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Old 04-27-2017, 10:09 AM   #11 (permalink)
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Since I was reasonably certain that the rear "shell" was an ok idea but really, REALLY poorly executed, I did the only rational thing. I hacked most of it off! I probably cut way too much off initially, and went from no taper (or outwards flare) to too much taper. It's pretty easy to build it a little higher with foam, but it's a serious PITA to hack up fiberglass sheet and reshape it. Here's the first test, you can see a somewhat reasonable taper top to bottom.



Unfortunately the zero-taper-top and the heavily tapered sides caused some serious vortex action near the top of the sides:


My MPG stayed steady at ~13.7 with this taper, even with the horrible vortex. I had a spare backup camera so I installed it on an aluminum arm so I could see how bad it was.

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Old 04-27-2017, 10:11 AM   #12 (permalink)
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I was fairly certain that the zero-taper-top was a big part of my screwup (when all else fails, FOLLOW THE TEMPLATE!) so I cut that off completely, and left the sides as is. MPG immediately jumped up from 13.7 to 14.4 and it was noticeably easier to cruise on the highway.



I moved the 3rd brake light to below the windows, so I can do a variety of experiments and not have to remount the lights all the time. It's legal, since they only need to be roughly centered and above the height of the left and right tail lights. As expected, the tuft testing on the side looked great, with no inversion, no separation, and very little visible turbulence. It may not be the optimal departure angle (especially near the top), but the tuft testing showed that it was at least not a disaster zone!!!

I added back in the center section, this time with a slight taper to it, about 3 inches down over 20 inches run. That's about an 8-10 degree departure angle. The corners are still wrong, but my MPG stayed consistent at 14.3-14.4 for 2 tanks. This isn't really an improvement over no center section, but it's a lot better than with the old moronic one! It's also pretty nice looking on the tufts. However, I'm looking for improvements, so I made myself a wooden taper gauge. I'm currently experimenting with a 12 degree departure angle and a 1.5 degree per inch taper rate. This is steeper than The Template, but it matches what Mercedes and Ford have done with the Sprinter and Transit vans. They both have fairly flat sides, and then go to a 10-12 degree taper at the back end. Ford uses a pretty sharp kink to get to that angle, and Mercedes uses a smooth curve. Here's my partially-carved build of foam to get there, you can see my taper gauge on the left:
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Old 04-27-2017, 11:39 AM   #13 (permalink)
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Wow you have done a lot of work already.

I trust most of it was fun.

I missed what you have done for a front chin spoiler.

What sort of suggestions are you looking for at this point?

In the early 1980's I had a short-box E-100, the only thing aero-wise I did was the front chin spoiler. It didn't raise the mpg (from what I could tell), but made it much safer to drive on the highway, especially on windy days.

Do you have electric cooling fan(s) and a grill block?

If you have high miles the fan clutch might be going, replacing it with electric fan and controller makes the engine run smoother. All that added fan mass and clutch silicone over the water pump is not needed.

I am not a fan of grill blocks, I've had one fan controller already fail on me, ram air was the only way I got home. However it is supposed to make a difference.
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http://ecomodder.com/forum/showthrea...1-a-19525.html

Last edited by kach22i; 04-27-2017 at 11:51 AM..
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Old 04-27-2017, 12:02 PM   #14 (permalink)
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Most of it was pretty interesting, though not all of it was effective! I haven't done a chin spoiler yet, but am planning on doing that after I finish the passenger side skirts.

At the moment I'm working on the rear taper, and my results have been mostly inconclusive:

1) I know the non-tapered rear shell was not an improvement in FE or handling.
2) The initial cut taper on the sides made no significant change (20-30 degree taper).
3) Removing the non-tapered top entirely made a significant improvement (+5% FE).
4) Installing a somewhat tapered top made no difference vs no top.
5) Changing the side taper from 20-30deg to ~12deg seems to be a -5% FE.

I'm not sure on #5, since I fixed the A/C last week and used it a lot. So I'm running again this week with A/C and then probably next week without A/C to confirm. Basically I'm looking to get the rear taper "correct" before moving on to other areas like side skirts, bellypan, front spoiler, rear wheel covers, front tire air curtains, etc.
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Old 04-27-2017, 06:06 PM   #15 (permalink)
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belly pan for sure. I would consider a partial grill block with some ducting the remaining air directly to the radiator, I agree with kach22i, you don't want to put yourself in danger of ruining your engine. I did this to a lesser degree on my Saturn ion (towed 3500lbs without overheating) and plan on doing this to a larger degree on my gmc acadia.

you might want to make standoffs for the belly pan so you can keep it flatter and cover more of the bottom, this would make a huge difference in stability, noise, and most likely in economy. splitters/front mount air dams (see chevy volt and traverse for OEM examples that work well) will compliment this for sure.

getting the taper just right is a challenge



maybe you can pull angles from this sample diagram? I know for any angle, your rear tapers are awful short, and need to be longer likely for any noticeable effect.

