Big Spool sound diffrence GT30R vs. GT35R
12-04-2007, 04:44 PM
#21
Originally Posted by slimjim8201,Dec 4 2007, 05:36 PM
Then explain your reasoning. Everyone else is throwing ideas out, some more eductated than others. What makes your ideas so special that you feel they don't deserve to be shared until this thread "matures"? You started the thread, why do YOU think there are differences in turbo sounds with different turbo designs?
The pitch of the sound coming from a turbocharger is just about completely dictated by the rotational speed. The faster it spins, the higher the pitch. Period.
A large turbocharger operating at low pressure will be spinning relatively slowly. The sound of fast moving air/wastegate noise, exhaust may far outweigh sound generated by the spinning turbo. A small turbocharger operating at high pressure will be spinning relatively quickly. This may come through as a very high pitched whistling.
Here's a wrench in the gears...
The upper limit of the audible range of human hearing is about 20,000 Hz or 20K cycles per second. If a turbocharger compressor wheel is comprised of 20 vanes, and the wheel is spinning at 120,000 RPM (which is 2,000 rotations per second), a blade will pass the compressor housing cut-water at a frequency of 40,000 Hz. That is, one single blade will pass the most restrictive part of the housing (the location of a massive pressure stagnation point and more than likely, a few shock waves) at a frequency of 40,000 times per second. Thats two times higher than our ears can distingish, therefore...we can't even hear it.
The pitch of the sound coming from a turbocharger is just about completely dictated by the rotational speed. The faster it spins, the higher the pitch. Period.
A large turbocharger operating at low pressure will be spinning relatively slowly. The sound of fast moving air/wastegate noise, exhaust may far outweigh sound generated by the spinning turbo. A small turbocharger operating at high pressure will be spinning relatively quickly. This may come through as a very high pitched whistling.
Here's a wrench in the gears...
The upper limit of the audible range of human hearing is about 20,000 Hz or 20K cycles per second. If a turbocharger compressor wheel is comprised of 20 vanes, and the wheel is spinning at 120,000 RPM (which is 2,000 rotations per second), a blade will pass the compressor housing cut-water at a frequency of 40,000 Hz. That is, one single blade will pass the most restrictive part of the housing (the location of a massive pressure stagnation point and more than likely, a few shock waves) at a frequency of 40,000 times per second. Thats two times higher than our ears can distingish, therefore...we can't even hear it.
I just said after I get more info I will share what I think. We have enough poeple on car forums that run there mouth before they research something out.
WITH YOUR PERMISSION, can I do a little research and gather some information before I start running my mouth once I gather some information and know a little more what I am talking about?
J. R.
PS. Thanks for your contribution. I see good theory with what you have described. So then maybe the reason why we hear the whistle more with non-ball bearing turbo's is because it stays with-in the frequency our ears can hear for longer as it spools slower maybe?
12-04-2007, 05:22 PM
#22
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Originally Posted by flexer,Dec 4 2007, 09:44 PM
PS. Thanks for your contribution. I see good theory with what you have described. So then maybe the reason why we hear the whistle more with non-ball bearing turbo's is because it stays with-in the frequency our ears can hear for longer as it spools slower maybe?
12-04-2007, 06:29 PM
#23
Originally Posted by slimjim8201,Dec 4 2007, 06:22 PM
There's more to it... The rotational speed only affects the sound pitch, not the sounds itself. Think of it this way, a clarinet and a trumpet can both play the same note (the same pitch), but they sound very different. Same thing with the bearings. Ball-bearings create lower friction than standard journal bearings and this will lead to different sounds properties as well.
the pitch of the sound coming from a turbocharger is just about completely dictated by the rotational speed.
So we are saying that the speed of the turbines dictates the frequency, which is c/lamda or wavelength.
So the pitch of the whine is that frequency. When you look at the sound differences of two instruments on a oscilloscope you can see that while the same note will have the same frequency's there amplitudes are different giving them different distinctive sounds.
In a turbo we are suggesting that this comes from
1. Size of wheels
2. Size of housings
and now 3. ball bearing or non-ball bearing.
This is actually becoming a good discussion.
Do you see why slimjim I haven't posted what I think? Its because I am still learning all the factors here, and getting the whole picture.
But hey if you already know the full picture....well PLEASE don't let me waste my time and everyone else's and just tell us, because from the post above we have some conflicting comments so there is some confusion with this topic.
What have you experienced slimjim?
For me its been:
1. Non ball bearing seems to whistle louder
2. Larger turbo's seem to whistle louder
3. The more boost you run, it seems to whistle louder
J. R.
12-04-2007, 07:16 PM
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Originally Posted by flexer,Dec 4 2007, 11:29 PM
...because from the post above we have some conflicting comments so there is some confusion with this topic.
Of course, all of this is speculation at this point. Some of it is informed speculation, but none of us have proven test results to come to an empirical conclusion.
I'm relying on my engineering expertise for my conclusions. My line of work has me working with fluid dynamics for about 10 hours each day so I'm posting stuff as it pops in my head.
Originally Posted by flexer
For me its been:
1. Non ball bearing seems to whistle louder
2. Larger turbo's seem to whistle louder
3. The more boost you run, it seems to whistle louder
1. Non ball bearing seems to whistle louder
2. Larger turbo's seem to whistle louder
3. The more boost you run, it seems to whistle louder
The more air moving through a compressor will result in more "sound". Higher velocities along pipe walls lead to higher local shear stresses (a large factor in sound generation).
