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

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.

wstar

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.

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phelan

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.

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jtsmith1

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.