Thoughts on Engine Sound at High RPM's (kinda long)

Kingbaby · 05-31-2011, 09:14 AM

I'm completely lost...will try and feel/test this out, granted I just have an HR!

Red__Zed · 05-31-2011, 09:18 AM

Out of curiousity, can anyone get a clean recording of a dyno pull? I'd love to run a frequency analysis.

Davey · 05-31-2011, 09:35 AM

Quote:

Originally Posted by RCZ

haha, yeah the car is "rough" pass 4500RPM. You're not going crazy. The way it sounds and the way it feels are two totally different things. No one should appreciate an engine that feels like you're breaking it when you take it up in the rev range...which ours does.

I've put a fair amount of miles on two Z's and I don't think it feels like I'm breaking it at all. I love to rev it up. If you think it sounds like you're breaking it, keep revving it up until you're convinced you're not.

jtsmith1 · 05-31-2011, 09:37 AM

Quote:

Originally Posted by RCZ

haha, yeah the car is "rough" pass 4500RPM. You're not going crazy. The way it sounds and the way it feels are two totally different things. No one should appreciate an engine that feels like you're breaking it when you take it up in the rev range...which ours does.

I don't think its that we're hitting its frequency, it just feels rough. It does it for several thousand RPM and that should tell us its not just resonance, its just that the damn thing vibrates a lot. Be it from the vvel system or more solid engine mounts or what. I've had three types of flywheel on my car and they all made similar vibration at high rpm. You could say the stock fw feels more muffled because it doesnt seem to get transferred into the cabin and chassis as much, but its still there loud and clear.

I had solid transmission mounts installed a while back and the vibration was completely unbearable. At high RPM it felt like the world was ending. I think the best we're going to be able to do is isolate the vibrations as much as we can, maybe we can get some liquid filled mounts like porsche does... that gt3 feels like silk at 9k rpm.

Right! I know its not resonance, if it was then the engine would literally tear itself apart. But as you approach resonance, vibrations increase until you reach resonance, then slowly decrease as you continue passed the resonance frequency.

I'm wondering if the engine is approaching this range, frequency wise, as its rpms are increasing.

Hydraulic mounts would be awesome, as long as they didn't leak, which all do over time.

wstar · 05-31-2011, 12:06 PM

I guess it's subjective whether it sounds/feels like a problem. I'll grant you, to me it sounds like a beast of a machine rampaging out of control, but I guess that's what I expect from that many RPMs in a V6. Doing the math (3.7L V6, 4-cycle), at say 7,000 RPM that engine is exploding a 617cc ball of fuel/air mixture about 350 times per second in a tiny lightweight aluminum machine, and trying to capture rotational mechanical energy from the process. I'm sure some engineering could make it sound/feel sweeter, but c'mon what do you expect?

It never feels to me vibrationally like the engine is tearing itself apart though. It could be that the 7AT's torque convertor damps a lot of the vibration, so that we only get engine-mount vibrations and not transmission-mount vibrations, if everyone who notices this has a 6MT.

Davey · 05-31-2011, 12:38 PM

I drive a manual.

I'm not saying it's silky smooth or anything, I just don't think it's that bad or that it feels like there is an issue. From what I read in the press I was expecting much worse, but I think it's actually a little smoother than the VQ35HR.

But, for a V6 it's pretty damned smooth.

Kingbaby · 05-31-2011, 12:39 PM

Quote:

Originally Posted by Davey

I drive a manual.

I'm not saying it's silky smooth or anything, I just don't think it's that bad or that it feels like there is an issue. From what I read in the press I was expecting much worse, but I think it's actually a little smoother than the VQ35HR.

But, for a V6 it's pretty damned smooth.

this is what I've heard from 350z MT to 370z MT drivers

phelan · 05-31-2011, 12:54 PM

Quote:

Originally Posted by jtsmith1

Right! I know its not resonance, if it was then the engine would literally tear itself apart. But as you approach resonance, vibrations increase until you reach resonance, then slowly decrease as you continue passed the resonance frequency.

I'm wondering if the engine is approaching this range, frequency wise, as its rpms are increasing.

Hydraulic mounts would be awesome, as long as they didn't leak, which all do over time.

I think a design parameter for any automotive engineer in building a new engine is to make sure the resonance frequencies are far, far away from any operating condition. The last thing you need is someone taking their car out, high-revving through the gears on the street, then watch the engine hit resonance and displace itself into the road.

Keep in mind that engines (and most mechanical components on mass produced products for that matter) are built with a high margin of safety. For something mass produced like a car, the margin of safety is typically beyond 1.0, to cover remote and extremely remote probabilities. So even at high RPMs, I doubt we are anywhere near the resonance frequency, or achieving any damaging modal shape on the VHR platform.

RCZ nailed it when he said the engine is just rough. Granted some of the mounts could have dampeners on it to soften the vibrational effects, but then you add weight in a car that really doesn't aim itself to be a smooth driver. That's half the fun of the Z; a simple sports car (or as simple as you can get these days....except for the newfangled SRM thingy).

Considering your theory about the flywheel - yes, a heavier one will act as a dampener and reduce the vibration in the transmission. But consider the mass of the flywheel against the amount of force acting on it. To get an appreciable level of reduction will require the flywheel to much more mass than it is worth performance-wise. Do the simulation in MATLAB using a maximum level force input based on the power output of the engine at high-RPM, and you'll see it.

jtsmith1 · 05-31-2011, 04:56 PM

Quote:

Originally Posted by phelan

RCZ nailed it when he said the engine is just rough.

Thats kind of like saying "Because I said so." Something (or a combination of things) is causing this.

