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

So most people have spoke of how the sound of the VQ37VHR becomes less desirable at higher RPM's. After spending some time in my vehicle, I am curious as to what is actually causing this.

It seems to me that some of it may be related to the balancing of the engine. I feel a bit more vibrations in the higher RPM's, which I think could be a potential source of this noise.

Some quick vibrations 101:

From a purely fundamental vibrations standpoint, everything has a resonance frequency, including the overall "system" under the hood, or the engine. One main design parameter to consider when designing an engine is the overall RPM range it is intented to operate within (which, at any given RPM, corresponds to a certain frequency). Once you understand the operating range, the next thing to consider is how to balance the engine to ensure you will not run into a condition that may result in resonance.

Resonance is a term used to describe a state at which a "system" has been excited by a frequency that is equivalent to that "systems" natural frequency. When this happens, things get nasty in a hurry (serious deflections and movement to the point of catastrophic failure). Think of suspension bridges swaying like crazy during earthquakes.

So in order to keep this from happening with an engine, you add weight here and there to change the "systems" natural frequency, balancing the engine. This is also used to help reduce the overall torques felt within the components of the engine, so they dont end up translating into the drivers seat. Also, a flywheel is used as a damper, essentially absorping some of the vibrations, so you don't feel them when you are sitting in your car.

So here is what I am curious to know: did Nissan miss the mark with this? Did they sacrifice a smoother operating engine for a lighter one?

If so, I think some of the noise we may be hearing is due to the vibrations of the materials at higher rpms. This is good and bad. The bad part is, that means there was more room for improvement on the design of the overall engine. The good news is, I think this could be improved on significantly with the addition of a heavier flywheel.

Yep, thats right, a heavier flywheel. While I have no real world experience with this, I believe moving to a light weight flywheel would actually cause this situation to get worse, while increasing the weight of the flywheel would reduce the vibrations of the engine at higher RPM's and potentially provide a smoother feeling and better souding engine.

Any thoughts?

You blew my mind away, but nice theory. Test it out :)

you sound like you either had a strong emphasis in mechanical engineering or physics in your field of study.

Just finished my BSME, haha. Wanted to explain it a little more in depth to provoke thoughts of others on the board.

I would love to test it out, but just dont have the time to do it. However, I would be interested in hearing some feedback from others who may have used a light weight flywheel option (not sure if anyone is doing this with their 370's).

If it can be confirmed that a lighter flywheel causes the problem to get worse, than it stands to reason that using a heavier flywheel (one way to overbalance an engine) would reduce vibration and sound.

O.k. - the V-6 is always unbalanced, firing-wise correct (2 on one bank, 1 on the other or similar). This is a second order rocking motion - correct?. I guess that rotationally a V-6 can be balanced (first order -?). Are these both torque (rpm) sensitive? Would a weighted fly-wheel do anything for non-rotational ( other than first order) unbalanced?

I'm an EE so excuse my lack of knowledge.

I don't think the roughness/harshness is an issue with resonance TBH.

I think it mostly has to do with the fact that the engine isn't balanced. You almost never see a v6 revving up this high, especially not one with this old of a design.
It's really not possible to have a smooth, high-revving V6, and our engine just helps demonstrate it.


EDIT:

Yes, a heavier flywheel would likely smooth things out, but that's not a performance knock I'd be willing to take...

Especially since it likely would only make a VERY small difference...

Keep in mind the VVEL is changing lift and duration and only maxes them out in the higher RPMs and at high load. Changing the cam profile like this is going to affect the sound of the engine. At lower rpm and load, the engine acts like it has a mild cam, and at higher rpm and load it's more of a performance cam.

Not an expert in this area either, but I do believe almost any second or higher order vibrations can probably be neglected due to significantly lower magnitudes, cannot say this for sure though.

As far as the firing order, I never really put much thought into it. It seems that it would also be a function of RPM due to the change in momentum of the masses. I guess a good set of mounts (essentially dampers) and a properly balanced crank would be key here.

Not sure what you mean about non rotational unbalanced? The flywheel can essentially act as a bandaid, covering up some imbalances in the engine and absorbing some of those vibrations. Obviously, from a performance standpoint, we would like to reduce the mass of any rotational parts, but at what cost? I think a heavier flywheel would "overbalance" the engine, reducing any first order vibrations and probably minimizing any higher order vibrations as well.

