Deadening Outside Engine Sound

[Soul Shinobi]

Since removing the snorkus the engine shouts into the fender, where it resonates. My objective is to reduce engine sound, not to cabin in particular, but to the outside world--I'd like not to be paranoid of revving high.

Needless to say, this is about being discrete. Anyone interested in a more refined setup may take interest here.

I was thinking of lining the inside of the fender, including the firewall and fender liner, with a sound deadening material. I am also considering insulating the inside of the hood and engine side firewalls.

Secondarily, there are a few small areas above the muffler that could accept sound deadening material too, but that would make very little difference and would hardly be needed with my stock exhaust.


So, what the hell to use? Well I've been doing some poking around on ScoobyMods and have found a quite a few options.

First I came upon was this, a 29" x 32" self adhering sound dampening sheet for $16.50. It's heavy, weighing 5.1 lbs, that's about 0.0054957 lbs per square inch. It's said to "handle continuous temperatures -30° to 350° F." It's also available in 10" x 10" and 32" x 54" here.

Heavy, but it sounds good. Something important I need to know though is how high can the under hood temperature get in the summer for my 2.2L NA engine? Since this material turns vibration into heat, if it were to get any hotter than 250°F I'd be worried. Maybe I'm worrying too much, but I honestly have no idea what normal under hood temperatures are.

Next I found this, a 27" x 40" lightweight vinyl sound dampening sheet for $28.50. It's much more expensive, but it only weights 3.5 lbs, about 0.0032407 lbs per square inch, that's a 41% decrease in weight, nearly proportional to the raise in price, when it's said to dampen sound twice as well! So far so good, but with this there's the problem of heat. This material, though a better sound insulator, "can [only] handle continuous temperatures up to 250° F" This looks like a good candidate for the fender for sure. It is also available in 10" x 13" here.

Also worth considering from the same site is the Cascade VB-2 line which is quite a bit like the second option I mentioned in every way.

For under the hood I've just found this. Same as the sheets I just mentioned, but made for hight heat applications, up to 400°F. Seems perfect, however it's $87.45.

All of these are adhesive backed.


Now that I've bored myself to death with that, let's look at couple less obvious options. The following was said on ScoobyMods: "Ice Shield, available at most Home Depot's or Lowes is very similar. Also, HiTemp Mastic from McMaster Carr is supposed to be the EXACT same thing as dynamat at only $1.00 per SF. Part number is 9709T18."

I tried to look for an online retailer of this McMaster-Carr stuff but only came up with the phone number of the mail order catalog: (562) 692-5911. Part number 9709T18 is an "inexpensive high-temp mastic adhesive-backed material."

After some more searching I found this page. 9709T18 is not on that page but anything beginning with 9709T should be good. The heat range is only up to 175°F with these, but I think the aluminum faced sheet might reflect most heat and the adhesive side will stay below that. Bah, I'm not really sure.


I may go to Home Depot and have a look at what they have. In closing, I sound this site about sound deadening:

http://www.sounddeadenershowdown.com/

It caters to deadening sound in the cabin for a more clear audio system, so I didn't care to read it but there seems to be a lot of info on it. Man I'm exhausted.

[evolutionmovement]

You might want to make sure your exhaust gaskets are good and think about wrapping it to eliminate the biggest source of noise. Otherwise, I'd try to find some kind of plastic foam or fiberglass matting with a rubber adhesive backing. It may be cheaper and lighter than asphalt stuff. The underhood temps aren't too bad without a turbo, but I would definitely want something rated to 250 anyway. The higher the rating, the less any temp will wear on it. I would concentrate mostly on the hood and the fenders. I wouldn't do the firewall unless needed after the other parts were done since that wouldn't do as much to stop outside noise. Some butyl tape on the inside of the hood seams might help a bit, too. I had a ton of that crap from work, but got rid of it. I've built some sound-proof boxes for sound testing, but the type of material I used (box within a box lined in egg crate-type foam in a lower density than bed material) would be inappropriate for the environment under a hood. Try not to look specifically for sound deadening to buy (as it's pretty much always expensive), but search out similar substitutes. Part of the problem is that you're trying to block low frequency sound which is more difficult than high frequency (like alarms and buzzing noises I had to isolate).

McMaster sends stuff overnight free also.

[Soul Shinobi]

I'm hardly concerned about the exhaust, and don't want to wrap anything because that might accelerate corrosion.

Mind you I only have an NA engine, what do you think the underhood temp for that would be like for that?

Hood and especially the right fender are indeed my main concerns. I may even just be satisfied with the fender if that works out well.

McMaster does free overnight? That's bloody awesome.

EDIT: the second product I showed (here) was made of vinyl and made to deaden sound better than asphalt.

[evolutionmovement]

That stuff doesn't look bad at all. One question is whether the adhesive can handle the outdoor environment.

[Splinter]

The only thing that concerns me is the added weight negating the performance benefits of removing the resonators

[Soul Shinobi]

Well I would probably add 11.5 lbs with the lighter stuff or about 18 pounds with the heavy stuff. According to this nifty calculator about 21.4 pounds of weight is equal to 1 horsepower, if I enter 140 hp (I know it says enter wheel hp, but I have no idea what that would be) and 3000 lbs. I think the gains of chopping up my intake are greater than 0.55 to 0.86 hp, thankfully.