Aerocivic - how to drop your Cd from 0.31 to 0.17

[basjoos]

Stan, thank's for the side skirt analysis. I'll have to play around with various configurations after the weather warms up and the temps become more stable. Its hard to see the results of an aero change this time of year when the high temp one day is 70F and on the next it is 30F.

[archi_jbg]

I was really intrigued by the level to which you have taken this civic and most compliment you on that. I was wondering if to any degree you have changed some things involving the engine as well. I have found that adding a cold air intake, larger spark plug wires and platinum 2 spark plugs that i have been able to go from 28 mpg highway to 32 mpg highway. (1994 accord) Just wondering what peoples approach has been.

[basjoos]

I've rerouted the radiator cooling air flow. Also the grill block and underbody paneling have increased the intake air temperature, so I have the equivalent of a warm air intake, but I haven't yet changed anything on the engine itself. That would be a whole entire area to investigate.

[claytori]

It is quite fascinating to see a Honda Civic morph into a Citroen DS-21.

[MitchJi]

Originally Posted by basjoos

Cd reduction would work to improve the high speed performance of any car and is what they do on the Bonneville Salt Flats to increase the speeds of their speed record cars. Since aerodynamic drag is the dominant load factor at higher speeds, the faster you go, the more you'll notice the effects of a low Cd, reducing the amount of power you need to travel at that speed and in effect acting as the equivalent of a horsepower boost at the higher speed. As far as fuel efficiency goes, a low Cd extends the range of speeds where you can still get good fuel economy into the higher speed brackets and a low Cd car will get better fuel economy than an otherwise identical high Cd car at any speed above 30mph, the difference becoming more and more noticable the faster you travel.

The hand accelerator is set up the same as the one on my John Deere tractor (the hand control sets a lower throttle position that can be overidden by pressing on the foot accelerator. The hand throttle only goes from zero to slightly above half throttle and I have trained my reflexes to automatically pull back on the hand throttle whenever I push down the clutch pedal. On the rare occasions when I do forget to pull back on the hand throttle when I push down the clutch, the engine just revs up and reminds me I need to pull back on the hand throttle.

Hi Basjoos,

Great job!

How big a difference in fuel economy do you think your mods make at 50 or 55 mph?

Which 5 or 10 modifications do you think helped the most (in order of effectiveness if possible)?

Which 5 or 10 modifications do you think produced the most effect with the least work?

Your DWL hand throttle gets overridden by the foot throttle. How hard was that to set up? How hard would it be to make the brake and clutch turn off the throttle?

Thanks!

Best Wishes ,

Mitch

[diesel_john]

basjoos, in post # 44, I would have curved the rear boatails the other way. (convex) was wondering if your design is based on the salt patterns. John

[basjoos]

Mitch, Since I didn't have a SuperMId when I started this project and added the mods piecemeal over a period of over a year, I don't know for certain how much of an effect my mods have at any given speed, just that the faster I go, the greater the effect of the aero mods. But the improvement in coasting starts to become noticeable at speeds over 35mph. It would be interesting to drive my car and a stock CX (both equipped with SuperMID's) side by side and see what the differences are.

Mods in order of efectiveness: 1)boattail, 2)reshaped nose with grill block,, 3)underbody panelling, 4) front wheel well skirt, 5) rear wheel well skirt, 6) Reshaped windshield, 7)rear wheel boattails, 8)front wheel spoiler, 9)side skirt, 10) internal rear view mirrors.

Mods of most effect with the least work: 1)reshaped nose with grill block, 2) rear wheel skirt, 3)front wheel spoiler, 4)side skirts, 5) Rear wheel boattails, 6) internal rear view mirrors, 7)windshield wiper air deflector, 8) smooth hub caps, 9)front wheel well skirt, 10) underbody panelling.

Overridding the DWL hand throttle with the foot throttle is simple and functions identically to the way it does on a tractor. The hand throttle sets a lower limit for the throttle while the foot throttle can override it to force a higher throttle level if you need to pass or maintain speed on a hill. Mechanically, the hand throttle is a simple pushrod that presses against a metal plate screwed onto the accelerator pedal. Making the brake and clutch turn off the throttle would be more difficult, as you whould have to pick the signals off the brake light circuit and the clutch travel switch and use them to energize a solenoid that would disengage the throttle cable. This would be tricky to do.

diesel john, I made the rear wheel boattails assymetric to help curve the airflows inward so they could help to fill the expanding space under the boattail. The angle on the bottom side of my boattail is somewhat sharper than the ideal since I didn't want the boattail to drag on the ground while entering my steep driveway. The inward angling of the wheel boattails helps to compensate for this slight aerodynamic flaw.

[MitchJi]

Hi basjoos,

Thank You Very Much for the detailed reply.

Best Wishes ,

Mitch

[diesel_john]

thanks basjoos, good info. Is the hand throttle like constant throttle position cruise or how is that used? diesel

[MitchJi]

Originally Posted by basjoos

More pics:
Side skirts made of coroplast (there are 2 side skirts on each side, one even with the inner edge of the tires, the other even with the outer edge of the tires).

Hi Basjoos,

So the skirts look like this from the end view (dashes on the left are needed to get the skirts inside the outer edge on this page)?:
|___________________
-----| |

Would something like this be better (connect the side skirts to the sides and the middle skirts to each other)?:
| __
|__| |___________|

The side of the car would connect to the side skirts with one smoothe curve rather than have the side end and the skirt sticking out.

Connecting the sides to the skirts and to each other would increase the frontal area a little but there might be less turbulence.

Best Wishes ,

Mitch