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Old 06-22-2007, 11:04 AM   #1
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To all the aero geniuses/creative inventors....

I'm not sure if you've noticed, but the 89 Jeep that I'm driving has all the aerodynamics of a farm tractor in reverse. This is killing my attempts at good MPG, or coasting in general.

Earlier today I managed to obtain some thin coroplast from a local sign shop. I've got 5-6 sheets of this stuff, roughly 6ft x 18in. I'm wondering what to do with this good stuff now.....(and what's a good way to connect these sections together?? Duct-tape and glue on the back side??)

I was thinking of belly pan...at least from factory air-dam down to front axle. I'll have to be somewhat creative on this one...that's not really my strong side

I was also thinking of grille-blocking and such. The only downside I can see is that the spotlights I've got mounted to the bumper would negate any benefit from grille-blocking (plus the constant worry of overheating, etc....)

We're trying to get the most bang-for-the-buck here....I'll have some time this weekend to play around, so we'll see what happens.




PS - This coroplast will stand up to water/spray from the road, as well as oil drips/etc from the block, correct?? I'd rather not build this belly pan, only to have it disintegrate or melt/catch fire on me.....



*edit* Some photos of the front end of the Jeep are in my garage. Now if I could only figure out how to insert photos into this thread......
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Old 06-22-2007, 11:26 AM   #2
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Ya, coroplast can stand water and oil. Not sure how much heat it can take.

Yesterday I harvested a 4x8 foot piece of it that had grown beside the road on my way home. The final run-off election was last weekend so I figured that it was technically garbage, at best... When I had been driving by, it looked like a 3x6 piece, so when I finally cut it loose and got it to the back hatch of the Element it was a bit of a scramble getting it stuffed in there. :-)

I am going to use it to make a belly pan. I will use gorilla glue to stick flashing on the inside of any part that seems like it might get hot. I'm leaving the first several feet of the exhaust unenclosed, but will be covering the muffler in the rear.
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Old 06-22-2007, 11:28 AM   #3
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The last time I had an IQ test, I was far below "genius"....and my creativity level is sporatic at best. But to get to the bottom line....

Quote:
Originally Posted by Raccoonjoe View Post
I'm not sure if you've noticed, but the 89 Jeep that I'm driving has all the aerodynamics of a farm tractor in reverse.

We're trying to get the most bang-for-the-buck here....
IMO, Lower it...plain & simple. It probably isn't the least expensive option and there are individual practicality concerns that go along with it. But on a vehicle like a Cherokee, all of the coroplast in the world won't lower the cd as much as a 1"-2" drop will. Someone please correct me if I'm wrong.
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Old 06-22-2007, 12:01 PM   #4
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Quote:
Originally Posted by SL8Brick View Post
IMO, Lower it...plain & simple. It probably isn't the least expensive option and there are practicality considerations that go along with it. But on a vehicle like a Cherokee, all of the coroplast in the world won't lower the cd as much as a 1"-2" drop will. Someone please correct me if I'm wrong.
I appreciate the input there, but here in Indiana, we can get some pretty nasty snow/floods....and I bought a Jeep so I could *use* the 4WD. This involves ground clearance.....So it looks like lowering the Jeep is out of the picture for now. (Plus a drop would probably mean new tires and many other expenses....Just not sure it would ever pay for itself. I also like the fact that I can change my oil without jacks, ramps, or parking lot curbs)

The coroplast is going to be a "permanent temporary solution"....i.e. It will be there 90% of the time, but will also be removable for those times that it needs to come off.....
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Old 06-22-2007, 12:10 PM   #5
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Understood, Racoonjoe. Like I said..."practicality considerations/concerns". But I wish you all the luck in the world w/the coroplast install. I'm sure that the other experienced folks here will steer you right.
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Old 06-22-2007, 01:10 PM   #6
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Coroplast sheeting on the bottom sounds good to me.
Think about a Kamm back or boattail. For pics of a partial Kamm back see
http://www.gassavers.org/garage/view/272
Why the back? One study showed the rear as the single worst contributor of drag for vehicles. Worse than the front or the bottom.

Kamm concept: You can look it up in wikipedia or search here. An ideal automotive rear is a tapered shape like the trailing end of a falling droplet. Like an airplane wing's rear; gradually gets smaller. If you cut off the back portion of the taper you still get much of the benefit of the full taper. Many hatchbacks use the basic Kamm design. You could build it in coroplast - but you might need a full sheet as opposed to strips.

I'm about to do a similar treatment on the back of my wagon (like the Geo in above link). Just like on the Jeep, the big squarish flat back is a killer (BAD) for aerodynamics.
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Currently getting +/- 50 mpg in fall weather. EPA is 31/39 so not too shabby. WAI, fuel cutoff switch, full belly pan, smooth wheel covers.

Now driving '97 Civic HX; tires ~ 50 psi. '89 Volvo 240 = semi-retired.
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Old 06-23-2007, 02:35 AM   #7
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Re. belly pan work on the Jeep - if you build it out of steel or aluminum then there's a macho effect. People who aren't aware of FE concerns will assume it was built for protection. Of course that's more expensive and probably more time consuming than building it in coroplast.
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Currently getting +/- 50 mpg in fall weather. EPA is 31/39 so not too shabby. WAI, fuel cutoff switch, full belly pan, smooth wheel covers.

Now driving '97 Civic HX; tires ~ 50 psi. '89 Volvo 240 = semi-retired.
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Old 06-24-2007, 09:56 AM   #8
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Quote:
Originally Posted by SL8Brick View Post
The last time I had an IQ test, I was far below "genius"....and my creativity level is sporatic at best. But to get to the bottom line....

IMO, Lower it...plain & simple. It probably isn't the least expensive option and there are individual practicality concerns that go along with it. But on a vehicle like a Cherokee, all of the coroplast in the world won't lower the cd as much as a 1"-2" drop will. Someone please correct me if I'm wrong.
Well, since I am indeed certified. No, wait he wanted a genius, my certification is from the psychiatric clinic.

Lower it, add an air dam, add side skirts. Ditch the luggage rack (if you haven't already), make a grill insert, depending on the engine, get rid of the mechanical fan. Got them big tires? Save them for the winter, use skinnier tires. See that rear bumper sticking out? Smooth that deal out. Think about fender flairs to direct the air around the wheels and tires. That 4wd will kill you too.

My kid's got one in case you haven't guessed and I'm attempting to help him get better mileage, but as always he knows so much more than I do it's a wonder the planet lasted as long as it has without his guidance all these millions of years.
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Old 06-24-2007, 10:21 AM   #9
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Could do a belly up while you are down there.
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Old 06-24-2007, 12:02 PM   #10
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My kid's got one in case you haven't guessed and I'm attempting to help him get better mileage, but as always he knows so much more than I do it's a wonder the planet lasted as long as it has without his guidance all these millions of years.
Mark Twain said (approximately accurate quote), "When I was seventeen I was amazed at how stupid my father was. When I was twenty-one I was amazed at how much he'd learned in those few short years."

The trick is to help keep 'em alive till they get to that latter stage.
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Currently getting +/- 50 mpg in fall weather. EPA is 31/39 so not too shabby. WAI, fuel cutoff switch, full belly pan, smooth wheel covers.

Now driving '97 Civic HX; tires ~ 50 psi. '89 Volvo 240 = semi-retired.
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