Flat Bonneville-type spoiler

[cfg83]

California98Civic -

I did an overlay and I came out with the same answer, center of camber over the B-Pillar :



CarloSW2

[vskid3]

Could someone make an overlay with the sedan version of the same generation civic? I haven't been able to compare my sedan side by side with a coupe, but I believe california said the rear window on the sedan is steeper.

[PaleMelanesian]

Here's an overlay of the sedan vs coupe. The rear window is indeed steeper, and the trunk is a different shape. Both of those mean we would want a longer spoiler.

Watching the morning dew evaporate, I conclude that my sedan has detached airflow from about halfway down the rear window. The bubble makes an arc from the lower corners up to the center of the window and back down.

(I don't know what's up with the front wheel. I took both images from Tirerack's "buy wheels" preview and photoshopped to get the outlines. I matched the rest of the body and had to ignore the front wheel)

[cfg83]

vskid3 -

Originally Posted by vskid3

Could someone make an overlay with the sedan version of the same generation civic? I haven't been able to compare my sedan side by side with a coupe, but I believe california said the rear window on the sedan is steeper.

I did this :



At first my center of roof camber was in the middle of the rear window. However, it seemed like the template had a better fit when I moved it a bit forward. Then, when I overlayed it with the coupe, it lined-up very nicely. Therefore I think this overlay is "good".

CarloSW2

[vskid3]

Thanks for that, cfg83.

Originally Posted by PaleMelanesian

Watching the morning dew evaporate, I conclude that my sedan has detached airflow from about halfway down the rear window. The bubble makes an arc from the lower corners up to the center of the window and back down.

Attachment 8472

So one could possibly start a kammback or boat tail from halfway down the window and still get good results?

[California98Civic]

PaleMelanesian... the Sedan should also be slightly higher, according the specs I have seen. It has a slightly different profile as a result. I think the template might need to shift a bit, though I am not sure if it would be forward or backward.

Viskid... I posted a link to the complete shop manual for our 96-00 civics... search the manual on this site and you'll find the link. In the manual there are Honda's profiles of the Sedan, the Coupe and others for which the manual applies. That is where I got the image for my overlay. I used the select tool in Adobe, and then pasted it into a Paint.net freeware doc for the overlay (MSPaint won't do).

I tested the spoiler tonight, with somewhat disappointing results.

[California98Civic]

I tested my spoiler on a 6.2 mile stretch of freeway this evening. I got to speed (55/56mph) and throttle position (16.5) before pressing reset on each run. I held 16.5 throttle throughout, allowing speed to fluctuate on hills.

I made A-B-A-B runs. Each "A" and each "B" includes a trip 6.2 miles north and another south. Average of all "A and all "B" runs:

A (no mod) = 49.55
B (modded) = 50.15

Attached below is what the spoiler looked like during the test.

PROBLEMS: The test was not ideal. A modest crosswind kicked up in the middle of my runs, and I seemed to attract trucks like a giant magnet on a few runs, forcing me to eliminate an outlier run completely and repeat it. Also, despite being on the freeway, hills and my throttle position meant that my speeds dipped to 45mph once in each direction. Often I was driving 52/53 mph. Those are speeds not much better than my earlier 52mph quickie tests. But I was often in the 60-65 range too. Lastly, a small part of the underside support (seen resting on the bumper in the photo below) got ripped-off by wind on the last run, which makes me wonder about vortices and such *under* the spoiler. Who knows...

These results largely confirm my quickie tests on previous nights, and even suggest that higher speeds would still mean greater benefits for FE. But this is a big, long spoiler! Two feet extension. Seems like a too-marginal gain for such a conspicuous mod.

I want to try a smaller design, with a mild, upward angle of a few degrees. I don't think I want to build anything more permanent in this form, for these gains.

[PaleMelanesian]

You are correct. The Sedan is 54.7 inches while the Coupe is 54.1 tall.

Thanks for the service manual download, too.

[California98Civic]

Originally Posted by PaleMelanesian

You are correct. The Sedan is 54.7 inches while the Coupe is 54.1 tall.

Yeah, sorry, it's a more minor difference than I thought. But is the highpoint a little further forward? Would it not matter?

[Big Dave]

0.6 MPG may not be dramatic, but ecomodding is often the quest for a long series of small victories.