# How to quiet down underhood noise



## Sr SQ (Dec 8, 2006)

Okay guys I have been reading for days on the topic of noise isolation and soundproofing and it seems the more I learn the less I understand????
My current truck is a 2003 Ram quad cab with a twin turbo Cummins, while this newer style common rail engine is much quieter than the privious ones I have owned it still sounds like a 747 jet engine is going to suck the glove box out when the turbos spool up.
In my reading I have read that much of the interior cabin noise comes from the hood/cowel area and thru the windshield?
If this is true than what would the best route for me to use with the materials at hand or what other route would you suggest?
I have a large quantity of 3/32 lead sheet (approx 2'x3' pieces)
a couple of rolls of BXT and lots of 1/8" neopreen for this install.
I really cant see glue holding the lead sheet to the underside of the hood so I think that will be out?


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## gijoe (Mar 25, 2008)

Think about how the noise is getting into the cabin. Most of it is coming through the firewall. So if you are serious about fixing the issue, you're going to have to gut the dash and deaden the crap out of the firewall. This isn't going to an after work project, more like a extra long 4 day holiday weekend project. I'm sure deadening the hood will help a little, but I don't think it'll make a huge difference, and I probably wouldn't go through the effort to load the hood up with lead.


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## Sr SQ (Dec 8, 2006)

I have full intentions of wrapping the entire cab except the roof with the lead but I had read many refferences to the hood being a large offender as well.
In the interior I feel confident that contact cement will hold the sheet in place but not so much under the hood.
If its not true than I can save some effort but since my hood doesn't even have a factory pad so I figured there would be lots of room for improvment?


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## 60ndown (Feb 8, 2007)

to seriously deaden a noisy truck takes hours and hours (40+ @ $50 an hour =$2000) of time and lots of $$ (700+) in product.

$2700.00

another option is to sell your current truck and buy something quieter.


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## Billy Mays (May 11, 2009)

dynamat extreme or second skin's asphalt based deadener would work on your hood and firewall as long as you cleaned the surface first. i'm thinking about doing this under the hood. i'd like some legit answers to this as well. not really interested in gutting the dash and putting it back in but i'm probably going to do the rest of the car with asphalt based product and then second skin's "luxury liner" over top of that once i have the cash monies.


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## Sr SQ (Dec 8, 2006)

60ndown said:


> to seriously deaden a noisy truck takes hours and hours (40+ @ $50 an hour =$2000) of time and lots of $$ (700+) in product.
> 
> $2700.00
> 
> another option is to sell your current truck and buy something quieter.



Thanks for the reply


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## Sr SQ (Dec 8, 2006)

Billy Mays said:


> dynamat extreme or second skin's asphalt based deadener would work on your hood and firewall as long as you cleaned the surface first. i'm thinking about doing this under the hood. i'd like some legit answers to this as well. not really interested in gutting the dash and putting it back in but i'm probably going to do the rest of the car with asphalt based product and then second skin's "luxury liner" over top of that once i have the cash monies.


Yes the dash will be out with the rest of the interior.
The underside of the hood is an area that worries me due to the heat. I think the BXT will stick fine but it won't do much to isolate the engine noise? Mainly looking for options.


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## Billy Mays (May 11, 2009)

Sr SQ said:


> Yes the dash will be out with the rest of the interior.
> The underside of the hood is an area that worries me due to the heat. I think the BXT will stick fine but it won't do much to isolate the engine noise? Mainly looking for options.


if your truck is older you might do some justice to it by replacing the engine mounts. or just the rear mount depending. theory being if you can stop the vibration you can stop the noise.


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## cvjoint (Mar 10, 2006)

gijoe said:


> Think about how the noise is getting into the cabin. Most of it is coming through the firewall. So if you are serious about fixing the issue, you're going to have to gut the dash and deaden the crap out of the firewall. This isn't going to an after work project, more like a extra long 4 day holiday weekend project. I'm sure deadening the hood will help a little, but I don't think it'll make a huge difference, and I probably wouldn't go through the effort to load the hood up with lead.


