Quote Originally Posted by BipDBo View Post
I theorize that some good aggressive hood louvers would not just be aesthetic, but greatly improve the airflow through the radiator and even add a little bit of down force.
I know that the 818 has been kind of plagued with airflow issues, specifically through the front mounted radiator. The problem is not the intake but rather the outlet. The hood has a decent slope to it and the 818 hood vent is just two very small perforated panels. Because of that slope, that hood is likely more of an aerodynamic high pressure zone, which is normally a good thing for down force, but it turns those perforated openings into ram air intakes. The hood opening fights with the front intake, and the front intake wins, but most of the air leaves sideways through the fenders. Much better airflow through the radiator might be achieved by replacing those perforated panels with sloped louver fins, the bigger the better. It would be best if the first fin protruded from the hood, and each additional fin was shorter, so that the trailing edges were level with each other (see this quick, crude drawing). This will create low pressure just over the opening, and draw air up, away from the radiator.
hood louvers.JPG
If the 818 hood openings are expander to one much larger opening with a large enough louver, the air path out to the sides could be closed off. All of the air can be pushed up, which would increase down force. Two small flex ducts could run from in front of the radiator and blow onto the front brake discs. A louver's "free area" is the area perpendicular to the path of airflow usually about half of the surface area of the louver's frame. The louver's free area would have to have to be as large or larger than the intake, preferably 50% larger. So the outlet louver(s) should be pretty large, a total frame area of 2X to 3X the size of the front intake.
But my theory might not work any better than the current design in practice. The windshield may maintain a high pressure pocket of air above the hood. The only way to know for sure we be to make a crude and ugly prototype that can be field modified and test it out. You don't need a wind tunnel. You could get quantitative measurements by mounting an anemometer or a pitot tube in the airstream, right in front of the radiator and drive it around the track.
I agree with your assessment. The hood louvers for the GTM was the first louver project I did.....and for the same reasons you list. FFR had the GTM hood set up pretty much just like the 818.....some small openings with perforated aluminum. I figured (as you did) that driving down the road, at best the perforated metal was acting as an "air curtain" where the air flowing across the surface was blocking the air under the hood from coming up thru the hood....and at worst, the air was actually trying to flow backwards, and only a difference in more pressure under the hood than above the hood would force the air out.....or find another route.

And yes, I would agree that putting a higher lip at the front of the opening along with a larger opening will create the low pressure area needed to draw the air out from under the hood instead of having to force the air out from under the hood with higher pressure.

Now.....who wants a set of free set of hood louvers in exchange for splashing a crude mould of that area of the hood for me? ;-)