Air dam - good or bad ?

[holypaulie]

Is air dam increase or decrease air resistance ? This guy says that air dam increases wind resistace from more frontal areahttp://www.hydrogen-boost.com/May%202005.html

[Hockey4mnhs]

It stops the air from going to a very un aero friendly part of the car (under it) and it goes around or over the car instead.

[unstable bob]

If you read the link that Paulie posted, the guy says that an airdam caused more wind resistance and lower mileage...hmmm, I thought an airdam was a good mod, and I have one on my to-do list.
Hey Paulie, what part of NJ are you from? I'm between Exits 9 & 10. lol

[holypaulie]

Originally Posted by unstable bob

If you read the link that Paulie posted, the guy says that an airdam caused more wind resistance and lower mileage...hmmm, I thought an airdam was a good mod, and I have one on my to-do list.
Hey Paulie, what part of NJ are you from? I'm between Exits 9 & 10. lol

I'm close to Exit 4

[Bill in Houston]

It is possible to make a bad air dam.

[skale7]

I suppose if the dam looks like a snowplow, then yes, it probably hurts mileage.

[lca13]

An air dam with an 8 inch drop is not gonna help... too much. What you are looking for is smooth underflow.... or to decrease the turbulence some if not (so avoid any head on air to car collisions underneath).

I would try these guidelines:

Look underneath the front, level with the lower bumper.... any obvious non-smooth underbody surfaces should stand out. A dam to redirect air away from them helps.

Look at other cars that have tried air dams for mileage purposes.... the Civic VX for example has one... but it is surprisingly non-instrusive (almost nothing in the middle with a slight slope down towards the tires).

Nascar's use of airdams is more for preventing lift than anything else... a typical race car has a fairly high Cd for that reason.. they just power through it.

In the back of your mind remember that, unlike in a wind tunnel, real driving has the air near the road not moving, instead of blowing by the car at 50 mph. A big air dam changes this by carrying more air with you as you drive, unlike what you really want to do, which is streamline the underneath w/o adding surface area, so as to affect as little air as possible.

[varg]

It has been established that an air dam is a compromise. If too small, it will have almost no effect, if too large it will increase drag. The size of your air dam should be calculated to make less drag than the underbody of your car does (and that could prove tricky). This is to say, that if you had a .35cd stock and a .32cd with a completely smooth underbody you might get .33 with an air dam because even though it reduces drag under the car, it still creates drag itself. This is where a belly pan comes in handy, because it purely reduces drag under the vehicle instead of reducing it and in then adding some back itself like an air dam.

Originally Posted by lca13

In the back of your mind remember that, unlike in a wind tunnel, real driving has the air near the road not moving, instead of blowing by the car at 50 mph.

I dunno about that, sounds like point-of-reference confusion to me.

The car moving through the still air (driving) is the same as the air moving over the still car (wind tunnel)

[lca13]

>>The car moving through the still air (driving)
>>is the same as the air moving over the still car (wind tunnel)

The difference is that in once case, the air is stationary WRT to the ground, and in the other case it is moving. Put the car way up in the air in the wind tunnel and you do have the same effect, but as you lower the dam towards the ground, things will be different.

Not that it matters in this discussion, but to me it just helps to think in that reference, instead of the usual "air is blowing by the car at 60 mph"... so I think instead, "My goal underneath is to disrupt as little air as possible, how can I do that?.... noting that blocking more air up front with more surface area is generally a bad idea".

[Philip1]

Look under your car anything that hangs down will cause drag tuck everything up as close as you feel comfortable to the floor. Ultimately you want a perfectly smooth belly this can be accomplished with a pan but that requires extra effort... Are you willing?