As compressors reach their operating limits (the surge line and the choke line), they become very innefficient and they either spin so fast that the blades stop pushing air or the back pressure (boost) becomes so great that the flow actually reverses and goes the wrong way through the turbo (BAD). Under transient situations turbos operate at points all over their compressor/turbine maps. I'm sure this has something to do with varying turbo sounds, too.
I'm rambling...
12-04-2007, 07:48 PM
#25
Originally Posted by slimjim8201,Dec 4 2007, 08:16 PM
Who's confused? The pitch is mostly dictated by the rotational speed of the turbo. Period. Pitch is just one small part of the overall sound.
Of course, all of this is speculation at this point. Some of it is informed speculation, but none of us have proven test results to come to an empirical conclusion.
I'm relying on my engineering expertise for my conclusions. My line of work has me working with fluid dynamics for about 10 hours each day so I'm posting stuff as it pops in my head.
I don't have enough first hand experience with all of the various turbo-types to know the differences frankly. My guess is the journal bearings will sound different, given their different design and increased friction. A larger turbo is cutting through more air "area" and in general, is moving more air, so it too will sound different. Louder? Maybe... Loudness is another quantifiable entity entirely.
The more air moving through a compressor will result in more "sound". Higher velocities along pipe walls lead to higher local shear stresses (a large factor in sound generation).
As compressors reach their operating limits (the surge line and the choke line), they become very innefficient and they either spin so fast that the blades stop pushing air or the back pressure (boost) becomes so great that the flow actually reverses and goes the wrong way through the turbo (BAD). Under transient situations turbos operate at points all over their compressor/turbine maps. I'm sure this has something to do with varying turbo sounds, too.
I'm rambling...
Of course, all of this is speculation at this point. Some of it is informed speculation, but none of us have proven test results to come to an empirical conclusion.
I'm relying on my engineering expertise for my conclusions. My line of work has me working with fluid dynamics for about 10 hours each day so I'm posting stuff as it pops in my head.
Originally Posted by flexer
For me its been:
1. Non ball bearing seems to whistle louder
2. Larger turbo's seem to whistle louder
3. The more boost you run, it seems to whistle louder
1. Non ball bearing seems to whistle louder
2. Larger turbo's seem to whistle louder
3. The more boost you run, it seems to whistle louder
The more air moving through a compressor will result in more "sound". Higher velocities along pipe walls lead to higher local shear stresses (a large factor in sound generation).
As compressors reach their operating limits (the surge line and the choke line), they become very innefficient and they either spin so fast that the blades stop pushing air or the back pressure (boost) becomes so great that the flow actually reverses and goes the wrong way through the turbo (BAD). Under transient situations turbos operate at points all over their compressor/turbine maps. I'm sure this has something to do with varying turbo sounds, too.
I'm rambling...
When a turbo gets out of its efficiency it doesn't do what you described, but that is off topic of this thread so PM me if you would like to talk about that and we can discuss it between the two of us. A clue to help you just think of a fire hose and a garden hose having the same pressure. You understand fluids well so if you use the garden hose.....and we keep upping the pressure. There will be a point where using the ideal gas law of PV=nRT, raising the pressure will only cause a temperature increase not any more flow because of the restriction cause by the volume of the hose and its surface friction. This is why you hear people say a ___ turbo is only good up to 18 psi then its just a big hair dryer after that. This is the turbo stepping out of its efficiency range. <------ there is WAY more to that topic, but just PM me.
Back on topic. I have personally owned a 12a, 14b, 16G,20G,GT30/71R,R85,T-78,GT40/88R.
These are turbo's I have owned, but with all the cars I tune and play around with among my buddies I am around even more then that list. They all make very different sounds and this peaked my curiosity enough to want to discuss it on the forums.
Slim, I think you and I have a common ground on agreeing with kind of whats going on and what "could" be causing the sound differences. Lets see what idea's others have.
HEY WEIRTECH. Maybe we can get you to chime in now and redeem your comment you posted above.
JUST MESSING WITH YOU AARON!!! be a good sport and smile. I'm a joker. 
J. R.
12-04-2007, 10:33 PM
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12-05-2007, 06:47 AM
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Originally Posted by flexer,Dec 5 2007, 12:48 AM
When a turbo gets out of its efficiency it doesn't do what you described...
Don't make me post a compressor map
12-05-2007, 07:55 AM
#28
Originally Posted by slimjim8201,Dec 5 2007, 07:47 AM
It actually does, but you are right, thats another topic.
Don't make me post a compressor map
Don't make me post a compressor map
I will PM you tonight.
J. R.
12-05-2007, 02:04 PM
#30
My dynos with a GT35R.
w/o headgasket run low boost:
http://www.youtube.com/watch?v=V4PGyOXAtK4
with headgasket high boost:
http://www.youtube.com/watch?v=zSaVSYQqQ0A
As you can hear, the wastegate / exhaust quickly overpowers the sound of the turbo. Buy a turbo based on its dynamic characteristics not how it sounds...
w/o headgasket run low boost:
http://www.youtube.com/watch?v=V4PGyOXAtK4
with headgasket high boost:
http://www.youtube.com/watch?v=zSaVSYQqQ0A
As you can hear, the wastegate / exhaust quickly overpowers the sound of the turbo. Buy a turbo based on its dynamic characteristics not how it sounds...