undertray cover and air dam?
 

I've been reading up a lot on everyone's post on these two subjects. I have a few questions though.

Although I'm tempted to cover the entire underbody with the underbelly pan, I don't want to restrict the air flow out of the radiator. Usually, without the pan, the air escapes underneath the car. Although not the most efficient in terms of drag, it does not restrict it.

I think I'm going to only install the pan on the front portion of the car. Would you guys agree?

Now... if you already have an underbelly pan, how much does an air dam contribute to the overall drag? I usually see the dam on cars without a smooth underbody. It seems to be a shortcut to achieving something similar to the pan but in a different way.

Any opinions?

Installing the underbelly pan in the front of the car will hinder airflow out of the radiator - that is where the radiator is. That being said, install it anyway and watch your oil and water temps, you can always open up the back of the pan to let some additional air flow through the engine compartment.

Correct, however adding an air dam increases frontal area. Best FE setup would probably be only the underbelly pan to smooth airflow and minimize frontal area. Air dams are easier to install and make servicing the vehicle easier than a belly pan but the benefits MAY not be as great. Do an experiment, a good data point would be great for us all!

I think that even if you covered the whole underside, a lot of the hot underhood air would escape out through the wheel wells. At least on my car...

On my car, a 92 Civic CX hatch with a DX engine, I have a complete smooth underbody panel and exhaust most of my radiator air out through my front wheel wells. The remainder exhausts out through the central tunnel that the exhaust pipe runs through (where it cools the cat and exhaust pipe) and exhausts into the right rear wheel well. I have been running it like this for a year and a half without any overheating problems in South Carolina summers, dispite having a grill block and front wheel well skirts installed. I don't have a air dam. Installing the underbody panel reduced the road noise inside the car, apparently a lot of "road" noise is actually wind noise being generated underneath the car. My underbody panel is mostly coroplast with aluminum roof flashing covering the areas near the exhaust pipe. With all of the aero mods on my car, I have no problems getting over 90mpg at 65mph on a flat road in the summer. Since most of my driving is on interstates and rural roads, I've optimized the aero on my car to give good FE at normal interstate speeds.

Awesome guys! My most recent fillup gave me 50MPG. I drove mostly 60mph and occasionally going 55mph on the freeway. This is the best I've ever done.

I used to drive 75 to 80mph all the time. I used to get around 37mpg. Now I get better FE and a feel a lot calmer not having to go around slow people :)


One more question for you guys...

I read somewhere on the forum that the optimal ride height is around 2.9" off the ground. Can anyone state whether there is any evidence for this?

Thanks a bunch. I need to look for some material to use for my underbelly pan now.

Chrysler did some wind tunnel tests with a 300 a couple of years ago with belly pans. What they did was cover under the engine but place ductwork to the rear to allow engine heat to exit. What they want to do is force the air to exit the underside of the car in such a way as to affect the turbulence in a way that they wanted. Photos attached.

secure that belly pan tight, altimas/maximas are coming in all the time, customers hit one of those parking curbs, it rips out most of the plastic clips and the cover either falls off or hangs down and gets torn up. usually the customer blames the dealer who did a oil change but the plug/filter is no were near the front of the car.