Interior Noise

[dyeager535]

If anyone cares, got an interior dB number out of my truck. 103dB max. Number is under pretty constant throttle conditions, not when I was flooring it. Speed did not seem to matter too much. Random testing outside the truck at idle indicates it's louder inside than out.

It's a "cheap" Scosche SPL1000 (http://www.amazon.com/Scosche-SPL1000F-135DB-Max-Meter/dp/B001CMKFH8) so no idea how accurate it is in general, but I have already compared it to my car under same conditions/speed (85dB) which apparently is inline with "normal", so I have a baseline to compare against. It's a cheap older econobox so it is probably louder than a more expensive car.

Truck has nothing for interior that will likely affect sound: no headliner, dash pad, carpet/sound deadening. Exhaust is the stock dual pipes (for the most part) from a 6.2L spliced into headers, with no muffler on one side, and a muffler on the drivers side with a hole in the side of it. Both exhaust pipes "exit" behind the rear tire in the stock locations, but obviously the holed muffler does a pretty good of venting exhaust.

I do not like the sound. Fixed the problem that led to the blown mufflers (bad fuel pump hose in tank) but drive the truck so little that I haven't had the motivation to really dig into the exhaust, which is intended to be stainless, from the headers all the way to the back.

 

[diesel4me]

My front exhaust pipe from the manifold on my pickup's 6.2 developed a crusty layer on it last year,and it eventually lost some of the scabs,leaving holes looking like a slot behind...which make it sound like it had a ticking lifter,and stunk up the cab with diesel fumes badly when the heater was on..

Since it was sub-zero and we had 9 feet of snow fall in 30 days time,I wasn't too enthused about trying to get the nuts off the exhaust manifold's studs,which were likely to break,and there was a bolt in the third hole,not a stud,which most likely would snap off too--plus the manifolds themselves are so crusty they look like they sat on the ocean floor for 50 years...

So,in order to get me by a little longer,I took a couple of empty spray paint cans and punctured them to let all the paint and propellant out,and cut both ends off them,and slit them lengthwise with tin snips,and wrapped them around the "holy" pipe,and used several worm gear hose clamps to secure them..

To my surprise they didn't leak at all,the truck is still quiet 3 months later,and I'm not gonna TOUCH that patched up pipe it till it crumbles into rust nuggets..it is still solid other than the holes in a few spots....when its nice and warm out maybe I'll deal with that issue then...getting my leaking oil pan replaced is a higher priority ..

 

[Greg Ducato]

Damn, that is pretty loud! As I recall, my Burb is in the 70's at a 65mph cruise, full interior and extra sound deadener added though. I have a Decibel meter phone app so these are not scientific readings for sure.

 

[dyeager535]

Yeah, its beyond the threshold for hearing damage apparently, so more than I expected. It's not like you can't talk inside, but it's hard to hear, and a phone is out of the question when its running lol.

In the 70's is really good IMO! At this point the majority of the sound is the engine, but I suspect once the exhaust noise is reduced, tires will be the next issue.

What is your sound deadening Greg? I know there are a variety of products out there like Dynamat and the like.

 

[Jester1]

I was just thinking about this the other day for the '86 and the '73. '86 has standard vinyl interior, dual exhaust, 454 and the '73 has been stripped of interior, 350 single exhaust cut off just before muffler (project).

I have really been wanting to try lizard skin as I plan to put bed liner on top as an experiment to then look at doing same in '86. I am of course years away from doing it as there are bigger projects to be accomplished on both rigs first.

Has anyone else played with the product yet?

 

[Greg Ducato]

Yeah, its beyond the threshold for hearing damage apparently, so more than I expected. It's not like you can't talk inside, but it's hard to hear, and a phone is out of the question when its running lol.

In the 70's is really good IMO! At this point the majority of the sound is the engine, but I suspect once the exhaust noise is reduced, tires will be the next issue.

What is your sound deadening Greg? I know there are a variety of products out there like Dynamat and the like.

