Air deflectors under car question

10-30-2002, 09:16 AM

Can sombody explain the purpose for the air deflectors that are mounted under the car just before the engine compartment? I assume they aid in the cooling.

Also, I have seen an oil cooler mounted to the fire wall just above the air delectors - any comments about this??

Thanks.

Ken

Paul_Heery · Paul_Heery's Garage

Quote:

Originally posted by 78911
Can sombody explain the purpose for the air deflectors that are mounted under the car just before the engine compartment?

Yes, I can. Other people have also explained it as well.

http://forums.pelicanparts.com/showthread.php?threadid=83527&highlight=air+deflectors

10-30-2002, 12:40 PM

Thanks,

Ken

SummerSledSix · 10-30-2002, 02:52 PM

I'm not sure that thread answers Ken's question. Those plastic flaps mounted on the trailing edge of the floor pan at the base of the firewall do not deflect air upward, they are more like spoilers for airflow under the car. My best guess is that since they are mounted in line with the heat exchangers, they are intended to keep under-car airflow from cooling the bottom sheet metal of the heat exchangers, which would reduce what marginal effectiveness they have to begin with.

derek_sf · 10-30-2002, 03:15 PM

I don't know, I always heard those were for cooling purposes. who knows the real answer? I just sent mine to someone in SJ today.

thesey914 · 10-30-2002, 03:20 PM

Surely these flaps will create a low pressure area under the heads therefore drawing hot air out and down by a vacuum effect?

scg · 10-30-2002, 05:06 PM

Quote:

Surely these flaps will create a low pressure area under the heads therefore drawing hot air out and down by a vacuum effect?

That's always been my understanding. If you leave them off, your temp soars (especially on a six).

Dave at Pelican Parts · Dave at Pelican Parts's Garage

Did you even read the post linked there?

They create a lower-pressure area under the car. This helps suck the warm air out from around the engine, letting the cooling fan push more cold air in. Just like it says in the post there.

--DD

Bruce Allert · 10-30-2002, 10:18 PM

It's like a venturi effect... the same principle is used in hydraulics, when pulling liquid from a source to be mixed with another liquid like spreading herbicide through a garden hose sprayer.
Also known as "suckage"!

thesey914 · 10-31-2002, 02:12 AM

Getting cool air to the bottom of the motor isn't really that beneficial. The deflector flaps are there to make a low-pressure area that sucks the warm air out of the cooling tin to the area under the car. This helps the cooling fan to push more air through the engine more easily

Yep sorry Dave -you already hit the nail on the head.....I only speed -read it.

krk · 10-31-2002, 06:44 AM

Quote:

Originally posted by Paul_Heery

Yes, I can. Other people have also explained it as well.

http://forums.pelicanparts.com/showthread.php?threadid=83527&highlight=air+deflectors

The link DD gave in that thread is also worth reading:

http://members.rennlist.com/chuxter/#TempTests

(I didn't know they came in different sizes -- in his case, he found a 7 degree change by switching from short ones to full size ones)

krk.

URY914 · URY914's Garage

I had to take mine off. They kept dragging the ground and slowing me down.

SummerSledSix · 10-31-2002, 07:15 AM

I think Dave's retort was aimed at me guys, and rightfully so. I also "speed-read" the entire thread, then re-read Rockaria's post looking for deflector wisdom, but missed Dave's last sentence. Guess I should avoid attempts at higher brain function after taking the red-eye back from the Shaky Side

.

Just to burn a little more bandwidth though, I understand the venturi effect those flaps will exploit, but if their function is to promote air circulation around the underside of the engine, why are there 2 little ones as opposed to a single flap all the way across? Chuxter's item #4 would tend to support this under the "more is better" theory...

John Rogers · 10-31-2002, 07:49 AM

I tried making a larger, single flap a year or so ago for my race car and it made no difference from the smaller factory ones. It went about 75% of the width and hung down about 3.5 inches. It did get lots of inqueries and questions such as "why is your spoiler back there?", etc, so I went back to the stock ones. A neat test is to take many 8 to 10 inch pieces of bright ribbon and tape all over the roof and rear of the car and then drive it with a chase car and video camera so you can see what the air is doing at the rear at different speeds. I think you'll be amazed.