Integrated Air Dam/Engine Undertray/Bellypan
 

Hello all! I am back with a 1994 Geo Metro 5-door. So far it's stock and I'm getting great results just using hypermiling techniques. But I can never leave anything alone.

I've had this idea bouncing around in my brain for several years now, and I finally have the car to try it on. It is an air dam with a flat bottom that goes under the engine (like modern VW's). This is several inches lower than the bellypan. The airflow goes through the radiator, follows the undertray, and comes out and merges with the air flowing under the car.

It would have a grille block and wheel spats and all that. But I was wanting a way to extract high pressure engine compartment air and maintain some radiator flow, while keeping everything flowing as smoothly as possible (because isn't that the whole point of a grille block, to stop air from getting muddied up in the engine compartment and exiting to the "dirty" underside of the car?)

What do you guys think? I've got my 4x8 sheet of Coroplast and am going to start working on this soon.

lower
 

I'd be disinclined towards having the bottom lower than the belly of the Metro.You'll be introducing a backwards facing step,much like the bed of a pickup truck under the car with a horrific flow discontinuity and major perturbation as the fields attempt to mix.
I'd recommend that you look at what Ferrari is doing.They're spending hundreds of thousands of Euros in the wind tunnel to design efficient pans and extractors.

A very quick search of Ferrari aero on Google yielded some interesting ideas. Do you have any other sources for what they are doing?

So instead of making a step, have more of a NACA duct or ducts to extract cooling air from behind the radiator?

sources
 

The belly of one of Ferrari's cars made the cover photo of AutoWeek years ago.
Some other rags have covered iterations on their development work.
The 599 XX car had a complete underside image in one article.
I'd have to dig around.
Dr. Alberto Morelli did exhaustive research for the air extractors on the CNR 'banana' car of 1976-78.You'll find images of this car online.It's here at EcoModder too but 'don't know where.Sorry!
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The idea is to have the air exit and blend at the same local velocity as the source coming at it so it neither creates a vacuum nor jet which would trigger turbulence.
This would be tough without a full-scale wind tunnel.
If you're near a municipal airport and have access to the flightline,you might be able to inspect some engine cowlings on Cessna,Piper,and BeechCraft,etc..
These will be 'engineered' designs.
Ask for permission before you go walking around out there.;)