Quieting the cab...

[PhoenixZorn]

My Blazer is currently undergoing an engine replacement because I was dumb... so I bought a 290hp - 380ft/lb motor that I expect will be much louder than my stock 305 was already with headers and glass packs. While I love the sound of the truck, I'm looking for a way to make my ride as quiet as possible with all the windows closed. Currently, it is so loud that if I installed a stereo, I'd have to put it at over 50% volume just to hear it... as such, I cannot hear my cell phone ring, my wife/son talking (which isn't always a bad thing) or anyone else outside the truck attempting to talk/honk at me for having such a badass truck.

So what should I do? I've heard Rhino Liner is decent for deadenning interior sound, but at $450.00 to run the liner from my pedals to the tailgate, that's kind of expensive. I plan to eventually do a custom stereo system buildup, but as it stands right now, while I have everything I need, I don't see the point since I won't be able to hear it anyway. I've also used DynaMat in the past for other stereo installs, which really works great for killing vibration and distortion, but again, the cost outweighs the effectiveness. I need some good, inexpensive suggestions, and putting mufflers on the truck is not an option since I just payed to have a high performance engine dropped in it. Plus, except for the "Ford" ram air hood scoop on it (I didn't do it, I bought it that way) it looks just like every other Blazer with a 4" lift and 31" tires... so the sound is one of the defining qualities of the truck.

Thanks in advance guys, and I'm looking forward to reading all the posts here about mods I can do to my truck without spending boku bucks on aftermarket parts. My next project is sealing the floor in the bed, as I think it's leaking really bad, though I can't tell because it's carpetted. After that, a good old fashioned fender chop and 33s will give me the coolest looking truck in my little town. The final project is the stereo, since it actually has to be warm for me to spend countless hours outside molding fiberglass boxes and housings for amps, speakers, and maybe even some lighting or video equipment.

 

[Stoopalini]

Hello, and welcome to CK5

So are you looking to quiet the cab, or the motor? If you cannot afford dynomat (or other sound deadener, I don't know any other way to quiet any SBC down without muffler(s)?

A quality exhaust system with a good muffler will not hurt the performance of your motor enough for you to notice. What is the exhaust you have now? Open headers, straight pipe, single, dual? BTW, the 350 shouldn't be much louder than the 305 was, unless you upgraded the CAM, heads, fuel delivery, or something else.

I am running a Flowmaster 70 or 80 (can't remember) series SUV muffler. This thing is pretty large, and keeps the Blazer pretty quiet until I get on the throttle.

Good luck in your search,
Thomas.

 

[Grim-Reaper]

The engine itself is pretty quite its the exhaust that makes noise. Cast iron manifolds cut down noise a lot. If you have headers that will increase the amount of volume from the engine compartment. Under hood pad helps absorb noise so its not reflected back into the cab. Header wrap might help if you run headers and then make sure the firewall pad is there. On a truck try to make sure the mufflers are not under the cab. Thats cant be helped on a K5 so make sure that the carpet has plenty of pad an a deadener like Dynomat or "Brown Bread" (search that and you should find some good info) is used.

Look for a post by I think it was "Bobk" that did some extensive sound control work on a 69-72K5. He has a detailed post on what he did with some observations.


Make sure door gaskets are sealing good and vapor mat in doors are present. they knock down a lot of noise. I just fixed a gap at the bottom of the tailgate on my 4Runner and was surprised just how much noise was coming in from a 3/8s inch gap along the bottom of the tail gate.


Bed liner material will help but thicker the better. You will get more bang for your buck out of Dynomat or other product but it leaves the potential for water getting under gaps if you ever swim the truck.

 

[hunterguy86]

if you go to www.sounddomain.com to the forums u can find info about soundproofin material similar to dynomat just much cheaper. It works just as well. I think its called Second Skin or somethin like that. I havent researched it in a while so I could be wrong. Just my .02

 

[muddyblzr]

ive heard good stuff about dynamat another thing ive seen is altamat the stuff boyd used on the alumitub for sounddeadener and insulation. i plan on putting alot in the rear wheel wells.

 

[r_pogo]

A few Suggestions:

Have not tried this... but... regular vinyl adhesive floor tiles have been used to "deaden" flat areas in the interior. I have been told it works great. These can be easily cut to fit odd shapes but don't bend very well. I would imagine the surface has to be really clean for the adhesive to stick and I don't know if it holds up over time. Some say they will hold up on vertical surfaces but I would doubt it. But CHEAP it is so using the good stuff on irregular and vertical surfaces and tiles for the flat survaces might be a good cost compromise. I will try this on the next ride.

I have used water based "elastomastic roofing sealer" (or some such name) to seal and damp the inside of speaker enclosures. This stuff goes on thick with several coats and acts like rubber, obviously usually used to seal roof surfaces so it should hold up under exterior conditions. I don't know how well it works compared to the high ticket stuff but it seems just as rubbery. See Home Depot.

