Loud Engine Room ? (Page 2/2)
Yellow-88 SEP 22, 05:37 PM

quote
Originally posted by fieroguru:

GM and other mfg. put a large focus on NVH (noise, vibration, and harshness) in the 90s and made huge strides.

One of the big things is the use of engine covers to help reduce the sound of the injectors and valvetrain noises. They also added silencers and plastic air intake filters to cut down on air flow/iac noise.



As I listen deeper in to this; I started listening to everything in the engine bay. What becomes clear is that every surface in direct contact to the engine block is a radiator. The intake manifold and the plenum alone have as much radiator surface area as a vintage JBL. The entire thing is a three way speaker array. The many heat shields reflect sound just like they do heat.

The alternator heat shield and the flat surface of its mounting bracket handle the high frequency's . The intake system and the valve covers do the mids and the exhaust system's huge surface area covers the bass. Its surface is bigger than my bass amp. The stethoscope lets one hear frequency as well as amplitude and the Fiero engine bay has both very well covered.

So yeah, some GM engineer in the late 80's listened to a 2.8 Fiero engine bay with a stethoscope. He presented his great idea at the next conference and called his new department NVH. So once again the Fiero pushes auto evolution forward. Yup ....it's true.

The VW and the Dodge both have a lot of plastic parts that radiate in both lower frequency and amplitude. The aluminum in our cars does just the opposite.
So yes, Fiero engine bays are loud.

armos SEP 22, 06:37 PM
This is subjective, but I think making cars quiet was a fad that picked up in the 1990s. I don't think car designers before that put nearly as much focus on the subject, and I don't think consumers were looking for it either.
I remember Japanese economy cars in the 90s being the first I noticed that were whisper quiet, and then everybody wanted to do the same.

I thought it was kind of weird how newer sporty cars became so generally quiet, except in the exhaust which was the only thing you could hear on them.
But that's a side effect of the same engines/etc being used in other cars where noise wasn't wanted.
Dennis LaGrua SEP 23, 11:28 AM
It must be remembered that in a Fiero your seat sits maybe 12" (or less) from the engine. On a front engine car it is mounted farther away. All of my swaps make exhaust noise as they have improved exhaust systems. That is the down side of a larger diameter pipe free flow exhaust system. If you want it quiet the stock through the CAT around the engine to the turbo style mufflers is the best way to go but valuable horsepower is lost. That could make the difference in a close race.

------------------
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82-T/A [At Work] SEP 23, 12:41 PM

quote
Originally posted by Dennis LaGrua:

It must be remembered that in a Fiero your seat sits maybe 12" (or less) from the engine. On a front engine car it is mounted farther away. All of my swaps make exhaust noise as they have improved exhaust systems. That is the down side of a larger diameter pipe free flow exhaust system. If you want it quiet the stock through the CAT around the engine to the turbo style mufflers is the best way to go but valuable horsepower is lost. That could make the difference in a close race.




I kind of wanted to mention too... because I totally get what Yellow is talking about here... but I think it's important to distinguish if we are talking about the sound that we hear when standing next to the car, or the sound we hear when we're inside the car.


I've been doing a LOT of voice recording lately for work (unprofessionally), and I've realized that WHERE you do it, not just what you do it with, makes all the difference in the world. If I'm in a room with wooden floors, a desk, and maybe a bookshelf, there's so much echo (even if I don't hear it myself). But when I'm in a room that has carpeting, a fabric couch, and some other stuff in there... the voice is so much more clear and with significantly less background echos and noise.

The same principle applies with sound in an engine bay. Inside our car, we have carpeting, seats, and all kinds of stuff that helps absorb and muffle the undesirable ambient sound. What we REALLY want to hear is the engine's roar only when / if we're really on it. But, if you go with cheaper cut-pile, go to leather seats, and remove some of the other interior pieces, you're going to hear a lot more sound. Likewise, inside the engine bay, if you remove the foam insulation from all four sides, less sound is going to be absorbed and more of it is going to be transferred to the inside of the car.

For most of us, the engine compartment insulation has deteriorated, or even collected dirt and lost it's ability to function well. It's totally different than heat-shield insulation, like what I installed in my daughter's car...




This seems to be what a lot of people are doing, as did my daughter; however, this doesn't really muffle sounds, it just prevents resonance by acting as an anti-vibration mat on the firewall (and of course to reflect some heat). But the original sound deadening did exactly just that. It was a very porous material that degrades overtime (and loses its ability to function as well). But... by being porous, it provides lots of opportunity to absorb all the **** sounds that no one wants to hear (injectors, scraping, whatever).

Seems like the more opportunity you can provide where sound can be absorbed, the better the sound quality will be. That way, you only hear the rush of the engine, and the vroom of the exhaust.


Of course, if you have a Holley side scoop, and you roll your window down... and you're using one of Rodney's direct intake tubes... it sounds like a thrashing machine in your left ear!


EDIT: to add... as the car gets older too, the seals shrink, and gaps increase, there-by allowing more sound to pervade from the outside engine noises into the cabin. I think a good heat shielding is important both inside and outside on the engine firewall... but to replace EVERYTHING ELSE... this foam stuff might be a good solution to replace the factory stuff:

https://www.amazon.com/SOOM...ation/dp/B08524VM9X/

[This message has been edited by 82-T/A [At Work] (edited 09-23-2024).]

Yellow-88 SEP 24, 08:44 AM

quote
Originally posted by armos:

This is subjective, but I think making cars quiet was a fad that picked up in the 1990s. I don't think car designers before that put nearly as much focus on the subject, and I don't think consumers were looking for it either.
I remember Japanese economy cars in the 90s being the first I noticed that were whisper quiet, and then everybody wanted to do the same.

