Engine bay pressure?
 

One thing that has prevented me from doing my underbody panel for 2 years is where does the air go that cools the radiator?
I am sure you guys read these 4 year old articles by now, but i couldn't find them discussed here:
Part 1 Testing Pressures
AutoSpeed Part1

air enters the grille opening to cool radiator
http://us1.webpublications.com.au/st...1/2159_5lo.jpg

but if we seal off under the engine, where can the air go?
http://us1.webpublications.com.au/st...1/2159_6lo.jpg

stock it leaves underneath
http://us1.webpublications.com.au/st...1/2159_3lo.jpg

if we seal underneath, we should allow some venting, and ideally vent the front of the hood
http://us1.webpublications.com.au/st...1/2159_2lo.jpg


but i am no way going to cut into my hood!

Part 2 Making an undertray
AutoSpeed Part2

Part 3 Helping air escape
AutoSpeed Part3


So no one has overheating problems sealing everything off? I understand this article is saying that once air enters to cool the radiator, without an exit, pressure is so high, no more air will enter.

To me we should have a vent somewhere on the undertray, located probably towards the front, maybe behind an AIR DAM, for engine air to escape???

i think i read someone has air come out into their wheel wells since it is already turbulent? so cut into the fenders' interior???

Another piece of knowledge from the racing community: Make a sealed duct-work from the nose to the rad to the wheel well. Make it completely sealed all the way around the rad, and sealed around the entrance and exit. This way ALL air entering the front hits the rad for best cooling and exits in the wheel well. You can have an air-tight engine bay.

sealing
 

They'd have BIG problems if the bay were sealed.Short of cutting onto the hood,you'll have to use the front wheel wells or under engine bay area for air to escape.Exits at low pressure areas are best,but thats at the high camber area of the nose,and at the A-pillars.Both require hood penetrations.

that seems like A LOT of work. would that require removing the fans? i can't even imagine having enough space to add the ductwork. I think there may be someone on this forum that is will to try it seeing the tremendous benefits.


so it would be okay to have no airflow over the engine bay componenet? cooling the rad to circulate coolant is enough? my stock setup tries to seal the incoming air at the main grille into the radiator with side fins and closing the top. but the rad extends down to below the actual bumper.

i was planning to add coroplast to keep the air from slamming down to the undertray. but thinking of pressure, unless totally sealed ducting like you mentioned, it will find it's way down there anyway.

I'm thinking just open vents into the wells and a vent behind an air dam below.

i just looked at my old OEM undertray. I couldnt reattach it when i changed to a larger bumper. It seems it's main purpose was to seal the radiator. the rubber side fins extend to the bottom of my rad. this oem tray covered just beyond the bottom with a foam strip lining the rad. it also had an AIR DAM close to the front. but my new bumper extends a few inches outward and lower than the oem air dam.

the removal of this piece is what got me started into adding a custom tray. my tray will only go back 7 more inches, so i don't think i have to worry about my engine pressure.

engine bay
 

I did a complete aero-mod installment for internal drag.You might want to track it down and take a look.If you do a complete racing style cooling system (if you could!) it would be good for a 12% drag reduction and about 6% improvement in mpg.You can way the cost/benefit.

Yes it will be somewhat difficult to fit the ducting in there, however, you don't need the ducts to be as large as the rad the whole way. Think of the ducting for your airbox. You have a small tube that leads to a box with a big square filter in it and then another small tube out.

That's what you want to do with your rad. Have a small opening in the high pressure front of the car, have the ducting open up to the front of the rad, then behind the rad (and fan, which stays in place attached to the rad) you go back down to smaller piping and exit in the wheel well.

ok that makes perfect sense.

seeing how my rad is sealed off in the front, (except the bottom, but will be when i make my tray) how do i determine if i should block my lower grille?


air will enter the top grille and go down to behind the lower grille anyway. if i block it, i still have a pocket since the lower grille opening is recessed. will it be an advantage to having a pocket closed off down there, or the air hitting the lower radiator?

and if it's blocked off, there seems to be a sensor located there. i wonder if that will affect anything?

That looks tricky. Does that car have a HUGE rad, or is it just the way it looks? There seems to be lots of open space in there to grab air and slow you down... without hands on the car, i really couldn't give you more than the theory. GOOD LUCK! (I'm such a cop-out)

my rad is HUGE. it starts at the very top of the top grille to where you see it below. it's as wide as the headlights. i guess i can relocate the sensor to up top.

i see 2 options. not sure which would be better.