As shown at the top of photo my rx7 had roof insulation from factory, it has since been removed and lost. Is it necessary? Can I use anything else?

 

You can use anything else. Any sound or heat absorption mat will work.

 

DEI has some products for that: https://www.designengineering.com/where-to-use/

So do other vendors that sell sound deadening material.


Why is your interior completely gutted?! Mine is similar right now. Doing carpet and sound deadening soon.

 

Awesome thanks for the recommendation! Will look into them and see what I find
car was stripped for a color change is now sunburst yellow , is sound deading needed? I've never once driven the car so unsure on how load road noise is

 

It depends on what you are looking for in the car. The cars were built with minimum insulations and sound absorption to keep them light. I would highly recommend sound and heat absorption if you are street driving the car.

 

the car will be street driven so I think ill look into more sound deadening, is there common areas i should be putting it? There's no doubt a thread on this somwhere

 

Most of the old threads on the topic are actually misguided in retrospect. The old threads here and on other forums had people covering every square inch of the interior in dynamat or similar stuff. That is wrong. You place a small bit of dynamat like stuff on large panels (like doors and roof and a few spots on the floor board to decrease resonance. Then you layer on some other material whose name I forget. It is a multi layer thing to get heat and sound "deadening". Google or use your favorite chat ai or go to the vendor's websites that make this stuff and educate yourself about the multi layer pros/cons.

 

I don't know if I would classify using too much Dynamat (et al) as "wrong" as much as your first descriptor -- "misguided". At least if supreme sound deadening at all costs and winning sound competitions is not your goal.

With sound deadening, there's a very sharp decreasing return. A small amount in the center of a large panel will stop the vast majority of the resonance. And while more is objectively "better", it may not be worth the trade-off in cost and certainly, in a vehicle like ours, in weight. Sound deadening is both expensive and quite heavy. Not when used conservatively, but it can get really out-of-hand real quick. You could (and I've seen some people do it) add more than 250lbs of sound deadening products real easy without even really realizing it.

There's no singular answer on what or how much to apply. But, barring making a strict track car, I would consider it virtually a requirement in any vehicle, even the FD. It's just to what degree. The sheet metal is extremely thin, the powertrain runs very hot, and we're very close to the ground.

There are a variety of products out there from dozens of brands. But they boil down to various combinations of a "mastic" -- a heavy tar-like material that dampen vibration; and various different foams that dampen sound and heat. You can get individual products and layer them. Or you can get "hybrid" products that come together in single sheets (i.e. a mastic base with a foam on top). They can run you as little as $15 of material to do a door with just a few pieces of deadener if you buy something Amazon-branded; all the way up to something literally $500/door for the uber-audiophile stuff with 4 different products stacked atop one another aimed at filling every cubic millimeter of the door cavity with various products.

Take some time looking around online for a brand at reasonable value for your budget. Buy one box each of 2 or 3 of their different products to try them out and see what makes sense for you, your goals, your budget, and what works for the individual areas you want to apply it to. I wouldn't overthink it aside from giving myself a "budget" for total weight and trying to work within that. You really can't go "wrong" aside from adding more weight than you might "need" to. Once you actually put some down, it'll make more sense. Tap a 'plain' panel and hear what it sounds like. Apply some of the product and tap it again. Add more or less and tap it again and you'll get a hang for how much/little you need to minimize resonance. And I'd focus on heat insulation products around the trans tunnel, the roof, and maybe the firewall.