Found this cool xls that let's you "tune" your DIY NACA duct to proper dimensions:

http://sports.racer.net/tech_info/ae...calculator.xls

 

Excellent tool, thank you very much. It's funny cause I was just talking about making a custom NACA duct for my coworkers 24 Hours of Lemons car since they're planning on relocating the radiator to the trunk.

 

too late.

 

Do you have to make your own. Or can you buy one somewhere. I've seen one on Moss but it was stupid high.
I'll build one before I pay that.

 

From all the pages I read about NACA ducts, the pre-made ones are all made incorrectly (sharp edges should be used). However, when can one utilize a NACA duct unless you're like 100+ mph?

I think you'd probably have the same effect of a NACA duct by just cutting a hole into the headlight. But who knows, it couldn't hurt and it looks pretty shweet.

 

The other problem they all have is that the ramp angle is way too high, causing the air to tend to separate rather than stay attached and flow down into the duct. Also, having any kind of step or bump to trigger turbulence or separation as the air enters the ramp will destroy duct efficiency.

All the pre-made ducts I could find looked worse than useless. I Googled and found the original declassified NACA paper. Used the general guidelines and dimension sets there to build a spreadsheet to calculate coordinates to lay out a duct based on a few parameters. Probably basically what's on the link provided above.