Custom cold air NACA duct project
 

So, I came upon this carbon fiber/fiberglass hood on craigslist, $100 picked up. I thought it wasn't a bad deal, and heck, it actually fits very good. But what I really wanted was to modify in a duct to draw cold air into the airbox. I have seen some other mods for this, but I had a vision of this ducting and so it began...

This is an actual pic of the hood with my final renderings of the duct and vents on there.
http://i279.photobucket.com/albums/k...odsketch21.jpg

Then, I laid out my design on the hood itself.
http://i279.photobucket.com/albums/k...7/DSC00391.jpg

http://i279.photobucket.com/albums/k...7/DSC00395.jpg

From the back, you can see where the duct pokes thru, but to align with the inlet it will need a "box" built up around it with a hole in the bottom to meet up with the inlet.
http://i279.photobucket.com/albums/k...omwithduct.jpg

This is the inlet tract on the stock airbox with the stock ducting removed. It feeds air below the flat panel K&N.
http://i279.photobucket.com/albums/k...7/DSC00490.jpg

And I cut...
http://i279.photobucket.com/albums/k...7/DSC00397.jpg

Initially, I had planned for the duct to swoop right into the inlet, but after some changes this would not be feasible. However, I did make that duct, here is the plug I started from foam. It was eventually covered with filler, sanded, glassed, and subsequently thrown away.
http://i279.photobucket.com/albums/k...7/DSC00404.jpg

What I ended up doing to make the duct was to stretch nylon (pantyhose) over the bottom of the cutout (no pic). Then, I fixed a rectangle shaped piece of cardboard at the back of the duct with the nylon stretched over top. I wet that out with poly resin and let harden.
http://i279.photobucket.com/albums/k...7/DSC01800.jpg

Then I layed it up with a few layers of fiberglass CSM.
http://i279.photobucket.com/albums/k...7/DSC00494.jpg

Here is a view from the top side of the hood...
http://i279.photobucket.com/albums/k...7/DSC00495.jpg

http://i279.photobucket.com/albums/k...7/DSC00498.jpg

Very neat project! Looks like some decent fab work as well. I am curious about why you have chosen to duct from that location instead of pursuing a intake air path lower to the ground?

yes, it looks like some very good and fairly intuitive work - scratch that - it IS very good work! however, i was sort of wondering why you didn't choose a different path as well.

Ok, for the inlet duct, I had to make a sleeve that would fit over the stock opening and connect to the duct.

First I made a mold of the shape of the inlet. Then I wrapped it in tape and then aluminum tape for a release agent (no pic).
http://i279.photobucket.com/albums/k...7/DSC00484.jpg

http://i279.photobucket.com/albums/k...7/DSC00486.jpg

http://i279.photobucket.com/albums/k...7/DSC00485.jpg

Then I simply layed up the CSM around the plug building up about an 1/8" of fiberglass, or 4 layers of 1.5oz CSM. I used a sharpie to mark the plug inside for cutting guide later.
http://i279.photobucket.com/albums/k...7/DSC01802.jpg

http://i279.photobucket.com/albums/k...7/DSC01805.jpg

I pulled out the plug, it came out in one piece, surprisingly, could reuse if need be. The "loop" of fiberglass that remained is very strong.
http://i279.photobucket.com/albums/k...7/DSC00487.jpg

http://i279.photobucket.com/albums/k...7/DSC00488.jpg

http://i279.photobucket.com/albums/k...7/DSC00489.jpg

Fortunately, the collar fits perfectly!
http://i279.photobucket.com/albums/k...7/DSC00492.jpg

http://i279.photobucket.com/albums/k...7/DSC00493.jpg

Now I'm at the point where I will fab up a "box" stuck to the underside of the hood fed by the NACA duct. The bottom of this box have a cutout aligned with the new extension on the inlet of the airbox. When the hood closes, the two will align and be sealed by weatherstripping.

More pics to come as this project wraps up!

wow nice work.

Thanks, guys! I was initially going to duct straight into the flat panel on the front of the top of the airbox. However, this would have required using conical filter elements and a host of other mods because the panel filter would have been below the opening. In the end, this is similar to how muscle cars use cowl induction hoods to feed cold air to the carb, and I thought some of those design elements would work well here, too.

P.S. The large cutouts in the middle of the hood sit directly over the intercooler. They will be covered with powdercoated hex perf metal and hopefully the exit of the intercooler can be directly ducted to them.

This would be good for the fabrication forum.

what did you use to cut the hood?

good work!

+1 inquiring minds would like to know

I've been thinking about something very, very similar to this.

I made the rough cuts using a Dremel with a reinforced cutoff wheel, and then I went back and cleaned it up with a sanding drum bit and then sanded by hand.

this looks very promising!!! very nice work

This looks very good! I like how clean the design is. Great work! Keep the pics coming I am interested to see what this looks like when it is all finished.

Great work. Keep us posted through the process!!

sweet job man! what does NACA mean btw?

National Advisory Committee for Aeronautics

The predecessor to NASA.

Im keen to see air temprature results, take some temprature checks maybe with and without the duct sealed. I was gonna do exactly the same thing but im gonna go a letterbox in the front bumper and make a tube exactly the same to the air filters.

Nice work!

Did you use the NACA duct calculator ( http://sports.racer.net/tech_info/ae...calculator.xls ), or a pre-formed NACA duct from a race shop ?

:-) neil

Thanks, guys and token girls! I didn't use that calculator, but I used info from this page to calculate the width/height/angle ratios of the duct. I pulled it off the hood to finish it, more pics to come soon...

I made the plug for the box last night, I used aluminum tape for the release agent. It doesn't need to be pretty, and aluminum is an easy, efficient answer. Also, CA glue ftw!

http://i279.photobucket.com/albums/k...7/DSC01818.jpg

The impression of an "arch" seen in the aluminum is where that edge of the box straddles the curvature of the bottom of the duct.
http://i279.photobucket.com/albums/k...7/DSC01820.jpg

The back of the box and top are flat.
http://i279.photobucket.com/albums/k...7/DSC01822.jpg

After this is layed up and cured, I will fit this and the duct to the hood for realz...

Do you have a general idea of your IATs? Power? Anything like that so we can compare before and after on something other than the butt dyno?

nice job dude i cant wait to see what this looks like on your car. keep up the good work :biggrin: