What Causes the Noisy Sounds of Engine Performance?

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The discussion centers on the sources of engine noise, particularly the sounds produced during operation. Key contributors to engine noise include combustion noise, exhaust gases, and the shockwaves created by expanding gases when the exhaust valve opens. The participants clarify that while combustion noise is significant, the repetitive "kicking" sound often associated with engines is primarily due to exhaust pressure pulses. Differences in engine types, such as air-cooled versus liquid-cooled engines, affect the audibility of these sounds, with air-cooled engines producing more distinct noise from combustion. Overall, the complexity of engine sounds is influenced by various factors, including engine design and exhaust systems.
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hi to all, this is my first post here n quite a stupid one:shy::shy:
last day i had a discussion with my friend over this..
what exactly is the reason behind that sound of the engine?
i mean is it the sound of the explosion of the charge or is the sound of the expanding gases comin out to the muffler from the exhaust of the engine?
 
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A big mixture.

Depending on what the engine is installed in, the biggest sources of noise are exhaust gases, induction roar, fan noise (and that of belts, pulleys and other rotating components), and combustion noise from the resonating engine parts.

Big, 'flat' components like gearcases, sumps and rocker covers are prime resonating panels.
 
nahh i don't mean that, i mean the typical sound of the repetetive strokes. i mean, the sound of those contineous kicks, is it bcoz of the explosion of charge or bcoz of its expansion when outlet valve opens?
 
Combustion noise, exhaust noise, and a bit of induction noise.
 
nah dude... u r still not getting it
 
buster said:
nah dude... u r still not getting it
I thought Brews answered exactly what you were asking. It is tough to figure out what you are asking based on your descriptions.

Combustion noise would be my number one guess to the noise signature of an auto engine.
 
buster said:
nah dude... u r still not getting it
What do you mean brewnog isn't getting it? He's answering the question you asked (though the question you asked might not be the the one you wanted the answer to). Care to try again?
 
buster said:
..or bcoz of its expansion when outlet valve opens?

Yup, that's the loudest source of the sound. Specifically, the shockwave produced by the expansion in addition to other moving parts.. But in air-cooled engines, a little sound could be heard from the explosion of the mixture, adding to the frequency of the 'kicking' noise. It's hardly heard in a liquid-cooled engine because the water channels surrounding the cylinders muffle that sound.
 
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gaming_addict said:
Yup, that's the loudest source of the sound. Specifically, the shockwave produced by the expansion in addition to other moving parts.. But in air-cooled engines, a little sound could be heard from the explosion of the mixture, adding to the frequency of the 'kicking' noise. It's hardly heard in a liquid-cooled engine because the water channels surrounding the cylinders muffle that sound.

yes yes... that's what i m tryin to ask... is it bcoz of the shockwave of the outgoing gases or the explosion of charge??
my initial guess was the shockwave thing
 
  • #10
i just had this debate with some friend.. that's why i asked u guys to get some clarification.. i m actually talkin abt the dak-dak-dak sound(i know i sound silly, but this is the only way left,hehe) of the strokes.
ok imagine it this way, if an engine is running at very low rpm, u can hear to its stroke sounds very distinctly, that is what i m talkin abt...
or imagine the machine the grandpa used in Mr Bean-The holidays(where the grandpa has installed an engine on his bycycle n which is ridiculously slow, hehe, there u can hear it clearly)
 
  • #11
gaming_addict said:
Yup, that's the loudest source of the sound. Specifically, the shockwave produced by the expansion in addition to other moving parts.. But in air-cooled engines, a little sound could be heard from the explosion of the mixture, adding to the frequency of the 'kicking' noise. It's hardly heard in a liquid-cooled engine because the water channels surrounding the cylinders muffle that sound.
Source please.
 
  • #12
FredGarvin said:
Source please.

http://www.nsxprime.com/FAQ/Miscellaneous/exhausttheory.htm and leave some to experience.

buster said:
..
or imagine the machine the grandpa used in Mr Bean-The holidays(where the grandpa has installed an engine on his bycycle n which is ridiculously slow, hehe, there u can hear it clearly)

It's the muffled sound of the exhaust pulses :) 'Exhaust Pulse'(formal term), 'Pressure waves', 'Shockwaves' are common terms among automotive people which is the explosive expansion of the gases when the exhaust valve opens.

my initial guess was the shockwave thing

You're correct, keep in mind though that though may sound a lot different from one engine to the other (factors as exhaust system and engine design, RPM) or even resemble another sound like clapping sticks. It's basically the exhaust pulses which is caused by the explosive expansion of high pressure gases liberated by the rapidly opening valve during the exhaust stroke.