Again, not an expert in vibrations, just have a basic undestanding. I do have some software on my laptop that we used in school to analyze engine parameters during design, such as balancing. If I knew every detail about the engine, such as bore, stroke, all the masses (major components such as wrist pins, piston, conrod, and crank), I could do a little analysis and see what sized flywheel provided the smoothest torque output and minimized vibrations. Question is, how much heavier would this be and what would the performance trade off be?

The engine noise or vibration isn't even bad, just adds to the excitement.

I suggest you go to a local track/car meet/pm local members on here...

VQ37VHR or any VQ to me sounds even better at higher RPM! Some are expecting some magical tone when adding bolt-ons! Doesn't happen that way, you don't get power without lose comfort. Now that exhaust note at higher RPM's to some is bliss....I think playing this out in theory is pointless! I'm sure Nissan has put countless hours into this.

The VQ37VHR out in the 6K+ RPM range is music to my ears, no idea what you're talking about :) I wish I had a camcorder that could capture the sound better on dyno runs.

Yeah, I've said before, I read the reviews of the car being "harsh" and "noisy" and "unrefined" in the higher RPM ranges and I just don't see it to any degree I could care about. What's to complain about, with a V6 spinning at 7500 RPM? :driving:

Either I am missing the sarcasm boat or there is a significant difference between members definition of refined. My Z is far from it at high rpm's, especially off throttle. Maybe some are just not familiar enough with the topic to know it when they hear it.

Next time you guys are driving, rev up to redline and let your foot of the gas, allowing the engine to spin down by itself and see what you think.

Again, for some, this may not be an issue.

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.

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

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

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. :roflpuke2:

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 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.

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 :tup:

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.

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.

Knowing MATLAB is a really important skill if you want to stay in engineering :rofl2:

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.

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.

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

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.

werd. try coming from an F20C and a K20:roflpuke2:

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

I'd actually love to see something from all the people who don't think the engine is rough--what engines are you coming from?

EK civic or swap?

...duh?

Are you an aerospace engineer?

I came from a 2001 maxima (3.0L version of the VQ) and it was MUCH smoother at higher rpms. Although it only revs to 6000-6500 (cant remember exactly). I have also driven a Cayman S, which is much smoother as well.

Glad I'm not the only one who thinks this engine vibrates like crazy. Kinda freaked me out the first time.

I came from an LS1 before this car.

I came from a 2000 Maxima, but also had a 2010 for a few months. :tup:

VQ35DE

I remember the first few weeks driving it [after breakin] it feeling rough at 5,000+ RPM's. I must have got used to it after a while because it doesn't seem too bad anymore. :icon17:

I usually have other things running through my mind when I'm approaching redline.

No, I work in the aerospace industry and I am a mechanical engineer, haha. I work on a team that designs jet engines, I do mostly mechanical/air flow stuff. Newly graduated though, so Im still wet behing the ears. Worked on airplanes such as the F-16 and the KC-135 for the past 8+ years though.

Zed, I had an EM1 civic. Needed something for college, sold my 240's so I wouldnt keep dumping money into them and got something practical, but it still needed to be a little fun.

My wifes TL also has a v6, although smaller, is much more refined and no vibrations at higher RPM's. That is to be expected with a nicer/luxury style vehicle, but can we learn something from those platforms and apply it to ours?

A few have spoke of the smoothness of the Porche engines. For a flat six (horizontally opposed), alot of the dynamic forces from one bank are cancelled out by the other. If you think about how the engine operates, this is pretty easy to understand. Unfortunately, that is not the case with our V shaped engine.

Tranceformer, did you notice anything significant when switching over to your JWT flywheel?

So you're a compressible fluids engineer? Do you use ANSYS for CFD analysis?

And yes, there are multiple reports that a lighter flywheel increases vibration in the crankshaft. That much should be obvious. While it is tempting to consider the easy "oh just make the flywheel" heavier, however, don't forget that a dampener does exactly that - it DAMPENS the response. The full magnitude of the force still must be transmitted, but now it's over a greater time T. So basically...all of the responsiveness of the engine is now thrown out the window.