In my original post, I briefly mentioned the engine smoothness (or lack thereof) on the current G35 which I test drove.

I realize that the new VQ is supposed to have specs that reduce NVH but I wonder if it will be as smooth as the older Maximas and 300Z's were. I haven't driven any VQ's since probably 1988.

Does anyone know what makes the current VQ not as smooth as the older Maxima engines?

Is it a function of timing BELTS vs CHAINS or did they stop using balancing shafts?

Any info would be greatly appreciated.

 

+1. I'm not sure where this so-called smoothness originates, but it sure does not originate from the engine bay in my G. Yes it's far from rough, but it certainly is not the smoothest running motor either - Constant vibrations via the shifter, steering wheel, dashboard and pedals. The IS, Acura and BMW are seem smoother IMO.

But as you said that may have changed for '07.

 

As a general rule of thumb, the more horsepower and compression an engine has, the harder it is for it to be smooth/er.

 

Was smoothness compromised by the cylinder bore increase when the VQ grew from 3.0 to 3.5?

 

Smoothness has to do a lot with the increase from 3.0L to 3.5L like Jspeed said. The maximum displacement for optimal smoothness for a I4 is 2.0L, V6/I6 is 3.0L and V8 is 4.0L, etc. Any larger and you'll lose some smoothness since they they have to increase the bore or the stroke. Increasing either will decrease smoothness. That's why you noticed BMW I6 is @ 3.0L, Acura TSX is @ 2.0L, old SR20 is 2.0L.

 

A V6 by nature lacks secondary balance. V6 was a no-no in the old days, it was either I6 or V8. I4's and V6's need counter balance shafts to make them smoother, but that adds weight and complexity. However, even Lexus and MB have gone to V6. It's a shame....

 

Guys, at the risk being flamed,......hold on a sec......

<.......Mr. Ryte puts on his flame suit......>

Ok, let's think about this:
How many of you actually do R&D/design/tests on engines and vehicles on a daily basis? All these responses about engine size and design for optimum smoothness is interesting, but don't you guys think that these automotive engineers came across these issues and addressed them?

Right now, no one here on the forum has even driven a Nissan/Infiniti with the new engine in it, I can't see how anyone can give an accurate assessment on it.

 

Me. And, I totally agree with what you've said. I'm sure they have made lots of efforts to ensure a smooth, NVH free engine. Just wait to drive it and judge for yourself.

 

Your logic assumes that the extensive R&D done by the Nissan engineers would iron out any engine smoothness issues. However, that doesn't explain the fact that the VQ35 lost some smoothness from the VQ30. The engineers have many agendas to fulfill. Besides smoothness, they are interested in extracting more power from the engines while minimizing cost.

If you do any amount of research on cylinder arrangement vs. running balance, you will quickly realize that an inline 6 indeed is smoother than a V6, all else being equal (e.g. cam profile, build tolerance, displacement, etc.). Companies went from I6 to V6 for packaging reasons. It's simply easier to fit a V6 (almost 50% shorter than an equivalent I6) into modern cars with packed engine bays.

 

IIRC, a major design objective for the new VQ35HR was increased smoothness, I remember reading it in an Infiniti press release. Besides, like the VQ is so terrible.

 

My logic is that when people start claiming that one engine has problem and is better/worse than its predecessor with nothing more than subjective feedback then I think that's being a little presumptuous. The VQ has been heralded as one of the best V6's ever made by many in the automotive press. Each generation surpassed the previous one and thus the VQ has been on Ward's top engine list for the longest time so Nissan must be doing something right.


Besides, how does one actually measure/quantify engine smoothness?

That part I'm familiar with. No engine design is perfect and each has its pros and cons. That said, again I ask-wouldn't the design guys thought of appropriate NVH dampeners to minimize the harshness to some degree?

 

Engine smoothness is related to many factors, but balance is one of the keys. How well an engine is balanced is mostly determined by its basic configuration including the number of cylinders, how they are arranged (v, inline, etc), the angle in between the banks (60 deg, 90 deg, 180 deg, etc). Certain configurations are inherently much better balanced. The best are the inline 6, the 60 deg v-12, and the 90 deg v-8. The VQ engine is a 60 deg v-6 which is a much smoother design than the 90 deg v-6. For more details see the attached link.

http://www.answers.com/topic/engine-balance

 

No need to over-interpret my post. I didn't say the VQ35 was bad. I'm sure the HR's is more refined, which suggests Nissan recognized the increased NVH when the VQ grew from 3.0 to 3.5.

 

I don't think anyone criticized the VQ35 for being worse than the 30. Overall it's an improvement. We were just looking at the NVH aspect.
for NVH? by feel
Yes, they did, but that's not the point some of us were trying to make. Engineers work with all sorts of constraints. When looking at the whole picture, one could argue either for the V6 or I6. V6 holds the advantage for packaging and I6 has better smoothness. The engineers made conscious compromises. No one is saying that they didn't do their job.

 

++1 ^