1999 Acura EL or Civic EX sedan - dropping Cd from 0.33 to below 0,20

[ACEL]

Fantasy as the required data to assess the benefit of the modification was not recorded.

Part of my work on the car is looking at newer cars style and devices to compare it with scientific literature and ecomodders experiences, looking for benefitting opportunities. Thus 6 modifications were fabricated in 2019 with little performance assessment on the aerodynamics benefit.

These are
1. Upper grille block with an attempt to streamline
2. Behind rear wheels under belly
3. Air dam
4. Rear trunk lid spoiler
5. Lower side skirts
6. Front spoiler

Some mods are not easy to mock-up with cheap materials like cardboard and tape. In retirement, the available money is scarce. Also, aesthetical constraints and life partner regard on the work done are limits.

Upper grille block with an attempt to streamline

Some aluminum left over from building renovation was modeled to completely block the upper front grille. It was then painted black to match the car color. It was attached at its bottom with two screws in the licence plate holes. At the top, under the hood lid, it was just taped with the "big monkey" fabric tape.

The engine coolant temperature went up from the 70s and lower 80s Celsius to the high 80s and 90s with was intended as an added bonus to the aerodynamics improvement. It seems that engine coolant temperature in the range of 90-95 Celsius is the best for the most complete combustion of the fuel load.

Behind rear wheels under belly

Having some thin aluminum left overs, a sort of rear diffuser was built before the car went out of winter storage. I am no manual worker and certainly not a good craftsman. Pieces were joined together. The whole pan was curved and baling down without enough support. The diffuser angle was in the 1-2 degrees slope at most. The rear car tow hook was hidden and lost. Bad work.

Air dam

As many ecomodders, a 4 ½ inches lawn edging was used to build a front air dam. As on other cars, it was recessed from the front of the bumper cover and almost invisible. It probably brought some mileage improvement that was not seriously assessed. It was replaced by the front spoiler discussed further. Total cost below 10 Cdn$ including self taping screws and sales taxes.

Rear trunk lid spoiler

Looking at 8th generation Civics and Civic hybrid, adding a trunk lid spoiler seemed like a good idea. At first, it was a mock-up. Three layers of 4.5 inches lawn edging were piled up with the next coat rounded edge exceeding the previous, thus building up height but also a rear end slant. Each lawn edging coat was taped with the “big monkey” fabric tape. For a cheap mock-up, it was looking fairly good. It did not pass the aesthetical assessment.

The mocked-up trunk lid spoiler was replaced by a real OEM one from the junk yard. It was taken from a black 8th generation Civic (2006-2010). It remains on the car even though it has not been assessed.

The junkyard cost is 15 $, some two faces 3M automotive tape for moldings and one tube of black silicone caulking were used. About 40 $ and some leftovers.

Lower side skirts

Low budget right material is not easy to come by. Building vinyl siding board for 10 $ was acquired from the hardware store. Strips 3 inches wide, retaining some cornering material, were cut and joined to the OEM existing side skirts with self-tapping screws. It was also painted black before installation to match the car color.

Unfortunately, the siding vinyl board is not a sturdy material. Whether in making the strips or when screwing through to the side skirt some tearing resulted. The material being soft was easily bent to follow the side skirt contour but was also prone to tearing. These side skirts addition lasted the season but one was so badly damaged that both were replaced for 2020.

Preliminary assessment – 1st third of season

Rear section belly pan, air dam, lower side skirts, and deck lid spoiler were combined and resulted in a combined mileage of 7.3 L/100 Km for 2517 Km (32 mpg US for 1564 miles).

The real interesting result is in the whole lot better car stability to side winds and being passed by a truck and box trailer on highway. The car stays the course or requires much less correction than previously.

Front spoiler

Newer cars like Prius, Corolla, Civic, Sentra, Volt and many others have a front spoiler as the lower part of the plastic bumper cover. It may be just a designer fantasy that was copied by competitor professionals at other cars manufacturers or it may have some aerodynamics value. So, I set to fabricate one with cheap building materials available at the hardware store. Pictures attached represent the fabrication process.