What he said plus you could get the engine out and spray some deadener on the firewall on the engine bay side. It's a lot of work, I wouldn't go though with it because I love turbos. You can recirculate the blow off valve if that's not done yet.


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## 60ndown (Feb 8, 2007)

lots of heat resistant products glue available for firewalls/engine compartments. if your really going to do this i recc you strip the truck as far as you can go, and deaden everything you can, dont miss even 1 spot (or you might be doing this job twice), do everything.when the truck is stripped, spend 5 min utes 'tapping' on any bare metal you can see with a wooden screwdriver handle. f there is any 'ring' or 'resonance' deaden it.fill cavities you cant reach into with expanding foam, drill holes so foam can expand out and not warp metal.

but my guess is, even if done correctly, you are going to be dissapointed with the results, because your truck is very noisy from the start.

start with a quiet vehicle, and deaden it, and you get an almost silent vehicle.


start with a noisy vehicle, deaden it, and you might improve things if the offending noise is at the same frequencies the deadening material was designed to combat..



Sr SQ said:


> My current truck is a 2003 Ram quad cab with a twin turbo Cummins, while this newer style common rail engine is much quieter than the privious ones I have owned it still sounds like a 747 jet engine is going to suck the glove box out when the turbos spool up.


most deadener is designed to kill road/wind noise (70 db @ 20-1000hz) 

^ looks to me like your major problem is 'whine' (5000-15,000hz) typical deadening wont touch that.


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## Sr SQ (Dec 8, 2006)

cvjoint said:


> What he said plus you could get the engine out and spray some deadener on the firewall on the engine bay side. It's a lot of work, I wouldn't go though with it because I love turbos. You can recirculate the blow off valve if that's not done yet.


I was thinking of removing the factory foil pad and spraying the engine bay firewall but was unsure if that will actually help stop the noise from the engine.
Negative on the BOV, it's a diesel


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## guitarsail (Oct 12, 2007)

Billy Mays said:


> dynamat extreme or second skin's asphalt based deadener would work on your hood and firewall as long as you cleaned the surface first. i'm thinking about doing this under the hood. i'd like some legit answers to this as well. not really interested in gutting the dash and putting it back in but i'm probably going to do the rest of the car with asphalt based product and then second skin's "luxury liner" over top of that once i have the cash monies.


None of these products are asphalt based...I'm surprised ant or someone else hasn't come rolling through this thread....



60ndown said:


> most deadener is designed to kill road/wind noise (70 db @ 20-1000hz)
> 
> ^ looks to me like your major problem is 'whine' (5000-15,000hz) typical deadening wont touch that.


CLD "deadening" doesn't do anything for road/wind noise....
It simply constrains vibrations and resonance on panels...
Barriers block noises...a combo of both does well...but CLD's don't do **** for road/wind noise....my Saturn was a great example of that...


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## Sr SQ (Dec 8, 2006)

60ndown said:


> lots of heat resistant products glue available for firewalls/engine compartments. if your really going to do this i recc you strip the truck as far as you can go, and deaden everything you can, dont miss even 1 spot (or you might be doing this job twice), do everything.when the truck is stripped, spend 5 min utes 'tapping' on any bare metal you can see with a wooden screwdriver handle. f there is any 'ring' or 'resonance' deaden it.fill cavities you cant reach into with expanding foam, drill holes so foam can expand out and not warp metal.
> 
> but my guess is, even if done correctly, you are going to be disappointed with the results, because your truck is very noisy from the start.
> 
> ...


It's actually a pretty quite truck compared to my last two but as you said it's not like a luxury sedan by any stretch of the imagination.
I was able to make pretty good improvements with my older Dodges with just deadener and foam so I thought if I went the extra mile with this one and added the lead sheet to the mix.......?
Any recommendations for a product to use to target the turbo whine, a foam?


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## 60ndown (Feb 8, 2007)

Sr SQ said:


> Any recommendations for a product to use to target the turbo whine, a foam?


if i were you, id spend 5 minutes on the phone with,

antony from second skin 

and 

rick from rammat.

before i did anything.

_*its their buisiness*_ to know what you should do.

others, unless they have actually don it in your situation,

are guessing.


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## guitarsail (Oct 12, 2007)

Sr SQ said:


> It's actually a pretty quite truck compared to my last two but as you said it's not like a luxury sedan by any stretch of the imagination.
> I was able to make pretty good improvements with my older Dodges with just deadener and foam so I thought if I went the extra mile with this one and added the lead sheet to the mix.......?
> Any recommendations for a product to use to target the turbo whine, a foam?


There isn't a deadener that will target turbo whine...

You need to do layers as is recommended for all noise etc. Deaden the metal for vibration and dampening, then blocking layers. Lead, MLV etc....


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## Sr SQ (Dec 8, 2006)

guitarsail said:


> None of these products are asphalt based...I'm surprised ant or someone else hasn't come rolling through this thread....
> 
> I figured it was just a typo on his behalf, I know the Rammat I have is a butyl
> 
> ...


As far as I can figure the aluminium foil does do a little for stopping noise but for the most part the product isn't designed to stop noise, thats why I planned on using the lead sheet. My concern is hanging the lead on the underside of the hood. I know MLV would work also but that would leave me the same issue of how to mount it as its almost a heavy?


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## 60ndown (Feb 8, 2007)

Over Kill Pro™ is a very flexible OEM style foam made of closed cell vinyl infused with rubber, specifically engineered to absorb airborne noise in your doors between the frequency range of 15k Hz and 20k Hz. It is 3 times thicker than our regular Overkill mat and will do 3 times the work.

Over Kill Pro - Acoutic Car Audio Noise Filter and Noise Barrier

make the callz .........


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## Genxx (Mar 18, 2007)

For under the hood Dynamat makes a hoodliner. I hear it works pretty good. I have to deal with same as you driving a Ford Powerstroke.

Lead will work on your firewall inside but the only way I know off to get it to truly stay is to use a sandwich technique. Place it between layers of deadener. I will tell you do not place it directly on the firewall lead against the metal will vibrate and cause more noise.

Also MLV will work. Contact cement works decent to get it to hold in place but you are going to have to get creative to figure out a way to get it to stay. Best way would be to spot weld some points onto the firewall that use the slide on things to secure it.

This is my recommendation and its a PITA.

One layer of of Cascade TG-1
Then a layer of Deadener
Next the Lead sandwhiched between the first layer and next layer of deadener. 
Then if you can fit it a layer of MLV over that. Make sure you seal the edges of the MLV on the sound will get around it.

Then do the hood with either Dynamat Hoodliner or Cascade VB-TS.

You still will not get rid of all the engine noise the best you can hope for it cut it down some.

I played around in my truck but IMO it was to much of a PITA for the outcome.

I can turn my system up loud enough to get over tire and engine noise and it still sounds great so I dropped trying to get rid of the engine noise.

Have fun and if you decide to try and see how much noise you can actually get rid of do a "how to" or "review".


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## bobduch (Jul 22, 2005)

Yes you can do things that will help a lot. 
In answer to your question, yes the hood work will help too.
You are talking 3 things here:
1) deadener-reduces vibration
2) barrier-reduces noise passing through
3) absorber-absorbs sound waves, the lower the frequency to be absorbed the thicker the material must be. Check out Owens Corning web site-in particular, Black Acoustic Blanket. Also a nice tutorial on what it takes to absorb sound.

Your getting noise through the widshiel, firewall AND wheel wells. 
This is what I would do with your truck (similar to what I did with my van).
Powerwash outside wheel wells. Spray on a few layers of rubberized undercoating from your local auto parts store.
Layer of deadener over inside wheel wells and firewall.
Layer of barrier over that. (Some of your lead maybe too)
If I had the room I would then do an 1" plus layer of absorber-this might work against some of the firewall, probably not under carpet over wheel wells.
Engine side of firewall I used 3/4" hoodliner foam.
My hood was also bare metal. Used the same hoodliner foam and then over that used the Honda factory hoodliner that came out the year after I got my van. And yes it fit over the 3/4" foam.

The biggest problem I see with lead under the hood is will you be able to open/keep the hood up when checking the oil?

I used Scosche AMT060 deadener, AMT250 barrier and AMT750 hoodliner. I like their stuff and I got it at dealer cost. I also used some OC acoustic blanket. Sadly, it is now a minimum order of 8k sq. ft.