However in situations that the exhaust system is doing an excellent job of absorbing the engine noise, you won't hear those pulses, the fan/motor noise could be even higher.

For air-cooled engines, a small percentage comes from the ignited mixture. We once had an air-cooled VW beetle. When checking the exhaust system for leaks, we'd sometimes momentarily cover the exhaust pipe, and still hear 'clicking' sounds coming from the cylinder fins. On a liquid-cooled engine, covering the pipe, and you'll hear nothing =)
 
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  • #13
nice link over there gaming addict.
thnx
 
  • #14
gaming_addict said:
http://www.nsxprime.com/FAQ/Miscellaneous/exhausttheory.htm and leave some to experience.
There is nothing in that link that references expansion shocks as you stated.

gaming_addict said:
Yup, that's the loudest source of the sound. Specifically, the shockwave produced by the expansion in addition to other moving parts..

That source does talk about pressure pulses which are due to combustion, i.e. combustion noise.
 
  • #15
but combustion noise r the cause n pressure pulses r the effect..
what i wanted to know was that the typical sound signature is bcoz of that explosion(combustion noise) or the pressure(exhaust) pulses..
n i think it is the pressure pulses
 
  • #16
I own a Mazda 6. The exhaust of the Mazda 6 was tuned, not for engine performance, but to provide a pleasing noise. And, of course, it sounds different if you are standing in front of it than if you are standing behind it! The sound a car makes is a complicated thing and I still don't think you are understanding the complexity in your own question.

gaming_addict, I know you are just trying to help, but a lot of what you are saying (not just in this thread) is based on misconceptions and oversimplifications and isn't necessarily true. As a matter of procedure, we prefer technical information be sourced - and this would be helpful in your case, as it would enable you to verify that you have the answer correct before giving it.
 
  • #17
buster said:
but combustion noise r the cause n pressure pulses r the effect..
what i wanted to know was that the typical sound signature is bcoz of that explosion(combustion noise) or the pressure(exhaust) pulses..
n i think it is the pressure pulses
Unless you are used to hearing engines running without mufflers and resonators, then the exhaust system plays a large role in that as well. The company my sister works for has developed a new system that includes a digital sound sampling system in the muffler to actually tune the exhaust noise to make your car sound like a different kind of car. It's pretty cool.

The German-based supplier already has a prototype tuned-exhaust system installed in an Audi A4 2.0L Turbo that can produce up to five different tones, a company official tells Ward’s on a tour of the facility here. The acoustical technology also includes an active silence system,which cancels exhaust noise by using a microphone and speaker embedded in the muffler that produce “anti-noise,” effectively canceling out most exhaust sounds. By suppressing or amplifying the exhaust noise produced during the firing of a vehicle’s cylinders, the tuned system can make a 4-cyl. car sound like a V-8 model or vice versa, depending on the driver’s preference.

http://wardsauto.com/about/WAR_sample.pdfJust to be nit picky again, the combustion process is a controlled burn/deflagration. It is not an explosion. If the mixture were to explode that is referred to as a detonation and that detonation and increases wear and decreases performance of the engine.
 
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  • #18
But in a more specific manner, while the combustion is the main source of energy of the pulse, the pulse is not produced until the valve is quickly opened on the exhaust stroke (the fourth and last stroke in a 4 stroke engine).

Combustion noise, actually, I haven't heard of that term yet, but if this is the noise from the combustion itself, happening at the same time. Then it's not the main source of the sound you described. On an air-cooled engine, that sound resembles a clicking sound(not from the valves) and is quite similar to the sound produced by a gun with silencer. It's an old VW, engine, so it might have a unique sound signature. The sound from the pulse, is deeper(lower tone or bassy) and louder.
 
