Ok guys, going to update this since version 2 is now done.

I Re-designed the mounting points. At first I had drilled/tapped holes in the frame rails and bolted aluminum L brackets to them. To simplify, make a stronger mounting point, and save weight, I changed the design to a small section of angle iron welded to the frame rail with a weld nut welded to that:

Fabbing the new mounting tabs:



Old tab design, total weight 281 grams:



New tab design, total weight 157 grams:



Tab welded to the frame rail:



Version 1 of the flat bottom, post- Auto Club Speedway. It survived the day, plus hundreds of miles to/from the event on the highway, but it served its purpose as a prototype and now its time to move on to something that won't melt



Version 2, lighter and more rigid, plus almost entirely aluminum, so no melting! Total weight is down around 11.5 lbs! I re-used the rear side sections since they are nowhere near the exhaust, and that way I didn't have to re-make the NACA duct that supplies cool air to the differential:





Just finished mounting version 2, and mating it to the rear diffuser. I'll take a mounted picture tomorrow.

-Ryan

 

Looks fantastic, what thickness is the aluminium and you just rivetted the alloy angle to it?

What did you pay for the sheet, down here in Oz im guessing price will be double but it would be nice to know.

Dann

 

Good job ThePass I too in the future will be changing the design and will do the same as my first one go from side skirt to side skirt, then axle to axle. The reason it will be changing is due to the new engine transplant, I need frame rails.

 

Thanks man. Keeping some of those details to myself.
Aluminum is affordable at my local Industrial Metal Supply ~$3.00 per lb. All the more reason to build things lightweight if you're paying for material by the pound right?

-Ryan

 

Took a couple of mounted pics today while I was working on the car. Pics of the underbody when the car is only ~15" off the ground don't look great, but what-ev. Maybe some time I'll have the car on a lift and be able to snap a good pic:

 

Its good enough for me, I would like to take better pics of mine but I don't have jack points yet.

 

reviving this from the dead to see progress!! That and have you considered adding sheeting out to the sides of the car to create one smooth tunnel? Side skirts that stop air from coming in from the sides would also improve efficiency.

My plan looks a lot like your set up but i think I might run the exhaust out past the license plates to get more air flow into that low pressure zone back there

 

I'm going to be building a flat underbody for my miata within the next few weeks, but I have a few questions before I dive into this whole process.

1) My biggest issue is where and how you guys are mounting the panels? I was thinking of mounting the panel over the outside of the frame rails and then on some of the bracing but some more insight on this particular topic would be much appreciated.
2) I see some people having the entire underside covered while others have a channel for the exhaust. What are the pros/cons to each one? If I decide to cover the entire underside, would I have to bend the panel in order to fit over the exhaust or what?
3) What material are you guys using? I've read that 2mm 5052 aluminum is perfect. Is this the correct thickness/grade aluminum?

I'm sure I'll have some more questions once I dive into the process, but this is all I can think of at them moment.

 

I used .063 t6 6061 and dzus fasteners

 

Nice, so you don't have any issues with the rigidity of the panel?

 

Nothing, I drove it to 128 mph on stock power and I noticed the wind noise was lessen. The car didn't float at high speed, but during street drives mine was noisy during bumps. Driving it at high speeds make you nerves go, not knowing if the wind would break it off.

 

Interesting, as in it rattled or clanked or what?

 

Planning a flat underbody for my turbo. As others I'm concerned about engine, exhaust and tranny heat, and how to shed them. Therefore my idea was to use 3mm ABS plastic with a 1.5mm aluminium center section around the catalytic converter and exhaust. I some spots I'd replace the flat aluminium panels with some louvered aluminium panels to promote airflow through the transmission tunnel and out underneath the car. Have others tried going that route before?

 

I am looking to do another floor also, so here is my idea to correct mine. From the front I will build a front Diffuser like my 1993 did, but with a lot more DF. The floor will be the same .063 T6 Alum, but now with 4-10 NACA ducts. The most important thing is to make sure that there is an escape for the heat in the back. Remember 2/3 of the drag of the car comes from the rear end with the massive amounts of low pressure.