I am not saying that resonance is an issues here, I understand that it is NOT the issue. I simply gave some background info on vibrations to help others understand the idea of how rpms (frequencies) can excite materials and mass systems, to help explain what I feel could be an reason for the sound/feel at high RPM's.

I understand the Safety Factor is not identical to 1 and that there is some "overengineering" to ensure there arent any issues (not like this is a fighter aircraft where weight is super critical). However, this is not beneficial for the company from a cost standpoint, so I imagine using a SF much higher than 1 is not a best practice they use often.

I am actually not very familiar with MATLAB, never really used it much, but I would be interested in seeing something showing how an increase in flywheel mass effects the power output.

Red__Zed · 05-31-2011, 05:09 PM

Knowing MATLAB is a really important skill if you want to stay in engineering

Another thing to consider is the possibility of resonance of subsystems. There will always be resonance in a an engine at certain RPMs, even if it is not catastrophic.

jtsmith1 · 05-31-2011, 05:23 PM

Quote:

Originally Posted by Red__Zed

Knowing MATLAB is a really important skill if you want to stay in engineering

Graduated without using it and I dont use it at my current job (nor does anyone else), so I have never really played with it. Maybe I'll start tinkering around with it.

If the system does reach resonance and the engine is held at that state for an extended period of time, there will be failure. However, quickly reaching that frequency and quickly moving past it would not be as much of a worry.

I guess this is not as big of an issue for a lot of people on here, I thought everybody was turned off by the sound/feel at high RPM's.

fuct · 05-31-2011, 05:29 PM

drive an inline 6 (2jz) for seven years then jump into a 370Z and the engine feels/sounds like a truck!

Red__Zed · 05-31-2011, 05:49 PM

I guess we will have to wait for the SAE whitepapers before we can evaluate much further.

I do know for sure the that f/2 harmonic is increased significantly in the 3.7 over previous iterations, due to the changes in the intake manifold/collector.

Red__Zed · 05-31-2011, 05:50 PM

Quote:

Originally Posted by fuct

drive an inline 6 (2jz) for seven years then jump into a 370Z and the engine feels/sounds like a truck!

werd. try coming from an F20C and a K20

jtsmith1 · 05-31-2011, 06:16 PM

As much as I hate to admit it, I came most recently from a b16a2 Haha. College car.

05-31-2011, 12:06 PM	#20 (permalink)
wstar A True Z Fanatic Join Date: Mar 2009 Location: Houston, TX Posts: 4,024 Drives: too slow Rep Power: 3594	I guess it's subjective whether it sounds/feels like a problem. I'll grant you, to me it sounds like a beast of a machine rampaging out of control, but I guess that's what I expect from that many RPMs in a V6. Doing the math (3.7L V6, 4-cycle), at say 7,000 RPM that engine is exploding a 617cc ball of fuel/air mixture about 350 times per second in a tiny lightweight aluminum machine, and trying to capture rotational mechanical energy from the process. I'm sure some engineering could make it sound/feel sweeter, but c'mon what do you expect? It never feels to me vibrationally like the engine is tearing itself apart though. It could be that the 7AT's torque convertor damps a lot of the vibration, so that we only get engine-mount vibrations and not transmission-mount vibrations, if everyone who notices this has a 6MT. __________________ 7AT Track Car! Journal thread / Car setup details

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05-31-2011, 09:18 AM	#17 (permalink)
Red__Zed A True Z Fanatic Join Date: Jul 2010 Location: window seat Posts: 28,940 Drives: Mostly on two wheels Rep Power: 120	Out of curiousity, can anyone get a clean recording of a dyno pull? I'd love to run a frequency analysis.

05-31-2011, 12:38 PM	#21 (permalink)
Davey A True Z Fanatic Join Date: Apr 2011 Location: Indiana Posts: 3,766 Drives: '15 NISMO 6MT Rep Power: 117171	I drive a manual. I'm not saying it's silky smooth or anything, I just don't think it's that bad or that it feels like there is an issue. From what I read in the press I was expecting much worse, but I think it's actually a little smoother than the VQ35HR. But, for a V6 it's pretty damned smooth.

05-31-2011, 05:09 PM	#25 (permalink)
Red__Zed A True Z Fanatic Join Date: Jul 2010 Location: window seat Posts: 28,940 Drives: Mostly on two wheels Rep Power: 120	Knowing MATLAB is a really important skill if you want to stay in engineering Another thing to consider is the possibility of resonance of subsystems. There will always be resonance in a an engine at certain RPMs, even if it is not catastrophic.

05-31-2011, 05:29 PM	#27 (permalink)
fuct A True Z Fanatic Join Date: May 2009 Location: Sugar Land Posts: 3,692 Drives: 97' Ranger :) Rep Power: 24	drive an inline 6 (2jz) for seven years then jump into a 370Z and the engine feels/sounds like a truck!

05-31-2011, 05:49 PM	#28 (permalink)
Red__Zed A True Z Fanatic Join Date: Jul 2010 Location: window seat Posts: 28,940 Drives: Mostly on two wheels Rep Power: 120	I guess we will have to wait for the SAE whitepapers before we can evaluate much further. I do know for sure the that f/2 harmonic is increased significantly in the 3.7 over previous iterations, due to the changes in the intake manifold/collector.

05-31-2011, 06:16 PM	#30 (permalink)
jtsmith1 Base Member Join Date: Apr 2011 Location: OH Posts: 81 Drives: 2009 370z Rep Power: 14	As much as I hate to admit it, I came most recently from a b16a2 Haha. College car.