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  • #19
FredGarvin said:
Just to be nit picky again, the combustion process is a controlled burn/deflagration. It is not an explosion. If the mixture were to explode that is referred to as a detonation and that detonation and increases wear and decreases performance of the engine.

In layman's terms, that's called 'knocking' caused by using fuel with octane ratings below the recommended for a particular engine. :)
 
  • #20
gaming_addict said:
Combustion noise, actually, I haven't heard of that term yet, but if this is the noise from the combustion itself, happening at the same time. Then it's not the main source of the sound you described.
If you are at all familiar with high-performance engines, then you know that the whole point of headers is to equalize the distance that the exhaust pulses must travel. This puts them into a compatible frequency that minimizes reversion, and thus lowers the back-pressure. Same idea for a cross-over pipe, or 'H' pipe, or whatever you want to call it. Given two identical engines, you can definitely tell by the sound which one has stock exhaust and which one has headers.

gaming_addict said:
On an air-cooled engine, that sound resembles a clicking sound(not from the valves) and is quite similar to the sound produced by a gun with silencer.
I must assume from this statement that you haven't had other than a Hollywood exposure to 'silencers'. To start with, there is no such thing. There are various efficiencies of 'suppressors'. Not one of them sounds anything like a movie 'silencer'. A really good one for a .45 will maybe make it sound like an unsuppressed .22, and it's about the size of a 5-cell flashlight.
 
  • #21
russ_watters said:
The sound a car makes is a complicated thing and I still don't think you are understanding the complexity in your own question.

i m not talking about the sound of the car. i know that it is various things(like AC, dynamo etc) that makes up the sound of the car. what i m talking about is the engine sound
 
  • #22
FredGarvin said:
The company my sister works for has developed a new system that includes a digital sound sampling system in the muffler to actually tune the exhaust noise to make your car sound like a different kind of car.

:devil:
Oh, man... a whole new dimension to the world of Q-ships. :biggrin:
So when I stuff that blown and injected 392 hemi into the backseat of the DS19 Citroen, I can make it sound like a 4-cylinder? :devil::biggrin::devil::biggrin::devil::biggrin:

buster said:
this is my first post here n quite a stupid one
One thing that we tend to point out a lot in PF is that there's no such thing as a stupid question... as long as it's a legitimate endeavour to gain knowledge.
In your case, though... you've been given the answer to your question several times, in several different ways, by several different people, and you won't accept it. That, to me, is an indication of stupidity.
 
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  • #23
Danger said:
:devil:
Oh, man... a whole new dimension to the world of Q-ships. :biggrin:
So when I stuff that blown and injected 392 hemi into the backseat of the DS19 Citroen, I can make it sound like a 4-cylinder? :devil::biggrin::devil::biggrin::devil::biggrin:
What's a "q-ship?"

Yes. That is kind of the idea behind the system (as I understand it). It is two fold: 1) to reduce the external sounds emitted and 2) to tune the exhaust to provide a sound that is pleasing to the owner. Now, I'm not sure they're going to include the "mosquito on steroids" sound that so many "young adults" like to have on their Honda Civics...
 
  • #24
Hi, Fred.
'Q-ship' is another term for a 'sleeper', or a wolf-in-sheep's-clothing. The point is to have a balls-out racing machine that looks and sounds like a dead-stock car (preferably old and on its last legs). When one of those 'mosquito' drivers or some idiot in a Porsche tries to give you a hard time at a stop-light... :biggrin:
The term comes from the old British Admiralty. When pirates abounded, the Brits put facades on full-blown warships to make them look like merchants. If a pirate attacked, they'd drop the sidewalls to reveal a few dozen cannons. Game over.
 
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  • #25
Ahhhh...I've heard the "sleeper" term.

Ya learn something new everyday.
 
  • #26
One thing that really surprised me is that if you have a car that looks rather hot, most people assume that it's false bravado with nothing to back it up.
I remember about 25 years ago, when I was still driving the Roadrunner, I pulled into the local Mohawk for some go-juice. There was a very large and obvious '440' printed on each of the hood nostrils, and 650hp pumping through a pair of Baby Thrush mufflers bolted directly to the headers with no tailpipes. The 17-18 year old pump jockey's eyes widened and he said 'Wow... nice. What's in it, a 318?'
I'm like, 'Yeah, kid, that's what it is. Wanna go for pink slips?' :devil:
 
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  • #27
Danger said:
In your case, though... you've been given the answer to your question several times, in several different ways, by several different people, and you won't accept it. That, to me, is an indication of stupidity.

