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Jaynen UltraDork
5/7/19 12:38 p.m.

I want to put a very simple NASA style flat airdam on my NB track car. Can I just screw it into the bumper? Are screws strong enough? I see some people use rivets, having not used rivets before do you have to predill for them then somehow access both sides of the hole?

How many support rods do I need if its not connecting to a splitter? 1 middle 1 each side?


What support rods do people use?

stafford1500 Dork
5/7/19 1:05 p.m.

Basically the shape of an air dam around the front corners of the car should provide enough support at the outer ends. The center will need some sort of support for high speed activity (higher than highway speeds, assuming the material is at least 1/16" thick). That support can be a thicker piece of air dam material, a flange near the bottom edge (facing back under the car), or braces from the body to the back side (or front side) of the air dam. You would likely need two, roughly spaced at the edges of the radiator inlet on an NB, maybe a little closer to center.

One of the big unknowns in your post is how tall are you going to make this air dam and how much angle you plan to have in is (from the side view). More length means you need more support, more angle provides strength from inherent shape.

Rivets do need to be pre-dilled for the best fit up, but only drill a few holes at a time to make sure the material conforms to the body as you progress from the center around the corners. You should look for rivets that expand a lot when squeezed and use back up washers to help spread the load. Use large flange rivets too, that helps spread the load a bit more on the outside. You can use screws straight into the bumper, but the screws are more likely to pull out since there is only a small area reacting all the load.

Robbie UltimaDork
5/7/19 1:49 p.m.

Use rivets. They are awesome. You will wonder why you never did before. 

Keith Tanner
Keith Tanner MegaDork
5/7/19 2:07 p.m.

Here's what I did on my NA.

Started with the generic Garage Vary airdam. Put a flat panel on the backside.

There are rivnuts in the panel, and screws go through the airdam to fasten them together. Rivnuts > rivets.

A second piece of aluminum attaches to the bottom of that and protrudes 3" from the front of the airdam. It's screwed in to those same rivnuts plus a line of them across the trailing edge of the splitter panel. Two cables support the front edge of the splitter. The top of the cables are attached to the radiator support visible when you pop the hood.

I also added wheel spats and a small L bracket to hook it to the ends of the splitter. Again, attached with screws and rivnuts. The spats are very strong, mostly because of what I had kicking around.

Canards were also added later, which helped front grip nicely. They're riveted to the body and attached with screws and rivnuts to the airdam. The canards are very thin metal, they're not structural for the airdam at all.

I can pull this airdam pretty easily using nothing more than a screwdriver, which helps with loading the trailer nicely. The spats and canards stay in place.

Here's the result crossing the start/finish at Laguna Seca, so it's got a fair aerodynamic load going with no significant deflection.

Jaynen UltraDork
5/7/19 5:13 p.m.

I am just planning a flat dam like this, I already have the LRB Speed undertray which terminates at the bottom of the bumper, the flat airdam is cheaper even than buying a GV knockoff lip at least new and seemed better than just using stock bumper? So I want to add something to the front of the car to work in concert with the undertray to offset a lexan spoiler. I have a new bumper skin for my car that is currently off the car if that would be the easiest way to mount the airdam and then mount it to the car. I have yet to take the old one off.

There are holes in the upper portion of my current bumper skin or I would have left it be

Jaynen UltraDork
5/7/19 5:14 p.m.

Is there a clever way maybe to make the bumper skin easily removable and that would then allow the dam to come off in case it causes issues when loading on the trailer?

Keith Tanner
Keith Tanner MegaDork
5/7/19 5:35 p.m.

Duh, airdam and not splitter. I'd go check to see what the Supermiata guys are doing, as this is their standard setup. I think most of them have a removeable front because it would pretty much be required for a trailer load.

Mine is the result of two things: the way the car evolved and the fact that I think the Supermiata option is ugly. Effective, but ugly. My nose is slightly draggier than the flat one assuming they're both running a splitter. 

A lot of guys will build a structure behind the bumper that makes the splitter strong enough to stand on. This is impressive but kind of redundant because you'll never get a 150+ lb point load on the splitter.

Jaynen UltraDork
5/7/19 6:40 p.m.

I am afraid that most of the supermiata threads as much as I respect those guys are not very friendly to asking stupid questions, the answer is kind of go figure it out on your own which I was hoping to get some insight before doing :P

DaveEstey PowerDork
5/9/19 9:06 a.m.

I've not yet begun attaching aero to the front of my RX7, but I've built a new front "bumper" support with it in mind. Your mileage may vary - I don't recall what the front bumper supports looked like when I owned my Miatas.

Rodan HalfDork
5/14/19 8:15 p.m.

The basic Supermiata format uses a birch splitter, with landscaping trim for the lower air dam support.

Landscaping edging

You can design the splitter so it ends flush with the airdam, or have it extend further forward.  You want the splitter so you can control the airflow through your radiator.

Understand you will need some rear aero to balance out the changes up front, even with no splitter sticking out from the air dam.  The more the splitter protrudes, the more rear aero you will need.

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