I have my intake for the air box on one side and a duct for the rotrex oil cooler on the other. I see lots of data for hood vents etc but none (that I found) discuss that area of the car.

 

I believe they are. Based on the amount of shredded bug guts that end up behind a set of screened IL motorsports open turn signals I had they work pretty good as inlets.

The head light lids aren't but I do believe a properly shaped NACA duct in the headlight lid will overcome that.

Currently I put the turn signal lights back in for better aero and am using a NACA headlight lid for engine intake.

Bob

 

Rise, O necrothread.

Been doing some pondering, and some searching. Lots of threads with info, but a lot of them are old, and as such, many of the pics in them are no longer available due to hosting issues. From what I gather, on an OEM NA body, the turn signal area is medium-high pressure. However, the headlight cover area just aft of there seems to be low (would it be called negative?) pressure. See top left pic:



It seems to me that turn signal intakes would do something (unsure how much) to get air into the engine compartment. However, I've also seen headlight covers with intakes, such as these:




Now, maybe the ducts generate some flow of cooler air into the openings from aerodynamic forces, but it seems like a lot of potential would be countered by the low pressure zone there sucking air out.

I'm thinking to do something similar to the louvered cover, above, except with the louvers facing the other direction, i.e. with the openings towards the aft. I think it would work better to enhance airflow through the engine compartment. The low pressure should help pull air out, without the aerodynamics trying to push air in. Obviously, vents or louvers on the hood would be more effective, simply because there's more surface area to work with, but it also takes a bigger commitment towards fabrication (due to the hood substructure) and practicality/streetability. I don't have that kind of commitment yet.

Thoughts on the theory, or am I just going the wrong direction entirely?

 

Your headlights aren't really an ideal location to pull air from your radiator.

If better cooling is your goal, I'd look into hood louvers or don't bother.

 

naca duct lid is boss. boss people do it.

 

Oh god, we're not going to start at square one again with this are we?

 

NACA duct shapes seem to have the ability to suck air in from surfaces with less than optimal pressure differentials as long as there is fairly steady flow over them. They also tend to do it with much lower overall drag than a scoop like duct because they don't rely on stagnation pressure generating pressure differential to force flow through an opening rather they create a vortex that creates momentum in the direction to feed the opening.

Without a proper NACA shape I think the headlight lid becomes an outlet rather than an inlet.

 

The lids are outlets. Relying on them to draw area from the back of the radiator is not something I'd try, unless you've gone through the trouble of perfectly sealing the engine bay forward of the radiator. My suspicion is that you will draw air from places that aren't the back of the radiator.

 

couldn't you just tape some twine around the opening, mount up that GoPro, and find out what is going on?

 

I did that like 7 years ago. But no longer have the video. all string was sucked into the opening.

my intake was DIRECTLY behind the opening and was boxed in from the engine bay.

I used to have a great pic, but this is best i can find:

 

I have a home made NACA lid with my intake directly behind it it a box like structure. Its not perfectly seald from the engine compartment but not bad. definately heat shielded from the turbo. String tuft testing way back when I did it showed air going in it.

I ditched the turn signal intakes for reduced drag and I they were cirtainly detramental to engine cooling.

 

The picture of the red headlight cover above with the nice carbon NACA duct might be misleading.

I have never seen one like that available, with square edges, long (proper) length to the duct itself etc.

Mine and any others I have seen have a short "approximation" of a NACA duct which is likely significantly less effective. From my research the square edges are a critical part of the design as is the length to width ratio.

I have been running my intake from down in front of the wheel in a sealed area but in the interests of shortening the intake tract am going back to the behind the headlight method in an effort to drop lower my spooling as best i can...due to big turbo, small engine etc.

As such I would love to know where to get one of these more realistic looking headlight cover NACA ducts!

 

 

Okay smarty pants

looks great, where do these come from?

 

the NACA duct is sourced from McKinney. Looks like he glassed it to the headlight lid, you can see where he cut the NACA shape out of it. As seen on revlimiter.net

revlimiter.net - NACA duct intake install

 

exactly that.

 

Slick Auto used to make a NACA lid which FM sold.

 

So...are y'all saying using a NACA ducted lid as an inlet would be better than using a reverse-louvered lid as an outlet? I guess I can see Andrew's point about not drawing air from the radiator, since the louvers would basically be even with the radiator.

 

what would the lid outlet?

that would only make sense if you did remove the turn signal, and put your filter where the headlight resides, then sealed it off completely. so air would flow through the opening and out the lid through the louvers.

otherwise they will only really do anything when youre parked...might as well do hood lifters while youre at it.

 

The rear of the headlight doors is a low pressure area and would be a good place to vent pressure from under the hood according to the pressure charts posted on this forum. It is also rear of the radiator (not that it matters because the air flows in many directions beneath the hood).