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240z Urethane Air Dam Modification/Splitter


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Ever since I saw a photo of my car on the freeway with the air dam pushed in because

of the wind, I've been trying to reinforce the urethane air dam. I'm not sure if all

urethane air dams have this problem, or if later version of this air dam are more rigid.




I first tried to simply attach some aluminum brackets on the radiator support to keep

the air dam pushed forward. Although it was a solution, there was still room for

improvement. The inside of the air dam, along the bottom edge of the front lip, runs

a 3/8 extension. I ended up riveting some tabs onto this extension to be able to bolt

on an aluminum plate I had previously mounted with hanging brackets.


(old version)





(new version)






(I ended up attaching another one of those brackets on the right side, to hold up

the plate.)


With the tabs riveted to the air damn, the plate and the air dam can be removed in one

piece, and when bolted onto the car, it's extremely rigid. Going one step further...I got

a hold of some ABS plastic to make a little lip extension. I thought I'd might as well since

there was something to attach it to now. After a few days though, I didn't take into account

the heat of the sun, which was making the plastic sheet expand (probably should have got a

thicker sheet), distorting the lip. But that's nothing a little fiberglass can't fix. With 2

layers of mat around the border, the 1/8 inch thick abs is now close to 1/4 inch.









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  • 2 weeks later...

When I installed my airdam I left the lower grill on behind it (280z). This gives the dam something to rest against when the wind is pushing on it. I did a track day at 100 degree temps (airdam was soft), and didn't notice any deflection in the pics at 100mph.


of course from an air management point of view, your modification is far better.

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  • 4 weeks later...
  • 6 months later...

There are lots of cored products that might be good for this too. I have seen some thin aluminum sheets (~.040") bonded to foam core used for making signs. It's tough, light and very rigid. Not sure how thin you can get it, but I bet you could buy a piece from a local sign shop.


Some of these look like what I saw...My link

Edited by Snailed
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  • 1 year later...

I just did this mod... used 3/16th abs sheet... cost about 46 bucks at TAP Plastics to get cut in 17x60. I used a plastic 2.5 inch disc with a hole in the middle and ran it around the outside of the lip on cardboard to make the template. I also used some 2'' wide aluminum about the same thickness to bracket it up in the middle, going straight down from the horn mounts. Took a lot longer than I expected and isn't the easiest to do, especially getting the edges right.



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The hotter it gets, and if you're in the Desert SW that means any time it's over 85 when the sky is clear.... the urethane dams get really flexy.


One alternative is to make a reinforcement 'skeleton' behind the lower part of the lip using 1/4 or slightly larger metal rod. Trick is to not make it TOO rigid! A simple loop will do to keep the lower portion from folding under. It allows you to dink a parking lot barrier and still bend. Yeah, you got to now straighten the rod because it doesn't bounce back like the urethane does... but it's pretty quick and easy to make.


just another thought. I like the splitter-look done here as well.


Oh, and for you guys in SoCal looking for ANYTHING plastic, check out S&W Plastics (they are in the book, on the web as well I believe) Anything from ABS, Perspex, Polycarbonate, you name it they either have it in stock or can get it for you!

Edited by Tony D
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The coefficient of thermal expansion is very high for most plastics, especially un-reinforced, compared to other materials. Slotted or oversize holes to allow the plastic piece to move independently is the common way to attach large pieces, to reduce warping in hot environments.


This is overkill, but here's an example from a materials supplier, Page 26 - http://plastics.dupont.com/plastics/pdflit/americas/general/H76838.pdf


Here's another reference - http://www.engineeringtoolbox.com/linear-expansion-coefficients-d_95.html


Just a few odd facts to twist up your day...

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