Aerocivic - how to drop your Cd from 0.31 to 0.17

[greenitup]

that is a great idea, it improve fe and is making a statement.
are all of the parts securely fastened and sturdy , ie any vibrations at high speed?

[basjoos]

My stock 70hp engine wore out at 245,000 miles, and it was cheaper to replace it with a used 103hp engine from Japan than it was to rebuild the original engine. The new engine was more powerful than the original, but gave me the same mileage provided I didn't run it up into the higher rpms while accellerating. Before I aero modded it, my 0-60mph with the new engine was 10 sec, and I haven't done any timed 0-60 runs since I aero modded it. Since aero modding it, acceleration in the 60-100mph range is MUCH improved, acting as though the car had been given a significant horsepower boost and the faster I go, the more noticable this boost. The transmission is the stock CX/VX gearing.

I live on a dirt road and the washboarding hasn't caused anything to come loose in the 2 years I have been driving my car with the mods installed. Also no vibrations at high speed.

[MazdaMatt]

Thanks for the info regarding your highway acceleration. I found this site while searching for undertray information for my race car. It has the "crappy" (for racing) high gear ratio tranny, and the crappy (for racing) D16 motor. The next track I'm going to is a 2.5mile road course with very high minimum speeds. I'll be using some of your tech to keep accelerating at high speeds

[wyatt]

Eventually I plan to automate the door by using a Basic Stamp or similar process controller to monitor the coolant temps and adjust the opening to the actual cooling needs.

If you want to automate the door you may be able to have it open whenever the fan kicks on and close afterward. I know in my car the fan kicks on after the coolant temps reach 202degF and it kicks off below 190degF. That's what I plan on doing after I get around to it.
I am new to the site, and I don't even have an MPG meter yet (my first planned modification). Then I want to start making incremental changes and record what the effects are (that's what being an engineer will do to you).

[wyatt]

Originally Posted by Bicycle Bob

I wonder if dust is shaking off that surface.
I'd be happy to observe under-tail tufts for you if we were neighbors, but perhaps the easiest do-it yourself approach would be to tape a digital camera under the tail. Even a very basic one will usually make movies a few minutes long.
I've heard that another quick test for turbulent/laminar flow is the speed of evaporation. If you wet your car and drive a bit, the last wet, shiny areas have laminar flow.

Another method (which I have been thinking about) would be to use baby powder (or equivalent) and pat it down on the surfaces you want to check. Then drive at the speeds you want to check and Presto!, if it gets cleaned off, laminar flow! So if you live on a dirt road and your car stays nice and clean, chances are, you have good laminar flow the entire way.

[basjoos]

Originally Posted by wyatt

If you want to automate the door you may be able to have it open whenever the fan kicks on and close afterward. I know in my car the fan kicks on after the coolant temps reach 202degF and it kicks off below 190degF. That's what I plan on doing after I get around to it.
I am new to the site, and I don't even have an MPG meter yet (my first planned modification). Then I want to start making incremental changes and record what the effects are (that's what being an engineer will do to you).

The radiator door needs to open up before the fan has to kick on so you can avoid adding its electrical load to the engine as much as possible. Ideally you should adjust the amount of cooling drag (radiator door opening) to reflect the amount of cooling actually needed by the engine, which can vary depending on engine's power output, airspeed, and ambient temperature. That's why I want to regulate the door's opening by the temperature of the coolant arriving at the radiator.

[basjoos]

Originally Posted by wyatt

Another method (which I have been thinking about) would be to use baby powder (or equivalent) and pat it down on the surfaces you want to check. Then drive at the speeds you want to check and Presto!, if it gets cleaned off, laminar flow! So if you live on a dirt road and your car stays nice and clean, chances are, you have good laminar flow the entire way.

You would be surprised at how thick a boundary layer actually is. I've sprinkled Florida beach sand on the top of my car and driven down the road. It would still be there when I got to my destination, unless I drove through rain. The road dust doesn't stick to my car while I driving down the dirt road, but if I parked my car beside the dirt road and let it sit there while passing traffic stirred up and settled dust on it, then that dust would stay put when I went to drive my car again.

[greenitup]

does it fit in a standard parking space?
also did you experiment with different boattail lengths?

[greenitup]

also do you have problems with engine temperatures or does the front end not block the entire grill

[basjoos]

It fits in a standard parking space. I didn't experiment with different boattail lengths. I used the tailcone of a Questair Venture kitplane (a 350mph airplane nicknamed "the flying egg" for its short fuselage) as a pattern in designing my boattail and just sized a pattern for the Venture's tailcone to fit the back of my car. I have a small air inlet slit at the top of the nosepiece that feeds air to the radiator. The only time I have ever had any overheating problems was when driving 75+mph on a 95F day. No problems in normal driving, even when climbing up US25 into the NC mountains. One of the things on my list is to install a manually operated radiator door in the front of the nosepiece.

View of the front and the air inlet slot (at the front of the hood on the passenger's side).