I tried myself and it seems to work great. I kept the plastic supporting arms in place and realized it was so strong I didn't need to make provisions for the triangle bar since the grill I used made for some nice added support. Will post up pics on how I did this and how I stiffened up the center section tomorrow when i'm at my other pc. Hopefully it'll help you guys out.
No more floppy/flimsy Seibon CF rear!
EDIT: Here's what I did. Seems to be working out so far. I love that it's noticeably lighter than even the factory 91 valance. It turned out to be a lot more work than I expected but now pretty rigid.
1. Once you open the packaging you will notice it's not a 100% bolt on. For the price, I was ok with this and wanted to line it up myself for the perfect fit anyway. I had to mark exactly where I wanted the mounting holes to be drilled. A long meticulous process.
2. This is where most people stop and think.. there's no place to install the factory mount. Where the factory plastic mounts, I call them "fangs" because they look like fangs, should mount does not exist. I consider this a fail on Seibon's part. This is how it comes...
3. I added 2 more bolt/nuts to better secure the unit and notched it for the fangs. This is what I did.
4. This is where I thought I had to make use of the factory triangle beam. Notice how the center section of the "diffuser" already is depressed/sagging in the middle. When seeing this on other cars I always thought it was the heat from the exhaust but it appears to come this way already. Another fail Seibon... I later realized I did not need the triangle bar because it was plenty rigid.
5. I thought of a rather simple idea to address the sagging center while also adding extra rigidity. I had some left over home depot fire retardant spray foam which I filled the inside with. It's good to past 300degs. This made the "diffuser" super rigid and I was happy with that. I had to buy two kinds because I ran out which explains the two colored foam. I later coated any exposed section with left over bed liner material. It should be good to go for a while. Below was my first attempt. 2nd time was better lol.
6. The fangs don't quite line up.
7. I fabricated some simple brackets which I drilled and tapped for the factory bolt. This was the ticket for the added support. You can sort of see the finished install on pic #5
8. The finishing touch was to add a screen. My version bolts in 8 stealth locations. This ties everything in structurally yet still allows for a little bit of flex.
9. Last was prime and paint. I suck at this and will be taking it to a pro.. probably to LT BMW.
10. I'm pretty happy with the results. This is in "street" trim. I'm considering mounting a proper diffuser when I work on under body aero this next year.
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