On a prevous ride I took some one inch thick "semi-rigid" fiberglass insulation (denser than the usual wall insulation) and stuck it between a hot and noisy exhaust pipe/muffler and the floor board using chicken wire to hold it in place (self tapping screws held the chicken wire to the floor). It cut the sound and reduced the heat to cab -- lasted ten years.

You can glue matching regular auto carpet on painted surfaces to reduce the reflected sound inside the cab. Make a template from cardboard or paperboard to fit , then transfer to the carpet and cut. Your local auto upolstery shop can finish the edges before you glue it on. You can also try stuffing some sound absorbing foam up under the seats.

Get some kids "play-dough" wad some up and put it between the door and the door frame and close the door, once compressed you can then measure the thickness. Smetimes a strip of regular hardware store weather strip tape can add a second barrier to wind and other exterior noise that works its way past the single factory weather strip.

Some Chevy vans had specially shaped sound pads that fit tight up against the firewall. I would guess it might match other models with the same type of firewall -- maybe Balzers? See your factory truck book in the van section. Getting one of these from a junk yard might be a cheap option.

Good luck.

 

[PhoenixZorn]

A quality exhaust system with a good muffler will not hurt the performance of your motor enough for you to notice. What is the exhaust you have now? Open headers, straight pipe, single, dual? BTW, the 350 shouldn't be much louder than the 305 was, unless you upgraded the CAM, heads, fuel delivery, or something else.

Yeah... I bought a custom engine for my truck... its a 350 with 290 hp and near 400 ft/lbs of torque is going to be much louder than a stock 305 with 165hp... nothing on it is in stock form as far as I know... add that to the fact that the truck has dual straight pipes with glass packs to make it even louder, headers, edelbrock performance manifold and a holley 650 double pumper on it, means one bad ass noise maker... but good suggestions all around... whoever suggested the roofing compound, thanks, that totally slipped my mind. When I worked at Home Depot, I actually sold a guy a 5 gallon pail of that stuff to do exactly what I want to do. Just can't drive the truck for a few hours after applying it, or I'll suffocate on the fumes.


On a side note, most of the sound that I'm hearing is coming from directly below me and behind me, so firewall barriers won't help... but I'll be coating the whole truck bed pedals to gate with roofing compound as soon as the temp gets above 60 degrees consistently so I can drive with the windows down for the day...

 

[Mantruck-k5]

Undercoat spray

I used off the shelf undercoat spray on my 69 Camaro's wheel wells and under carriage. Along with the stock style sound deadener under the carpet, my interior was really quite. The stuff runs like $3 a can and can be found anywhere. I put like 3-4 coats on all surfaces. Not as good as the rhino-Liner but about $400 cheaper...

 

[PhoenixZorn]

my biggest problem is the fact that the inside was gutted, so I need to replace the stock sound deadenning mats... but yeah, I'll probably rip up the carpet, put a 1/4" of rubber on the whole bed, and re carpet it with some heavy water resistant stuff.

 

[Greg72]

Check out the "Audio" section of this site......

A keyword search on the term "Polymeric Mastic" will probably give you more information than you ever wanted to know.

In short, it's Dynamat material but at about 1/6th the price.....you can afford to lay on mulitple thicknesses. I've used it with good success...

 

[r_pogo]

Couple more tricks

In most exhaust systems backpressure is proportional to flow. So the beneifts are most noticable at high RPMs. For most low speed, part throttle driving you won't see much of the benefit of high flow mufflers. On my last ride I listened to several other cars with different setups before I decided how much noise was tolerable and figured I could do without whatever benefits would exist at higher noise levels. Still like to hear the stereo.

Still, here are a couple things you can do:

Cossover pipe. This is a short pipe that runs between the dual pipes before the mufflers. It is supposed to even out the exhaust pulses and broaden the torque curve. Good for horsepower. But I found that it also cut the peak resonant point (around 50mph) and dramatically reduced the maximum sound level. At light throttle cruise on the highway (65+) the exhaust became almost silent. At higher throttle levels it was still loud but I don't push it that often. -- all in all a good compromise.

Pipe Tip: On a sports car I had once (4 banger) I put in a less restrictive muffler but found the noise a bit high. The last couple feet of pipe were a straight shot from the kick-up bend over the rearend to the rear bumper. I cut the pipe off and welded in a straight through 30" glasspack. I then welded on a chrome tip that bent 45 degrees towards the ground just after the bumper. The glasspack (called a Cherry Bomb if I remember) completely took the hard edge off the exhaust sound and reduced the overall sound level. And it sounded VERY nice. I would guess that at this point the exhaust gasses are cooler, have condensed a bit, and the glasspack would have little, if any, effect on performance. On my next dual exhaust project I might split the duals into four pipes after the rearend kickup and put four 24" shorty glasspacks as tips. I figure the added total flow area cross section would cut residual pressure dramatically and really let the fiberglass do its work. This should allow less restriictive main mufflers without the added noise.

Of course the back end might look like a rice-burner. Ick.