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Old 04-03-2018, 10:20 AM   #11 (permalink)
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Thanks for this. Good news.
I did the calcs for this for my car, and I like the results.

I get an angle of 3.69 for the diffuser's upward slope, using existing available attachment surfaces. That's assuming the panel prior to the diffuser is horizontal, which I believe it is. Pretty close, anyway. The rear bumper lip is 2" higher than the existing support I'll use to support the diffuser's leading edge (which will also support the prior panel's trailing edge). The diffuser is 31" long at the center, so that's an angle of 3.69 per a handy calculater on the web. Allowing for the bumper's curve, if the diffuser length is only 25" at the sides, the angle is still 4.57. According to the chart you posted, either case gives a reduction in Cd. Thanks!

The calculator I used

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Driving '00 Honda Insight, acquired Feb 2016. On hold: plans to purchase an Elio enclosed reverse trike, due out some time in 2018.

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Old 04-03-2018, 10:31 AM   #12 (permalink)
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I did some other measurements today, on the exhaust system's low points. They are 2" below the existing lip where I will attach the center panels' outer edges. Based on where I can place lengthwise runners to "press" the panels lower - to clear the exhaust low points - that gives an angle of 4.86 at those added bend points. But I'd need to extend lower than that to have true clearance below the low points, for protection against heat and vibration.

So an additional 3/4" of clearance below the low points, would create lengthwise bends in the panels of 6.67. I might rather keep the panels relatively flat, and make a couple cutouts for the exhaust protrusions.

Last edited by brucepick; 04-03-2018 at 02:37 PM..
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Old 04-03-2018, 01:15 PM   #13 (permalink)
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Quote:
Originally Posted by brucepick View Post
...create lengthwise bends in the panels of 6.67. I might rather keep the panels relatively flat, and make a couple cutouts for the exhaust protrusions.
This is a poblem that discouraged me too. (And my desire not to drill the body.) Nonetheless, a 6.67 angle is better than a 90 degree angle any day, no?
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See my car's mod & maintenance thread and my electric bicycle's thread for ongoing projects. I will rebuild Black and Green over decades as parts die, until it becomes a different car of roughly the same shape and color. My minimum fuel economy goal is 55 mpg while averaging posted speed limits. I generally top 60 mpg. See also my Honda manual transmission specs thread.

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Old 04-03-2018, 02:36 PM   #14 (permalink)
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I'm afraid the lenghwise runners - to force the panel down below the exhaust near the center line - would probably becomes a case of what my Dad called in Yiddish "tzimmes machen". Basically, it indicates a huge amount of highly detailed work or analysis, to the point where you can't tolerate doing it. I'm leaning towards flat panels with simple cutouts for the exhaust low points.

The rails to drop the panels' center line would create their own protrusion, and would require a good bit of effort to fasten the rails to the underbody and then to fasten the panels securely to the rail. I think T-nuts would work with something like a 2x2 (which is actually smaller than 1-1/2" square), but it would still be a pain to build.

Tzimmes is a Jewish baked sweet dish. Lots of cutting and a two-stage cooking process. Typical recipes could include some or all of these: carrots, raisins, plums, celery, onion, potatoes, sweet potatoes. All of these cut up into small bits and stewed together, with sweeteners such as cinnamon, honey, brown sugar. After stewing, bake in a pan. Not a quick process, usually.
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Old 04-05-2018, 05:54 PM   #15 (permalink)
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Today I did a bunch of prep and reconnaissance under the car.
It was pretty cold - with wind chill, it felt like 35 F. Progress should pick up when the weather gets warmer, hopefully soon!

I measured the positions of the added fastener positions in the aluminum front panel, and marked them on the underside of the panel. So when it's back in I'll be able to measure out the locations for the holes in the first coroplast sheet. And I reinstalled it. All the well nuts are in, held in place with screws and washers. The coroplast panel isn't ready yet.


I got both oem plastic aero/protective side panels off, and removed the fasteners along the rocker panel bottoms. So the new panels can get tucked under the rocker panels' inner lips.

Those fasteners like to break on removal; they're old. I maybe can get similar replacements. Or since their holes are 10 mm diameter, (rocker panel mount holes) I can use well nuts made for #10 screws, similar to the #8 well nuts I used in the fastening points I added to the aluminum belly pan.

As Ecky and Natalya did, I'm planning on spanning the sheets across the car. The joints between pieces will run crosswise. I plan to fish scale the joints - overlapping in the direction so the air can flow over it. I'm not going to try for butt joints.

I also made measurements for the first (forward) coroplast panel.
It needs to be 46" wide by 24" front-to-rear. That will reach from the row of mount points I added to Scott's belly pan, going back to the first four mount points originally used for the oem panels. Those are M6 screws, with 10 mm heads. It won't cover the full width of the car at the firewall but that's OK.

I have 3 coroplast sheets, 48" x 96".
I will cut one down to 48 x 70.
That leaves a piece 48 x 26.
That will be my front piece, that needed to be 46" x 24". A couple extra inches will be fine. I doubt it will matter which direction the coroplast channels run.

As for the remaining piece - 48 x 70:
In the area between the firewall and the rear bumper, the maximum width I found that I'll need is 68". That's at the firewall, it tapers narrower as it goes back. So the 70" wide piece I'll make is planned to be able to span that width.

Last edited by brucepick; 04-22-2018 at 09:19 AM..
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Old 04-21-2018, 11:15 PM   #16 (permalink)
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I've numbered the panels for reference in this thread.
All panels are overlapped (front one below the rear) like shingles or fish scales. The overlap joining #2 and #3 is large, due to the locations of the existing available attachment points. They're not in an even line going across the underbody.

Panel 1: The oem front panel section. Aluminum + rubbery plastic.
- Or in my case, the aftermarket aluminum replacement panel, by Scott. AKA klr3cyl on Insight Central. It replaces the aluminum plus rubbery plastic oem front section.
Panel 2: Goes from the rear of #1, to about a foot rear of the firewall.
Panel 3: Goes from the rear of Panel 2 (a foot rear of the firewall), to a point about a foot forward of the rear wheel wells. About 48" lengthwise.
Panel 4: Goes from the rear of Panel 3 (about a foot forward of rear wheel well), to the crosswise narrow air deflector that's mounted at the rear of the gas tank. Air deflector = attachment point.
Panel 5: Goes from the air deflector at rear of gas tank, to the rear bumper lip.

Last edited by brucepick; 04-23-2018 at 01:14 PM..
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Old 04-21-2018, 11:34 PM   #17 (permalink)
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Nice work, Bruce. Lots of good homework, measuring, and thoughtful installation work. Me like.
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See my car's mod & maintenance thread and my electric bicycle's thread for ongoing projects. I will rebuild Black and Green over decades as parts die, until it becomes a different car of roughly the same shape and color. My minimum fuel economy goal is 55 mpg while averaging posted speed limits. I generally top 60 mpg. See also my Honda manual transmission specs thread.

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Old 04-22-2018, 01:57 PM   #18 (permalink)
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I have more posts coming.
I just finished cataloging 22 photos for this thread.

I finished off this project during the seven days April 5-12, just in time to drive up to the Green Grand Prix. I took a number of photos but had little time until this weekend, to catalog them and upload them to Google Photos for use in this thread. I'll come back to this again as time permits.

I'll have some details on such captivating topics such as attachment, sag prevention, and aero smoothing of the joints between panels. I leaned towards methods that would not be too time consuming but should give a sturdy and aerodynamically clean result. I don't claim to have done the best job possible but I think it's a good job.


Last edited by brucepick; 04-22-2018 at 09:36 PM..
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