Aerodynamics and drag coefficient

[hotroddr]

I have done my share of testing of aerodynamics with my cavalier test mule. It has shown a sizeable increase in gas mileage since the modifications were done. Here is a pic for reference. You may not like the look but everything you see is in the name of aerodynamics.

I covered the grill first with cardboard to determine if it was worthwhile and if the cooling was needed. I found that it did help increase fuel mileage(hard to say how much exactly since I did a lot of things to it for that trip). It also gave the steering a stiffer feel on the freeway. I realize these findings are very unscientific but there was a noticably more solid steering feeling with the grill covered. It ran 20* warmer on the freeway with no increase in temperature on hills. It will heat up a lot in traffic but as soon as the electric fan kicks on its ok.

To comensate for the reduced cooling from having no grill, I decided I could redirect the air that was going under the car through the radiator with an extended and stiffened air dam. The air dam is about an inch and a half lower than it was before and is reinforced with plastic angle to prevent it from collapsing too easily at speed. It is also designed to scrape wherever it wants without falling off. This dropped the temperature 5* from the original operating temp, or 25* from the temp with the grill covered.

The weird looking flaps hanging down under the bumper were intended to direct air around the tires to avoid the turbulence associated with air hitting a spinning tire but I could not tell any difference in feel or gas mileage. I would tend to say its not worth the effort but this was the only configuration I tried and I didnt eliminate enough variables to be sure. They might be more worthwhile on tires bigger than 215s.

I then removed the plastic shields that went between the wheelwell and the engine compartment and the wheelwell to allow engine compartment air to exit the wheelwell. I didnt notice a huge improvement but I think there may have been a little. I did make an interesting observation though. I first removed a piece that blocked air from the front from going around the radiator and noticed a definite decrease in steering feel at speed. I figure this is from the air going through the ex fog light holes bunching up in the wheelwell/engine compartment causing lift. Pics would help you visualize this but I dont have any.

I removed my windshield wipers which improved the looks a little and when it rains the rain blows right off probably because of the smooth air flow without the turbulence produced by the wipers.

The goofy mirrors are from a yamaha R6. I looked at a bunch of different mirrors and found these to look the most aerodynamic. They are not ultimate but Im sure they are better than stock. The stalks are fairly long to keep the flow seperation away from the boundary layer of the body of the car. The stalks are also streamlined and angled towards the back of the car. The body of the mirror is also very smooth. My qualm with these is that the inside part of the mirror body angles towards the window which makes for more noise than if it angled away from the window.



I used to get about 30mpg at 80mph on flat ground and now Im up to 38 mpg so I would say that was a success. You opened a can of worms by starting a discussion on aerodynamics with me. I find it endlessly intriguing. On the list of future tests and experiments with meaningless results: Rear diffusers/venturis, belly pans, rear lips/spoilers, front splitter lengths, vortex generators, speed varying ground clearance and spoiler angle and height, and vents behind the wheelwells for letting out high pressure air from the engine compartment.