The front lawn edging air dam was replaced by this fabricated spoiler at the beginning of the second third of the season.

The styrofoam 2 x 8 x 2 in. thick insulation board was selected for the core. It was than cut in some resembling spoiler shape. Some ½ inch thick window plastic material was used on top and bottom to add strength to the bumper cover attachment. Each coat of material was recessed from the previous bottom one in order to create steps that would allow for a slanted surface when filled with polyurethane foam. The core and strengthening parts were then installed on the car and joined to the bumper cover with 3 ½ inches wood screws.

Polyurethane foam filling the steps and knife sculpting the spoiler to its final shape were the next steps. Not knowing if the spoiler would stay or hold on, the “big monkey” black tape was applied to make it look as good as possible. It seems that air flowing does not care about a very smooth or somewhat rough surface. To this day, by the end of June 2020, the spoiler holds on and awaits the final fiberglass and body filler that will give it the kind of look that will be acceptable.

The cost for this mod is about 25 $ for the styrofoam 2 inch thick core, 60 $ for the white PVC finish for window, 3 polyurethane spray cans for 20 $ and 21 $ for the largest 2 in. wide roll of the "big monkey" black fabric tape. This is all in Canadian dollars, sales tax included.

2nd assessment

But for the replaced air dam, all other mods remain. The car was driven a total of 5723 Km and yielded 6,73 L/100 km in mileage over that period (35,2 mpg US for 3556 miles). Driving conditions and driving style were the same, most of the time with the same driver.

The mileage improvement over the 1st third is 0,6 L/100 km combined (3 mpg US). The second third of the season started with the highest outside temperatures that require the use of the air conditioner. The 2019 mods although not assessed seriously were effective and are to remain or be improved for 2020.

2020 improvements on 2019 mods

Such improvement includes better more rigid side skirts and complete better built belly pan. Also, the front spoiler scrapes badly and gets damaged frequently. If possible the lower white reinforcements coat will be removed. Also the front "air curtains" found on many newer cars seem to have enough merit to be tried on this car and the spoiler will have to be modified to accommodate for that.

[ACEL]

It seems that separation edges are important in terms of drag and car noise in the passenger compartment. All newer cars and SUVs have separation edges at the rear end. So maybe I could fix the lack of such edges on my 1999 Acura EL and reduce this car drag somewhat.

Folowing indications from Julian Edgar book, I drove many runs on a dusty road. I am at a loss to read the dust deposition and identify the appropriate position of the separation edges. So please, have a look at my pictures and give me your opinion on the position of such edges. HELP! HELP! HELP!

[California98Civic]

I like the build method for your front splitter/airdam. I think it is likely to produce some downforce with that forward and scooping design. It might also lower the press peak point and separation point at the nose? Generally, I think that is considered good. But you would want to try testing to be sure.

That dusty road technique is old, and I think it can reveal useful things. I did some a couple times on the El Mirage Dry Lake LSR site in maybe 2013 and 2019. I find too that morning mist and due settled on my car will blow off in ways that are suggestive, reminiscent of tuft testing results and dust results.

Your results in the pic about suggest a trip line or other separation device might help. You might consider a box cavity type spoiler with side plates like I tested last year. Thee is a very good study on the box cavity that I and others have posted about repeatedly.

Your rear bumper cover seems mostly clear of dust in the middle. Is that correct?

EDIT: I will add this photo from my dust test last summer:


Ridiculous how similar the shape of our cars are. In this shot you can see that without the rear spoiler, dust settled heavily on my bumper cover. When I added the decklid spoiler mockup, this was the result.

[ACEL]

California98Civic - Your observation of the bumper cover is right for this test conducted in May 2020. (first picture attached is from the same series) I missed it. Thank you. There was little dust on the center of the bumper cover. The picture showing the dust on the corner of the bumper cover confirms that. Also, it seems that this dust pile up is directly related to the rear wheel located just ahead.

