First project

[BHarvey]

Air dam or smooth under body?

The question is which is more efficient?

The air dam is easier and would keep air from getting under the car especially if combined with skirts, but wouldn't the increase in frontal area negate the advantage?

Looking for which route to go on the first project.

[d0sitmatr]

it depends on what the underbody and stock frontal area looks like now.

[BHarvey]

The under body is pretty tightly packaged on the car with nothing really protruding into the flow. CD on this car is rated at .28 and it does get great mileage, but as we all know, more is better. Car is a 2011 Sonata (manual).

[d0sitmatr]

if the under body is fairly smooth, Id start with the larger frontal dam. then the under body.

[BamZipPow]

Looking at that...I would work on front grill blocking first and then shoot fer the belly pan next...

[euromodder]

Adding a dam doesn't rule out a belly pan.
Air gets underneath the car anyway, so a belly pan still helps even if you have an airdam.

Looking at low-angle pics, the front spoiler seems to extend as low as any other part underneath, with small deflectors in front of the tyres.
If so, go for the belly pan.

[3-Wheeler]

My vote is go for the belly pan!!

Belly pan how-to

Jim.

[aerohead]

Originally Posted by BHarvey

The under body is pretty tightly packaged on the car with nothing really protruding into the flow. CD on this car is rated at .28 and it does get great mileage, but as we all know, more is better. Car is a 2011 Sonata (manual).

Hyundai has already picked most of the low-hanging fruit.If you've had a look at Ford's Probe-IV of 1984,then your aware that there is still some wiggle room on the Cd with respect to the front of the car.
Since the Sonata is as clean as it is to begin with, you're not going to see the gains as if it were a pickup.
My recent experience with the T-100 is that the nose mods accentuate the belly.
Getting the air over and around the car is better than letting it go under even if it has a perfect underside.You already have ground clearance issues so you'll have to be especially careful with ground strikes.
Your cooling inlets have also been trimmed by Hundai,so you have to go carefully there also.
For 'significant' gains you're going to have to go after the back of the car at some point.And for that to work,the sides must be cleaned up.
The short of it,is that you,or anyone else is going to have to follow basjoos' AeroCivic lead.Short of moving the cooling system to the rear of the car he has essentially tackled all the 'issues' the air had with the Civic.And as you can see he's been well rewarded.
At Cd 0.28 you have a better starting point.
The aero-mods Sticky may give you some idea of what certain mods have done for other cars and you can work from there.
It would be good to have a target Cd or highway mpg to be shooting for.

[BHarvey]

MPG, according to the computer, which is always reading 2-3 mpg high, shows...
45 mpg at 55 mph
41.5 mpg at 60 mph
38 mpg at 65 mph

Target is the 45 mpg (which is really 42-43 mpg) at 65 mph.
Under belly was an option.
Lower air dam with side skirts to channel flow away from getting under the sides and also to channel flow away from the rear tires.
Moon covers and mirror deletion should be fairly easy also.

Heck, if it takes all these mods to reach my goal, and hopefully then some, then so be it.

[aerohead]

Originally Posted by BHarvey

MPG, according to the computer, which is always reading 2-3 mpg high, shows...
45 mpg at 55 mph
41.5 mpg at 60 mph
38 mpg at 65 mph

Target is the 45 mpg (which is really 42-43 mpg) at 65 mph.
Under belly was an option.
Lower air dam with side skirts to channel flow away from getting under the sides and also to channel flow away from the rear tires.
Moon covers and mirror deletion should be fairly easy also.

Heck, if it takes all these mods to reach my goal, and hopefully then some, then so be it.

B,I noodled your numbers and here's what I got.
To go from 38,to 45 mpg at a constant 65 mph cruise is an 18.42 % delta-mpg.
Between 55 mph and 70 mph,I guestimate that any 10 % drag reduction will net you a 5.5 % mpg increase.
To get the 18.42 % would require a drag reduction of 33.5 %,or,Cd 0.186.
So your target is 0.186,close to the 1996 GM EV-1.
There's no physical barrier to get you there,although it will require a pretty comprehensive mod list.
Do the nose mods and lets see where you end up,but be thinking about the AeroCivic.