Rear Diffuser

[Sebnuts]

Need some help with a rear diffuser design (I have zero aero knowledge).
I made the bottom of my subframe flush with the bottom of the chassis, so enclosing the bottom of that will be pretty straight forward.
I'm thinking riv nuts in the stock rear floor pans to bolt up the leading edge, and then drilling the subframe and using these automotive push clips to retain the rest of it.

Would these be sufficient, or are the forces high enough that everything should be riv nutted and bolted?
I drew up a thing that kind of looks like a Lotus Elise diffuser.

I'm thinking match the DF floor pan material thickness for the main piece and using 1/8" aluminum for the side pieces. These 3 pieces would be riveted together.
I went a little thicker on the side pieces because they're kind of hanging out in the middle of nowhere. Thinking maybe some little struts or cables might be needed to strengthen further?

Any comments/suggestions for improvements would be greatly appreciated.

 

[Rttoys]

I bolted mine on, but rivnuts will work fine. we just followed the lines of the rear subframe and added some fins, which are bolted on. It could use some refining, but it works. Not sure on the benefits, but it kind of finishes the back end.

 

[Desert Sasqwatch]

IMO, the edges of the aluminum will wear at the plastic fasteners pretty quickly if there is any movement (inevitable). Rivnuts are probably the best choice to keep things in place and nor have worry about anything coming apart at an inopertune time. Just saying...

 

[Rttoys]

To clarify, here’s where mine is bolted to the frame

 

[MX184]

Wish I had a better picture of it at the moment. But I went the rivnut route into the subframe. So far its survived a drag and drive in the carolinas, and a track day at notoriously rough Sebring.

 

[Davidljones88]

I bolted mine on, but rivnuts will work fine. we just followed the lines of the rear subframe and added some fins, which are bolted on. It could use some refining, but it works. Not sure on the benefits, but it kind of finishes the back end.
View attachment 41765
View attachment 41766

How did the car handle after the diffuser?

 

[Rttoys]

Same. Butt accelerometer felt no difference between defuser and no defuser. Aesthetically it looks a lot better than without.

 

[Markm]

I worked on a cobalt when I was still at the dealership that had a factory splash shield and made a terrible noise at highway speed. This particular cobalt was the only one I remember seeing a splash shield on. I wonder how that would do on the rear of the Goblin if you could find one

 

[duthehustle93]

is the entire bottom of your car already flat bellied? if not, you'll definitely want to make sure it is for a diffuser to be additive. Tube frame cars are extremely tricky in terms of aero since you don't really have laminar flow anywhere, and diffusers are also tricky. Diffusers can have a few roles.... they help increase air velocity under your flat bottom/splitter, can mutually benefit with the presence of the vacuum bubble behind the rear bumper (which goblins might not have?), and depending on your resources/data they can positively interact with a rear wing. With that said, they typically work best when paired with bodies that are aerodynamic. It certainly couldn't hurt, but it'd be tricky to see measurable gains. Your CP will probably be somewhere near the center-rear of the flatbelly, so the rear of your diffuser shouldn't be seeing a lot of force, but I would highly recommend not using the push clips... rivnuts would probably be best.