Can front air dam hurt mpg

[SmellyCat]

I attached some black landscape
Trim below the front trim under the bumper. Is there any chance I
I would improve mpg by letting the air go under the car? Yes or no. Sc

[Gealii]

if not installed properly yes and air dam can hurt mpg. now improper installment can range from being the height of the air dam is to tall, the air dam is to far back, the list goes on.

[Piwoslaw]

The purpose of an airdam is to keep the car's aerodynamically dirty underside (and front tires) out of the airstream, increasing frontal area to reduce Cd. So if the airdam is taller than needed then you will be wasting energy to push air.

If the underside is already smooth then an airdam will hurt CdA. Wheel spats would be enough in that case.

A-B-A-B testing will answer the OP's question.

[SmellyCat]

Ok since it's a Volvo station wagon 1994, I reckon it is helping. Abab testing is not going to work since the speedo odo. Stops working now and then. Damimg the air flow under the front bumper does not make as much sense in my brain has the front grill block does. Sc

[KamperBob]

I agree an air dam could hurt MPG. In free flight a streamline body has nominal low Cd. In ground proximity its Cd goes up substantially. If a chin spoiler adds frontal area then unless it somehow reduces Cd enough to compensate then it seems reasonable to expect CdA to increase. To my mind just cleaning up under belly seems more likely to improve Cd and Cda. Just my 2c...

[SmellyCat]

Here is a front Picture, I lowered the front dam 3-4 inches. SC

[kach22i]

Originally Posted by SmellyCat

........Abab testing is not going to work since the speedo odo. Stops working now and then. .........

One major benefit on the two trucks and one car I have installed front air dams (chin spoilers) to is the decreased buffeting during heavy cross winds on the highway.

I believe in all three cases hwy mph went up about 1.5 mph.

However, there are several reported cases in the forum of decreased mpg with the use of large chin spoilers/air-dams.

[nemo]

This is the 1st attempt and measurement on my car it is now only 1/4" bellow the cross member. Don't go any lower than where you determine the most of you drag to be coming from. So take a look, determine how much is if any thing is below your factory dam and adjust accordingly.
You may have noticed that some of the factory dams are higher in the middle, I believe this is two fold one to keep the frontal area as small a possible and still redirecting the air flow around lower hanging components.