I thought it was kind of weird how newer sporty cars became so generally quiet, except in the exhaust which was the only thing you could hear on them.
But that's a side effect of the same engines/etc being used in other cars where noise wasn't wanted.



I'm not sure it's a fad. Looking at it from physics, sound is energy. Energy can't be created or destroyed, it can only change its form. Sound energy radiating from the surface of the engine is "wasted energy". So following the laws of physics, a quite engine is more efficient. The imagined engineer that I mentioned earlier knew that.

Letting the exhaust note ring clear above the engine noise is like pulling the vocals out from a loud rock and roll stage. It aint easy. And .... there is nothing so sweet to the ears as a well tuned 60 degree exhaust note. I remember at a show, a guy asked Sweetie what she had for a sound system. She smiled and showed him those beautifully pipes tucked under the rear bumper.
82-T/A [At Work] SEP 24, 09:20 AM

quote
Originally posted by Yellow-88:

I'm not sure it's a fad. Looking at it from physics, sound is energy. Energy can't be created or destroyed, it can only change its form. Sound energy radiating from the surface of the engine is "wasted energy". So following the laws of physics, a quite engine is more efficient. The imagined engineer that I mentioned earlier knew that.

Letting the exhaust note ring clear above the engine noise is like pulling the vocals out from a loud rock and roll stage. It aint easy. And .... there is nothing so sweet to the ears as a well tuned 60 degree exhaust note. I remember at a show, a guy asked Sweetie what she had for a sound system. She smiled and showed him those beautifully pipes tucked under the rear bumper.




I don't think he's disagreeing with you, but I think he's stating that more effort was put forth in the past couple of decades to improve sound penetration. To your point, and his point, they've used newer and different materials to reduce the resonance of "everything" if you will. Plastic intake manifolds are far more common today, and will not transfer resonance (or allow the better attenuation of resonance) between the components. Same as the oil pans. Most newer cars have aluminum oil pans that are actually 1/2" thick. They're just as strong, weigh less than steal, and dissipate the sound, rather than say... my old school Iron Duke oil pan, which (as you say) acts like a resonance chamber for the moving parts of the short block.

GM (and other manufacturers) really tried to focus on improving the acoustics of the engine itself (aside from the exhaust)... for better or worse. No one wants to hear a symphony of ticking injectors, but they may want to hear the warble of an exhaust.


I'm definitely interested in this topic (if it wasn't obvious), and when I build out my 3.4 V6/60 block this Winter, I'm going to really focus on trying to improve the sound of the motor... as in, not the sound that the motor produces from the exhaust (I want to do that too), but to improve the sound the engine itself makes in the engine bay as a byproduct.

I would add Yellow... that I think the Fiero's engine was decent when new, but after ~36 years... there's a lot that's worn out that increases the undesirable sounds.
Yellow-88 SEP 24, 10:04 AM

quote
Originally posted by 82-T/A [At Work]:
I kind of wanted to mention too... because I totally get what Yellow is talking about here... but I think it's important to distinguish if we are talking about the sound that we hear when standing next to the car, or the sound we hear when we're inside the car.


I've been doing a LOT of voice recording lately for work (unprofessionally), and I've realized that WHERE you do it, not just what you do it with, makes all the difference in the world. If I'm in a room with wooden floors, a desk, and maybe a bookshelf, there's so much echo (even if I don't hear it myself). But when I'm in a room that has carpeting, a fabric couch, and some other stuff in there... the voice is so much more clear and with significantly less background echos and noise.

The same principle applies with sound in an engine bay. Inside our car, we have carpeting, seats, and all kinds of stuff that helps absorb and muffle the undesirable ambient sound. What we REALLY want to hear is the engine's roar only when / if we're really on it. But, if you go with cheaper cut-pile, go to leather seats, and remove some of the other interior pieces, you're going to hear a lot more sound. Likewise, inside the engine bay, if you remove the foam insulation from all four sides, less sound is going to be absorbed and more of it is going to be transferred to the inside of the car.

For most of us, the engine compartment insulation has deteriorated, or even collected dirt and lost it's ability to function well. It's totally different than heat-shield insulation, like what I installed in my daughter's car...

This seems to be what a lot of people are doing, as did my daughter; however, this doesn't really muffle sounds, it just prevents resonance by acting as an anti-vibration mat on the firewall (and of course to reflect some heat). But the original sound deadening did exactly just that. It was a very porous material that degrades overtime (and loses its ability to function as well). But... by being porous, it provides lots of opportunity to absorb all the **** sounds that no one wants to hear (injectors, scraping, whatever).

Seems like the more opportunity you can provide where sound can be absorbed, the better the sound quality will be. That way, you only hear the rush of the engine, and the vroom of the exhaust.




Everything A/T is saying here is right on. Sound energy can be easily absorbed, or transferred from mechanical to heat by "soft" materials. And ... different frequencies can be absorbed by different materials. We can't do anything about the actual sound energy radiating from the surfaces of our engines but we can absorb a lot of it after it gets out. I think that the over stuffed interiors approach used in the 80's was part of what contributed to the "numb" feeling. That's like listening to studio monitors in a giant soft chair wearing a fluffy hat. It sounds OK but one does miss some important stuff. The mixing and mastering engineers are paid more than the rock stars for a good reason. If one wants to look good as a sound guy, work only with outdoor venues.

If I get a chance to build my last Fiero project, (Yellow 2.0) it will include some tightly fitted acoustic mat instead of the mouse house material Detroit uses. Large flat panels like the firewall probably have some interesting resonance properties and I think Detroit's approach can be improved upon.

If one wanted to get really involved. one could probably choose what frequencies are most annoying and reduce those. That's probably what's going on in modern "auto acoustics".