mph+ air speed? (Don't kid your self even Ecomodders brake 100mph air speed 55mph road speed + headwinds of over 50= over 105mph ) well it sustained 70mph +50mph head wind with gusts to70mph so 140ish. hundreds of dirt road miles with a few ground strikes (in this lowest ppsition it was 2"below the drain plug) a cupple hard strikes in driveways (some of the same places my Aunt hits inher hybrid) and 3/4 of a trip to the west desert of Utah. The overgrown sage brush(wetter than average year resulting in biger than normal growth ) and a cupple ground strikes broke 3 of the 5 bolts on the passanger side hafe. It was still atached by the shrink wrap tape and 2 bolts. They sheared off from work hardening. (Haveing been bent and straightened many times.
Whis was 2 weeks before Darco. So when I got to town I re set It to my desired height 2"center and 5" on the corners. At Darco Aerohead, Freebeard, and I learned that the operator of the wind tunnel had yet to see an air dam that actualy reduced CdA. Lance has tested many prototypes that were on there way to Bonneville for Land Speed racing record attempts. S hear is the data its only a/b but it is empirical data.
Cd 0.680 with airdam and Aero Tonto (B)
Cd 0.661 with just the Aero Tonto (A)
=3% loss.
DISCLAIMER the difference between the two tests is accurate, HOWEVER the Total Cd value is skued high due to tunnel wa interference..
So in the end I am not running an air dam.

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__________________
1st gen cummins 91.5 dodge d250 ,HX35W/12
ehxsost manafulld wrap, Aero Tonto
best tank: distance 649gps mi 24.04 mpg 27.011usg
Best mpg : 29.3mpg 97mi 3.311usg 7/27/16


Former
'83 GMC S-15 Jimmy 2door 2wd O/D auto 3.73R&P
'79 Chevy K20 4X4 350ci 400hp msd custom th400 /np205. 7.5-new 14mpg modded befor modding was a thing
87' Hyundai Excel
83 ranger w/87 2.9 L FI2wd auto 18mpg on the floor
04 Mitsubishi Gallant 2.4L auto 26mpg
06 Subaru Forrester XT(WRX PACKAGE) MT AWD Turbocharged 18 plying dirty best of 26mpg@70mph
95Chevy Blazer 4x4 auto 14-18mpg
04 Chevy Blazer 4x4 auto 16-22mpg


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The Following 5 Users Say Thank You to gumby79 For This Useful Post:
aerohead (12-02-2017), Ecky (12-02-2017), oldtamiyaphile (09-26-2018), slowmover (12-14-2017), Vman455 (12-02-2017)