Bottom Cooling...but a little different?
 

I converted my Saturn to 100% bottom cooling via addition of a factory air dam and duct taping up the front opening. I know Corvettes and F-bodies have used 100% bottom cooling in the past as well. I'm beginning to consider this for my current DD, Focus wagon but have a question.

Does the air dam HAVE to be placed directly under the radiator?

My Focus has a panel that is smooth under the front of the car with a small (~3/4 - 1") air dam that drops rearward and doubles as tire spats. The panel attaches to the core support and the dam is rearward of the radiator/core support. I'm thinking about completely blocking my lower grill, adding some length to the current, stock, air dam, and cut some rectangle holes in the panel to allow air up and across the radiator. I'm wondering if the dam NEEDS to be directly under the radiator or if it will have the same results placed behind the radiator but with the "only" place for the air to go being just in front of the radiator?

I can't find any pics of the stock panel but will take pics tomorrow of my car if I can get a good one.

Thanks,

Depending on the application it may not need to be directly under the radiator, but when ot is it maximizes high pressure in front and low pressure behind.

Found a pic on a ebay piece.

6S4Z8327A FO1228106 Front Lower Engine Splash Shield New Ford Focus 2006 | eBay

So the dam could easily be extended with some lawn edging but the "cooling holes" would have to be cut basically where the white sticker is placed. The holes just rearward of the sticker are where the panel attaches to the bottom of the core support.

placed
 

From what I remember,the air dam was directly below the opening of the inlet duct,creating the stagnation pressure to induce the flow in the absence of a scoop (which wouldn't survive in such a location).
The bottom of the airdam on the bottom-breather Trans Am Firebird was around 10mm lower than on the entry level Firebird.
Also,you may not want any type of airdam ahead of your inlet,and you'll want some radius under the bottom edge to keep the flow attached to the inlet,or you might starve the inlet.
I've seen a lot of these on Corvettes and Trans Am's ripped away on driveway ramps.
Watch your clearances!

Thanks Aero, but I think you misunderstood. I'm looking to have my dam farther BACK from the inlet. So there would be a gap of a few inches between the inlet and the dam; the dam would not be directly at the rear of the inlet. Will the dam still create cooling flow in this set-up or does it HAVE to be right behind the inlet?

http://image.corvettefever.com/f/175...l_testing+.jpg
i imagine the pressure created by the air dam wouldn't extend farther forward than something similar to where the smoke bends to go around these lights. making me think that setting an air dam set back at all, will quickly diminish its affect. going more than an inch or so back may pretty much neuter the affect of the pressure in front of the air dam.
in the event that you don't get enough flow, reopening the grill to try to get enough air might even result some air flowing out through the holes, rather than through the radiator. as it sits, it sounds like you have a good front pan up to the radiator to work with, and you could just run a normal grill block. i might not of made mine a bottom breather, but the factory ducting just behind my bumper was already fubar. the differences might come out in the wash, but a bottom breather limits you from a more aggressive air dam at the very front of the car.

Having the air dam would create a region of positive pressure in front of it. On my old car I drew cooling air from the lowest point, but that was the very bottom of the existing bumper which had a splitter like element. If you could incorporate a splitter type element to your air dam I believe it would increase the pressure in that region. Note that this is all based on my limited interpretation of drawings/text in Hucho's book.

Part of what I did to make mine work on my old car was to direct the pressurized air to the radiator in a semi-sealed up duct. Stock, there were many ways that the air could enter the bumper but go around the radiator. I don't know how your car is in this regard, but if you are collecting this air I would want to direct 90+% of it right to where it was needed.

I need to look at mine from underneath to check on all this stuff. Its been a little while since I've been under there and I wasn't looking with a critical eye then. If the pressure isn't enough, do you think fences on each side of the opening, continuing rearward to connect with the dam would help to "push" the pressure farther forward and up into the "cooling chamber"?

Maybe I just need an extra dam right behind the inlet and stop overthinking things...

air dam location
 

*without a NACA submerged inlet,or a Bauman scoop protruding below the boundary layer,there's no reason for the air to rise up into your radiator duct.
*GM positioned their air dams directly below the inlet and tilted them such to produce an auxiliary forward stagnation point,plus provide a deflection of the flow up into the duct.
*If you move the dam too far rearward you can lose all the pressure it creates.
*The dam will produce a low pressure behind itself and if this region is communicated to the rear of the radiator it will assist in the flow.
*If you add capping plates forward of the airdam,to move the positive pressure forwards you will create a parachute.

Perfect :).
So air dam behind the radiator is probably not a good idea and not even worth cutting up my splash shield to test. I'll stick with ram air cooling unless I can come up with an air dam that mounts to the car in conjunction with the shield directly behind the inlet.