:smile::smile::smile:
that is exactly why i told u it was stupid..
infact in this debate with my friends, i wasted almost 3 hours. i know there cannot be a particular reason for the engine sound signature, but what i m tryin to ask is about the sound of the strokes, that is where we had the debate.:biggrin::biggrin:
n sorry for talkin stupidly again..
 
  • #28
Danger said:
Hi, Fred.
'Q-ship' is another term for a 'sleeper', or a wolf-in-sheep's-clothing. The point is to have a balls-out racing machine that looks and sounds like a dead stock car (preferably old and on its last legs).

pretty funny stuff over here...:smile::smile::smile::smile:
 
  • #29
buster said:
pretty funny stuff over here...:smile::smile::smile::smile:

Where's 'over here'? I've been assuming that you're a Yank (no offense intended).
This link might help a bit; it's based upon the unique sonic signature of Harley-Davidson bikes.
http://www.bc.edu/bc_org/avp/law/st_org/iptf/articles/content/1998101101.html"
 
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  • #30
aaaaaaaaa... what's a YANK?
 
  • #31
A citizen of the USA.
 
  • #32
that link was indeed helpful.. infact that was the sound i m talkin about. that potato-potato-potato sound.
n cud they possibly trademark that sound? i mean some crazy scientist can do his stuff on his stupid bike's exhaust system n get it to roar like a HARLEY! what then?
 
  • #33
Danger said:
Where's 'over here'?

on PF... where else:-p:-p
 
  • #34
PF isn't over here... it's just HERE. :biggrin:

Be educated... be very educated... :rolleyes:
 
  • #35
Danger said:
PF isn't over here... it's just HERE. :biggrin:

Be educated... be very educated... :rolleyes:


yea i got it dude.
n i m educated:mad:
 
  • #36
now what's the final answer to my question?
 
  • #37
The engine is silent; what you hear is the driver farting. The sound is entirely dependent upon his diet.
 
  • #38
Danger said:
The engine is silent; what you hear is the driver farting. The sound is entirely dependent upon his diet.

:confused::confused::confused:
how come i didnt think of that? now i know why they call it POTATO-POTATO-POTATO sound:smile::smile::smile:

now anyone serious abt the question?:mad::mad:
 
  • #39
At this point, I doubt it.
If you want 'serious', go back to the first couple of pages where your question was repeatedly answered.
 
  • #40
well actually, only gaming addict understood my question right
no one else did
 
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  • #41
Wrong, pal. We all understood it, and answered to the best of our abilities. For some reason that I can't begin to fathom, you are unwilling to accept those answers. So I really have to ask you... why do you ask a question to which you don't want an answer?
 
  • #42
i got my answer. n i want to get few good explanations about those. so that's why i m askin it.
n yes i do appreciate all of your help, those links really provided me with some good reasons.
 
  • #43
buster said:
those links really provided me with some good reasons.
That might be part of the problem. There are no reasons in science. We strive to answer 'how', but 'why' is a philosophical pursuit.
 
  • #44
buster said:
aaaaaaaaa... what's a YANK?

Also known as "Septic" @ arrse.co.uk
 
  • #45
Danger said:
We strive to answer 'how', but 'why' is a philosophical pursuit.

fair enough. but i didnt ask how or why, i asked which.
now let me eloborate what i asked & what most of u assumed i asked.
i m not talking about the sound that AC makes or the fuel pump makes or any other thing(fans, belts, pulley, gears) attached to the engine makes, these are all the result of running engine. this is what you guys hav been assuming(ofcourse except gaming addict(hehe i m gaming addict too!:-p:-p))
what i have been looking is the source of POTATO-POTATO-POTATO sound (or the farting noise as Mr DANGER suggests), the power stroke(or the CONTROLLED combustion, still i would say it as the explosion of charge regarding the problem), or the exhaust stroke(high pressure gases going out via outlet valve, thus producing a shockwave(as i understand))??
i say it is the 2nd one..
now do i need to get more clear?
and also, i think i have my answer correct with enough explanations
 

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