AeroTech Caps | Aerodynamic Wheel Covers, Trailer Skirts and More!



these are some production EPA certified examples for inspiration
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Old 04-28-2017, 05:00 AM   #16 (permalink)
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Quote:
Originally Posted by Isoldmysaturn:( View Post
.......maybe you can pull angles from this sample diagram? I know for any angle, your rear tapers are awful short, and need to be longer likely for any noticeable effect.
Excellent observation, and those diagrams you posted clearly illustrate the affect length makes.
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Architect, Artist and Designer of Objects

1977 Porsche 911s Targa
1998 Chevy S-10 Pick-Up truck
1989 Scat II HP Hovercraft

Chin Spoiler:
http://forums.pelicanparts.com/off-t...effective.html

Rear Spoiler Pick Up Truck
http://forums.pelicanparts.com/off-t...xperiment.html

Roof Wing
http://ecomodder.com/forum/showthrea...1-a-19525.html
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Old 04-29-2017, 06:22 AM   #17 (permalink)
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Quote:
Originally Posted by Merlyn2220 View Post
I'm currently experimenting with a 12 degree departure angle and a 1.5 degree per inch taper rate. This is steeper than The Template, but it matches what Mercedes and Ford have done with the Sprinter and Transit vans. They both have fairly flat sides, and then go to a 10-12 degree taper at the back end. Ford uses a pretty sharp kink to get to that angle, and Mercedes uses a smooth curve.
Euro vans are designed aiming an ease to load them with a forklift in mind more than aerodynamics. Anyway, have you never considered to do some more extensive mods to the rear end in order to keep the tail lights more visible from the sides in a way similar to stock and eventually fit some custom-made rear doors that would fill the gap between the roof extension and the bumpers for a "cleaner" look?
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Old 05-01-2017, 10:50 AM   #18 (permalink)
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One of my "thought projects" has been to extend the bumper about a foot back. This would let me encapsulate the hitch and provide a longer diffuser for the belly pan. Practically speaking, this might not be easy as the deeper bumper has to be strong enough to stand on for loading/unloading. But if the rear taper (6-10" total) isn't big enough to make a significant improvement in FE, then a 12" extension on the bumper probably isn't going to improve things enough to matter either.

For taillights, I have side marker LEDs that I will install once I have the taper figured out. I'll just follow the DOT rules for lighting with turn signals. Cars like the Corvette have no taillight visibility beyond 90 degrees, and they are legal with the side marker light.

Regarding the grill block and fan, I have avoided doing anything with that until I have a reliable temperature gauge readout. Since it's OBD-1, all I currently have is a dumb sweep gauge that goes all over the place depending on whether the AC is on, if it's at idle, coasting, etc. I have a plan to add a "real" gauge with digital readout, I just haven't built it yet. It'll happen soon, as I want to get temp readings in the summer to be sure I'm capturing worst case under load.

I have an electric fan set up that's ready to install. I might actually go over to my local dyno and run a with/without stock fan test, just for fun.
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Old 05-01-2017, 01:30 PM   #19 (permalink)
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Quote:
Originally Posted by Isoldmysaturn:( View Post
you might want to make standoffs for the belly pan so you can keep it flatter and cover more of the bottom, this would make a huge difference in stability, noise, and most likely in economy. splitters/front mount air dams (see chevy volt and traverse for OEM examples that work well) will compliment this for sure.
I made standoff brackets for the driver's side bellypan, though I need to readjust the height on 1 point so it holds the pan flat. I recall reading somewhere that you really need to start the pan from the front nose back, which might be why my existing 1/4 pan seems to have a negative effect on FE. The air under the nose and engine is utter chaos, and there's only the factory 2" front lip under the bumper. I can intuitively see how having an axle-to-axle bellypan under only the driver's side could make the drag worse than without anything at all. It would create a high pressure area in the front, and low pressure behind it, as the pan forces air to the passenger side and then sucks it back to the driver's side as it tries to exit the back. This might be one of those "all or nothing" mods, instead of trying to do it piecemeal like I've been doing on everything else.

That reminds me, when I was building the driver's side skirts my worst (almost ever) tank of gas was when I had the front wheel done, but hadn't yet built from the driver's door back. It looked a lot like a DTM car, but without the airflow vented out of the engine compartment. The drag was noticeably worse on the highway, and drastically improved when I added on the rest of the skirt. I can see how the partial piece of bellypan could do the same thing.

I'll have to check out the Traverse, it's not one that I've looked at. There's a Volt here at work, so I get a chance to look at it in detail every once in a while.
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Old 05-01-2017, 01:50 PM   #20 (permalink)
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BZP T-100 (2010) - '98 Toyota T-100 ext cab - 3.4L/auto SR5
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BZP T-100 (2011) - '98 Toyota T-100 ext cab - 3.4L/auto SR5
Last 3: 23.66 mpg (US)

BZP T-100 (2009) - '98 Toyota T-100 ext cab - 3.4L/auto SR5
Last 3: 19.01 mpg (US)

BZP T-100 (2012) - '98 Toyota T-100 ext cab - 3.4L/auto SR5
90 day: 19.68 mpg (US)

BZP T-100 (2013) - '98 Toyota T-100 SR5
90 day: 20.6 mpg (US)

BZP T-100 (2014) - '98 Toyota T-100 SR5
90 day: 21.28 mpg (US)

BZP T-100 (2015) - '98 Toyota T-100 SR5
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BZP T-100 (2016) - '98 Toyota T-100 SR5
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BZP T-100 current (2017) - '98 Toyota T-100 SR5
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Take a peek at my belly pan thread.
T-100 belly pan...

Current view from the front.

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