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Old 08-30-2018, 09:49 AM   #1 (permalink)
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Deep Blue- Suburban Streamlining

All,

I have a build thread on the Central Subforum, but I wanted to make a thread in the Aerodynamics Subforum to focus more on the design than the build. I have a 1994 K2500 GMC Suburban, nicknamed Deep Blue, which has been heavily modified. I am getting to the point where I am going to start some more major aerodynamic modifications. Attached is a picture of the patient as she sits. MPG is sitting at around 23, goal is to be over 30.

Current Aero Mods-
*Roof Rack Delete
*Flush Bumper Swap
*Conveyor Belt Air Dam- V1.0

My next big project is I want to make kamm back attachments to add to the rear windows of the barn doors of the Suburban. I would love to chop the top and do a full boat tail, but I donít have time for that much body work right now and I want to keep the project marching forward. I have considered a folding/nesting design but I believe that is beyond the scope of this Version 1.0 design.

Attached is a theoretical shot of what I am imagining right now, basically the kamm would extend to the rear bumper so the overall vehicle doesnít get any longer. I was thinking on the sides of tapering at a 4:1 aspect ratio AST top view template, which I am sure I have saved around here somewhere. I will remove the roof mounted third brake light and install a light into the kamm shell. I am considering construction out of extrudedpolystyrene (XPS) foam covered in fiberglass, similar to how I made the bedcover for my Tacoma.

Thoughts?

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Old 08-30-2018, 10:44 AM   #2 (permalink)
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I think that will be a great start! Why not a couple inches further and maybe bring the sides down toward the rear bumper? Maybe a flush rear bumper so no air can get inside the bumper and act as a parachute?
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Old 08-30-2018, 11:35 AM   #3 (permalink)
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The halves of the Kamm-back swing with the doors? That angled cutline suggests it.
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Old 08-30-2018, 11:38 AM   #4 (permalink)
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30-mpg

For Deep Blue to get 30-mpg on the highway,you'd need to drop the Cd to around 0.168.
You'd be looking at the GM Precept concept car,circa 1999.
That would require everything I did for the Spirit of Ecomodder,and no less than 8-feet of boat tail,unless you could get rid of your mirrors completely.
A new Colorado/Canyon Diesel will get the mpg,but your looking at around $40,000.00?,and expect to drive 62-mph.
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Old 08-30-2018, 03:32 PM   #5 (permalink)
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19BoneStock88,
Thanks, the reason I stopped it higher was to not block the tail lights. I want to swap out the bumper to a custom design, preferably integrating with a diffuser from the belly pan.

FreeBeard,
Yes, the plan was to directly attach the kamm-back in two pieces to the barn doors, probably with a few fasteners and high strength tape. Because the hinge is at the outside door face, near the top it can be out near the side edges but not bind upon opening. I figure this is the simplest way to build it, as any other method I have thought of will require separate hinges/lifting to allow the doors to open.

Aerohead,
Well, that doesnít sound promising then, at least not until I can do the full chop-top. I was hoping the MPG would be achievable at a more achievable figure, as I figure I am at 0.45 right now. I may should have mentioned I am expecting some of the increase to get to 30 to come from gearing changes (discussed in my build thread) not solely from aerodynamic mods. I need to get basically 30% better MPG than right now to break 30 MPG.
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Old 08-30-2018, 05:35 PM   #6 (permalink)
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gearing

Quote:
Originally Posted by aardvarcus View Post
19BoneStock88,
Thanks, the reason I stopped it higher was to not block the tail lights. I want to swap out the bumper to a custom design, preferably integrating with a diffuser from the belly pan.

FreeBeard,
Yes, the plan was to directly attach the kamm-back in two pieces to the barn doors, probably with a few fasteners and high strength tape. Because the hinge is at the outside door face, near the top it can be out near the side edges but not bind upon opening. I figure this is the simplest way to build it, as any other method I have thought of will require separate hinges/lifting to allow the doors to open.

Aerohead,
Well, that doesnít sound promising then, at least not until I can do the full chop-top. I was hoping the MPG would be achievable at a more achievable figure, as I figure I am at 0.45 right now. I may should have mentioned I am expecting some of the increase to get to 30 to come from gearing changes (discussed in my build thread) not solely from aerodynamic mods. I need to get basically 30% better MPG than right now to break 30 MPG.
According to Gino Sovran (he's kinda the God of GM's research arm),you'd do all your aero and tires and whatever else,then fit the gearing to maintain the same BSFC for your engine.If not,you could lose a significant portion of your mpg potential.If you have Hucho's book he goes into this.
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Old 08-30-2018, 10:00 PM   #7 (permalink)
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There's Hucho, then there's funkhoss:

https://ecomodder.com/forum/showthre...mpg-33961.html
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Old 09-04-2018, 04:05 PM   #8 (permalink)
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Aerohead,
I agree with the concept of gearing changes as aero improves(and I have read most of Huchoís book) the problem being I am turning more RPMs than necessary as is, with some of those potential gearing gains already on the table. I have found a several BSFC charts in open literature for the 6.2/6.5 diesels which lead me to believe being moderately loaded (e.g. 50-100%) at low RPMs (e.g. 1200 to 1800) is ideal for this engine.

Freebeard,
Thanks for the link, I know funkhoss had referenced his project in my other thread, but I didnít read his build thread until now.

Everyone,
Didnít get much time to work, but I did manage to get a good picture for an overlay plus did some measuring/figuring. The taper at the rear of the roof is meh, very shallow then quickly very steep, so it will be of little use. Also the angle at which the Suburban sits cancels out some of this taper. Attached is my overlay.
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Old 09-04-2018, 10:01 PM   #9 (permalink)
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Had a neighbor regularly got 27-mpg with his 6.2 4WD Suburban. His father a GM exec, and son no dummy. Quizzed him on it. A friend got same with first year 6.2 pickup. Both automatics c

My 4T 2WD Cummins will also see 27-mpg. Stock. 58/9-Mph. On cruise control.

All of these in south central US. LSD, not ULSD.

I see mpg gains with both Power Service and Howes Meaner Cleaner. Not big, but adds to margin.
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Old 09-05-2018, 05:51 AM   #10 (permalink)
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Quote:
I would love to chop the top and do a full boat tail, but I don’t have time for that much body work right now and I want to keep the project marching forward.
Quote:
The taper at the rear of the roof is meh, very shallow then quickly very steep, so it will be of little use. Also the angle at which the Suburban sits cancels out some of this taper. Attached is my overlay.


Golf GTI W12-650. The best treatment I've seen for a box shape. Chopping the top loses interior volume too, but it's more work. What you have are three external ducts that feed the wake with high-speed jets of air. Another example the Citroen Tubik:


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