This is extreme but your defroster/heater intake is probably near the windshiel/hood intersection. Can't block that off. Unless you move your intake somewhere away from the engine.


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## Billy Mays (May 11, 2009)

60ndown said:


> Over Kill Pro™ is a very flexible OEM style foam made of closed cell vinyl infused with rubber, specifically engineered to absorb airborne noise in your doors between the frequency range of 15k Hz and 20k Hz. It is 3 times thicker than our regular Overkill mat and will do 3 times the work.
> 
> Over Kill Pro - Acoutic Car Audio Noise Filter and Noise Barrier
> 
> make the callz .........


Noise Reduction Uses...

Many people use closed cell foam materials like Overkill Pro on top of vibration mats, but this does very little for noise reduction.

Unfortunately there are several companies out there marketing cheap closed cell foam as noise barriers, and we are left to combat poor marketing by educating our customers on how things really work.

Mass is key when reducing airborne noise, and closed cell foams simply do not have the mass that is required to effectively do the job.

For reducing airborne noise, Overkill Pro will help some, but not nearly as much as our barrier product Luxury Liner and Luxury Liner Pro.


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## pontiacbird (Dec 29, 2006)

Don't forget the air induction vent for the HVAC of the automobile. It's a wide open hole, usually under the windshield wiper motor housing. I think this is letting a MAJORITY of the noise into the car directly. A way to combat this would be to add some sort of foam in the intake area of the HVAC....


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## Rudeboy (Oct 16, 2005)

Gutting the interior and treating the hood are orders of magnitude away from each other in terms of the effort required. Since you are already committed to gutting the interior, do that first. Once you have treated the firewall, doors, back wall and roof?, you will be in a much better position to determine if your hood/engine compartment needs any more work. When you reduce the most problematic noise sources it's easier to tell what's left to do.


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## FoxPro5 (Feb 14, 2006)

Sr SQ said:


> I have a large quantity of 3/32 lead sheet (approx 2'x3' pieces)
> a couple of rolls of BXT and lots of 1/8" neopreen for this install.


Lead is usually 1 lb/sqft at 1/64", so you're at 6 lbs/sqft. That's some heavy ****!!  Figure your hood at least 16 sqft and you're talking nearly 100# of added weight. Great for shoulder press workout, but bad for everything else. Hell you'd need a hydrolic press just to get that thing up. 

I ran some predictions if you put a single layer (no seams) on your firewall. Say the ingress at WOT is 100 dB, then....
50 hz goes down to 85 dB (-15 dB)
100 hz goes to 79 dB (-21 dB)
250 hz goes to 71 dB (-29 dB)
500 hz goes to 65 dB (-35 dB)
750 hz goes to 62 dB (-38)
2000 hz goes to 53 dB (-47)

You can also play with adding mass. For simplicities sake, lets keep the noise at 250 hz. So with one layer we went from 100 dB to 79 dB. To your ears that will seem like a 2x reduction in noise because every change in 10 dB equates to either halving or doubling the noise (A weighted). Adding more...
2 layers gets you down to 65 dB (-35 dB)
3 layers gets you down to 59 dB (-41 dB)....

If you look at the trend here you will see a 6 dB change when you either double/halve the mass or go up/down an octave (2x or 1/2 change in the frequency). This is Mass Law...and yes it's a law which means any foam, cotton, metal, glass, etc must obey. 

This is your homework reading. Don't ask me any questions until you've read it at least once because I won't answer them. But maybe someone else can misguide you in the mean time....
E-A-R Specialty Composites


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## Sr SQ (Dec 8, 2006)

Excellent!
Thanks to everyone for their replies, you all have been very helpful.

pontiacbird
I was thinking about the HVAC and all the plastic tubes.
I figured I would look closer at them once I got it apart.

Rudeboy
I probably will have to go the route you suggest as these projects usually take me more time than I budget for.

Foxpro5
Unfortunately the lead is the only thickness I can get it free.
I wasn't to overly concerned about adding a few hundred pounds to the weight of the truck (sits at 8400# with me in it now) but I knew there was no feasible way to add it to the underside of the hood.
Thanks for the link, got to go to sleep now but will read it over tomorrow.


