I just wanted to share my experience with sound deadening. I didn't have too much in the expectation department as I was essentially replacing my falling down and disintegrating foam. I pulled the engine cover and cleaned it up. I used the 3m spray contact adhesive. This product has adhesive backing but I wanted to make sure it adhered and it did.
Amazon.com: Noico Green 170 mil 36 sqft Сar Waterproof Sound Insulation, Heat and Cool Liner, Self-Adhesive Closed Cell PE Foam Deadening Material (1/6'' Thick Sound Deadener) : Automotive
After I did this layer I used this
https://www.amazon.com/gp/product/B00069QLVC/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1 I've only done the top section when the hatch is open and haven't done a second layer in the larger area of the hatch. I also sealed with this
https://www.amazon.com/gp/product/B07V2N1N6L/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1 Not the best in the world and some work needs to be done here. Perhaps the pipe insulation is the best choice. I also played around cutting strips of the hood liner material as a seal.
As of now I would say that I've cut the sound in half. I was driving across the lake with my daughter at 9,000 rpms last night and she was sitting on the engine compartment and we were almost at a normal face to face conversation level.
Not as clean as some and I need to clean up some seals but here are a couple of pics.
View attachment 183298View attachment 183299
I'm liking the hood liner, I still have to do mine. If you look back, I installed a false floor with hood lining underneath the board. This made a huge difference. My only concern is in the event of an emergency (fire), access to the engines for the extinguisher will be extremely limited. I'm reconsidering removing the false floor and installing hood liner like you and others have done. I've done the pipe insulation trick and will say that this is the go. Bit tricky to install but it creates a nice tight seal and stops noise pretty well.