Second picture from a dust test today July, 2, shows that the situation is changed. Now, the dust piles up on the bumper cover center and much less behind the rear wheels. Modifications realized since the first "novice" dust test are the vortex generators, my take on the rear wheel boat tails, some side skirt deflectors just ahead of the rear wheels and the exhaust extension side oriented (assuming it energizes the air coming up from the diffuser into the wake).

Rear wheel both tails are made from the vinyl gutter leftover originally purchased for the side skirts (5,50 cdn$ for 10 feet length). Funny that I chose the open box design for these boat tails! Vortex generators at the center are the Amazon shark fin type, and the external ones are simple vinyl 90 degrees corner 3/4 x 4 inches while awaiting for more black shark fins ordered.

Green tapes on both sides show the actual locations of flow separation "read" from the dust deposition.

More on the mods later!

Thanks for your useful comments,

Regards,

Real (Acel)

[California98Civic]

Interesting and hard to tell what the changes indicate since there have been a few mods. Do you have covers over the rear wheel wells?

[ACEL]

No covers on rear wheel wells and no wheel covers either (pics). Not yet.

My rear wheel boat tails deflect the rear wheel flow to the middle of the car. So the result of having dust piling up on the center of the bumper cover is expected.


I am looking at the Honda Clarity to build at least the same type of rear wheel well covers.

I will probably have some wheel covers too (pic). I tested some "Tesla" type wheel covers built with pizza pans. (black lettering vinyl bonded to pizza pan) Joining to the wheel was not stable and conduced to wheel balancing problems. I had to remove the covers and think about some other way to secure it to the wheels. Coming soon!

Real

[California98Civic]

This is a very clever wheel cover design. There should be some way to get them right.

[ACEL]

First attempt was zipties

Second attempt was with long nylon toggle bolts

In both cases the wheel covers were moving slightly causing a wheel imbalance. Also the pizza pan edge was damaging the wheel finish.

Next try will be longer wheel lug nuts pierced at center and a nut bonded with epoxy glue, then a machine screw. Wheel covers should not move anymore.

Any other idea?

Real

[ACEL]

Pics are not commented and results from a dust test to determine where to install separation edges.

All comments and suggestions are welcome,

Acel

[ACEL]

After a 2nd dust test, not using water this time, some separation lines appeared.

Some separation edges were fabricated and tested in a 3rd dust test (see pics).

3 firsts pics: On the driver side, there is dust accumulating on the side of the bumper cover behind the rear wheel: this suggests that the air flow is already detached so the dust can stick. There is also some but less dust deposition on the metal panel above the driver side leg of the bumper cover. The wheel and/or the well need some treatment!
Also there is more dust on the side leg of the bumper cover behind the "separation edge" than immediately after.

4th and 5th pics : show dust deposited on the upper flat surface of the bumper cover. Note that there is less deposition near the separation edges: also, these area are right above the rear wheels "boat tails" which deflect some air coming from the wheel directed to the middle under the car.

6th pic shows some dust deposition on the C pillar resulting from a separation around the rear door window.

7th pic shows the passenger side separating edges and some dust deposition.

Did I get these separation edges right? Is the analysis correct?

All comments and questions are welcome. I want to do those separation edges right.

Real

3rd Test: Separation edges V.02

Separation edges location from the side panel above the tail light and on the tail light seem right: little dust deposition before the edges and no dust deposition after the edges.

Looking at the bumper cover dust deposition on the V.01 separation edges got me thinking. If dust deposits before the trialed separation edge, the edge is either forming a ridge that creates a “no flow zone” or is located too far back and flow separates before to get to the “edge”.

Then, I removed the bumper cover questionable edges and as I had to drive for errands, decided to look at the dust deposits remaining after to locate the V.02 separation edges.

From the remaining dust deposit, the bumper cover separation edges were relocated and some fabric tape was added to make a gradual transition of the flow from the side panel to the edge.

There is a few dry days to wait after some heavy rainy days to get the dust moving again to test this V.02 mod.