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## guitarsail (Oct 12, 2007)

First dibs on some of Sr SQ's free lead in exchange for our advice... 


No seriously though....


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## ANT (Oct 15, 2005)

Mos tof our customers go with a gallon of Spectrum as a hood coating.
Works very well!




Billy Mays said:


> dynamat extreme or second skin's asphalt based deadener would work on your hood and firewall as long as you cleaned the surface first. i'm thinking about doing this under the hood. i'd like some legit answers to this as well. not really interested in gutting the dash and putting it back in but i'm probably going to do the rest of the car with asphalt based product and then second skin's "luxury liner" over top of that once i have the cash monies.


Since when did Second Skin become asphalt based?

ANT


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## FoxPro5 (Feb 14, 2006)

DIYMA said:


> Since when did Second Skin become asphalt based?


Since Obama took office. Instead of using the latex from recycled condoms to blend with the other mysterious black goo found in butyl, they switched back to asphalt. Critics say it's a way to socialize deadening. Check with your supplier, it's like totally like legit and stuff. :surprised:


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## FoxPro5 (Feb 14, 2006)

Sr SQ said:


> Foxpro5
> Unfortunately the lead is the only thickness I can get it free.
> I wasn't to overly concerned about adding a few hundred pounds to the weight of the truck (sits at 8400# with me in it now) but I knew there was no feasible way to add it to the underside of the hood.
> Thanks for the link, got to go to sleep now but will read it over tomorrow.


You bet. I didn't mean to sound like a prick earlier, just to make sure you follow up on the reference first. So many don't and just expect us who've done our homework and have dug in every nook and cranny in a car to give them detailed instructions all wrapped up in a pretty bow. 

But can I ask where you're getting that heavy of lead sheeting in that quantity? It's not exactly cheap. I paid $6 lb for 1/32" just before the prices doubled.


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## Sr SQ (Dec 8, 2006)

DIYMA said:


> Mos tof our customers go with a gallon of Spectrum as a hood coating.
> Works very well!


Thanks ANT will PM you.





FoxPro5 said:


> You bet. I didn't mean to sound like a prick earlier, just to make sure you follow up on the reference first. So many don't and just expect us who've done our homework and have dug in every nook and cranny in a car to give them detailed instructions all wrapped up in a pretty bow.


No worries, you didn't come off that way at all.
I totally understand and really appreciate your help, that link was very informative. 
I think the only thing it left me unsure of at this point is weather or not my foam will work. I have a large amount of 1/8" neoprene that I planed on layering as a barrier but reference was made to a open cell foam. Will it make a difference for the barrier between the dampener and the lead?



> But can I ask where you're getting that heavy of lead sheeting in that quantity? It's not exactly cheap. I paid $6 lb for 1/32" just before the prices doubled.


If I told you I have been melting it down for downrigger cannon balls would you stop giving me advice?
I was given close to 1k# by a guy who worked for the local electric company.
They use it to wrap the wire splices underground/water or something?
After reading one of your posts about how good the lead sheet works to stop noise I held off on melting the rest down. Pretty sure I have enough left to do the inside of the truck.


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## FoxPro5 (Feb 14, 2006)

Sr SQ said:


> I have a large amount of 1/8" neoprene that I planed on layering as a barrier but reference was made to a open cell foam. Will it make a difference for the barrier between the dampener and the lead?


Read the article. A damped decoupled barrier should theoretically outperform an undamped one. But it depends on if the substrate (your firewall) is resonant. Most firewalls are not long and flat, they're convoluted and have holes all over them. My felling is that putting your RAAM down is just a waste. Better off treating those holes and trying to make the barrier decoupler composite (lead + foam) as continuous as possible, wide and tall. Get that decoupler layer as thick as you can, would be my suggestion. Noise wants to get in and will if you let it. Make the windshield the last resort IMO.


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## Sr SQ (Dec 8, 2006)

OK Fox, thanks for all the info.
Hopefully I will have it apart by the end of the month.
Will post up my results when done.


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