Motor Trend's review of the 2008 CTS was fairly glowing until it hit this statement:

I heard very similar complaints when, for example, the Lexus ES and RX went from the old school 3.3L V6 to the new GR-series 3.5L w/ direct injection. Though the complaints were not as extreme - they generally just said it sounded louder than the outgoing motor - but not that it transmitted significant vibration back into the pedals and shifter

My observation with my own direct-injected Audi 2.0t is that it's noticeably rougher sounding and feeling than the 1.8t it replaced from the previous generation.

The common denominator here appears to be direct inject in all cases.

So I guess that's just the nature of DI by default, no matter who's using it - the Germans, the Japanese, or the US?

Though the review still makes the overall NVH qualities of the LY7 sound particularly bad. Has anybody else heard this motor yet? How would you describe it?

 

Haven't heard the Caddy, but my DI 3.0 BMW is definitely noisier at start-up than previous BMW 3.0L (E46) that I've owned. It's just for the first minute or so, though. Then it quiets down to near pre-DI levels. I have also noticed that under extreme high temps (sitting in traffic, idling with A/C on high, ambient temps of 100+) it develops a coarse minor vibration (almost like a magic-fingers bed) but only at idle. As soon as you give any gas at all it smooths out. My 04 GTO had this same trait, but much more pronounced. The whole car would start humming and vibrating like crazy. All you had to do to smooth it out was just rest your foot on the accelerator pedal. Very irritating.

 

I've read DI has a rough sound on start up vs. all non-DI engines.

In the '08 STS Does a good job of quieting the DI down from what I've read in reviews. MT said it was quieter than most other DI V6 sedans they have tested. I haven't heard any of them yet myself though.

 

Direct injection technology has worse nvh buy nature (just like diesels by virtue of similar characteristics) Its a natural by-product of the DI combution process.The new CTS has many new "non-Cadillac like features" to minimize the impact on the driver and I wouldn't be surprised if its at least as good as the aforementioned competitors.

 

I guess it's just semantics, but my reading of that review is that the NVH on the 3.6 stood out precisely because the rest of the car was so solid.

As far as the trade off goes, I'll definitely take extra hp and fuel economy for a bit more vibration (then again, my current car has the 3800 S/C, so I'm used to a bit of high end gurgling).

 

Why would the nationality matter?

 

Was that an honest question or were you just looking to get upset about something?

If it was an honest question, here's my honest answer:
It was a generic reference to the wide range of brands with widely different approaches to powertrain design and the fact that all of them seemed to have been unable to quell the negative NVH impact of DI.

 

I.e., no matter which company builds it. The way you wrote it, it wasn't obvious that was the question.

 

Seems to be a problem with DI motors. Anyone read anything about the LNF motors in the Sky or Solstice?

 

It might have something to do with fuel pressure. I know the DI engines in the Sky and Solstice run just under 1000psi. So, if they don't have problems, then I would think it would be related to fuel pressure.

 

Mazda's DI motors (all their current turbo cars) run at approx 1600psi when cold, dropping down to ~900psi when warm. I'm sure that has to do with cold (high) idle as the high pressure pump is purely mechanical.

 

All DI engines are comparatively noisey.

 

How does the combustion in DI differ to the point of causing additional vibration? Later combustion? Higher compression ratio? Higher peak pressures?

I drove an IS350 for a bit, and the only thing I noted was the tick,tick,tick of the injectors. It kinda sounded almost solid lifter-like to me, only a bit less noisy, of course. It did seem to quiet down after the car warmed up some, but still noticeable. The 306hp did have a way of taking your mind off that, though.

 

Threxx, you'll be happy to hear that the October '07 copy of MT has a short bit in the rumors section where they mention that the poor NVH of the new 3.6 is due to some design inadequacy.

Of course, we have no idea how true this is or whether the design issue is shared by other DI engines, since there are no details in the MT bit.

 

Well in the other thread I mentioned I test drove the non-DI 3.6 and it seemed normal in terms of NVH. I'd say roughly on par if not slightly better than the 335i I drove.

They didn't have a DI model for me to check out though.