I found a foil backed Jute about 3/4" thick at a swap meet that wasn't terribly expensive and bought enough to do the roof and the floor since the headliner needed replacement and the carpets needed a good power wash. It is much cooler and quieter inside than original, the downside is the wind noise is a lot more noticeable. I'll be replacing all the door seals soon to try and help that area.

 

[dyeager535]

Good thinking on the door seals. I can still hear some on mine as the door seal is wrinkled a bit. Did you put the insulation behind the headliner, or replace the headliner?

I suspect a K5 will still tend to be noisy behind the front passenger area where a pickup may be quieter since the cab ends. On the car I noticed how different it sounds (and I think I picked up a few dB) with the rear seat folded down.

 

[Greg Ducato]

I gued it to the roof then replaced the headliner, worked out well.

 

[JoshHefnerX]

I've been into car audio for some time and at the moment the biggest gains for the buck have been making a 3 layer approach.

1. CLD - Constrained dampening layer. The foil backed butyl products. That dampens the steel via constraining w/ the foil

2. CCF - Closed cell foam. This needs to be closed cell so that it does not hold moisture. It works w/ layer 3

3. MLV - Mass loaded vinyl. Mass works to block sound and requires it be separated from the steel to create a floating floor effect.

Approx 25% coverage of cld in the center of a panel will get you about 80% of the noise reduction, as opposed to covering the entire panel in cld.

The mlv and ccf need complete coverage. They should not be glued to the steel as that negates the floating effect. On vertical surfaces you can fasten the top edge and let it drape.

Doing the loudest areas will give the most benefit, but in a blazer/suburban it's full of relatively flat surfaces and should be pretty easy to lay down. On a truck w/ no interior doing just the 3 layers I would expect at least 15db drop, probably more. I had a noticeable improvement in my modern car just doing the back seat. Dropped about 8db from factory.

I'm a ways from doing it on my Jimmy but I have the supplies already.

Josh

 

[blazinzuk]

Same approach I am gonna take in my crew cab but as has been said it will make the wind noise that much more pronounced. Still using the 3 materials approach I think will make a tremendous difference.

 

[supernaut]

If anyone cares, got an interior dB number out of my truck. 103dB max. Number is under pretty constant throttle conditions, not when I was flooring it. Speed did not seem to matter too much. Random testing outside the truck at idle indicates it's louder inside than out.

It's a "cheap" Scosche SPL1000 (http://www.amazon.com/Scosche-SPL1000F-135DB-Max-Meter/dp/B001CMKFH8) so no idea how accurate it is in general, but I have already compared it to my car under same conditions/speed (85dB) which apparently is inline with "normal", so I have a baseline to compare against. It's a cheap older econobox so it is probably louder than a more expensive car.

Truck has nothing for interior that will likely affect sound: no headliner, dash pad, carpet/sound deadening. Exhaust is the stock dual pipes (for the most part) from a 6.2L spliced into headers, with no muffler on one side, and a muffler on the drivers side with a hole in the side of it. Both exhaust pipes "exit" behind the rear tire in the stock locations, but obviously the holed muffler does a pretty good of venting exhaust.

I do not like the sound. Fixed the problem that led to the blown mufflers (bad fuel pump hose in tank) but drive the truck so little that I haven't had the motivation to really dig into the exhaust, which is intended to be stainless, from the headers all the way to the back.

Just curious: How did that fuel pump hose in tank mess up your mufflers? Was it clogged causing lean conditons and over-temp exhaust or something?

 

[dyeager535]

Just curious: How did that fuel pump hose in tank mess up your mufflers? Was it clogged causing lean conditons and over-temp exhaust or something?

Without stable fuel pressure the mixture is all over the place. The pressure was so variable that the ECM couldn't control AFR...it would end up going way rich and way lean...so rich at times that it would backfire far into the exhaust, eventually splitting the mufflers. Since I don't drive the truck often, and the problem wasn't consistent, it took me awhile to track it down, and after repeated backfiring, eventually the muffler seams gave up.