Roof flex

[Swordlordboy1234]

So 120 sq feet of 60mil deadener (200% coverage) and approx 30-40sq feet of that is already on my roof. The issue I'm having is the flex below my resonate freq of 34hz. My f3 to the ear is about 25. But 26-32hz my car begins to shake violently. The worst between 26 and 28. The rear door flex and the roof flex is between 1/2inch and 1 full inch depending on the locations. Sunroof itself moves about 2inches total.

I'm considering foaming between the metal/deadener on my roof and the vinyl headliner. I can't use wood or fabrication because that will break me out of stock USACI class. But I feel like my lows are suffering because of the flex. The doors I plan to put about 10lbs more (yes 10 lbs) per door of deadener to try to weigh it down more to stop some flex. The rear doors just get annoying. And so I'm just stuck with the issue of the roof.

I think if I have the sunroof (headliner) cover still able to slide back and forth, while having a solid roof and headliner overall will be considered a success. Yes it needs it. Today I was holding my hand on the inside of the roof pushing up on it as hard as I could and it was still flexing violently about 1/4 inch. Over a half inch when I'm not pushing on it. But I feel like the flex is where I'm losing all of my DBs.

Does anyone have any suggestions before I go foaming more parts of my car? I already have the back of the headliner (to hold it up) foamed and it happens to be solid as a rock, along with foaming the seal off of the box combined with my crazy amounts of deadener my rear deck is solid as a rock. So unless someone can give me other options I believe this is a good solution to my issue.

Thoughts?

[hdorre]

Just do what Kevin did.. Cut your roof, and replace it with resin and sand

/trolling

Im in a similar boat, and get roof flex. Maybe not as much as you (partially bc of sunroof), but some.. If I competed, Id probably fill the voids with expanding foam. Before you do that though, is there some sort of particle board on the reverse side of your headliner?

Also, where do you seem to flex the most? By the sunroof?

Sorry if its been answered, Im half asleep..

[Swordlordboy1234]

The most flex is closer to the sunroof but the whole roof is pretty violent IMO.

I'm at a point where I can either take down 3/4 of the headliner and foam parts that I can (which I don't wanna do) and then foam the middle.

Or I can leave it where it is and foam it from the middle (there is a small hole right behind the sunroof) I could spray in a 360 and most likely not effect any moving parts of the sunroof or my headliner.. Though any future headliner / wires up there will be a pain in the ass to get to. But none of the interior lights work anyways.

Yes the vinyl on the headliner has some kind of thick particle board attached with some form of pillow like foam as "sound deadener" but apparently 4k of power on a BHE box makes that stock stuff flex too much.

I'm 99% sure I won't mess with any drains as long as I don't spray into the actual sunroof mechanism but any headliner area is open hunting if memory serves me correctly.

[SavantStrike]

I'm not familiar with the classes.

Just what can you get away with before it's considered "fabrication?"

I know it would be a pain, but what if you replaced the particle board in the headliner with something beefier like say, plywood? You could do ultra thin plywood and it would be comparable to the stock particle board (thickness wise) but a heck of a lot stronger.