CAI benefits
 

Not an expert here, but trying to understand the benefits of the CAI that is stirring up lots of interest. Not picking on AFE here, as it seems quite similar to the others. Apologies if it isn't. The attached chart is from the AFE website, for a 4.4 X5. There is no dyno result for the 3.0, just a claim regarding more air flow.

How does an engine benefit from more airflow strictly at the filter? If the filter is overly restrictive, then I get it. I would think, though, that the engine design has the intake system, engine flow characteristics, and exhaust system balanced to a certain extent. So, wouldn't an exhaust, a cam, and probably engine software be required to get any significant benefits from just a less restrictive filter? Shouldn't airflow matter more at high rpm?

What the chart shows for the AFE CAI (and I will take it as read, no need to debate dyno accuracy) is that the flow characteristics are changed, not necessarily improved. The 10 hp CAI gain is over a very narrow 200 rpm band, around 3200 rpm and even that is being generous. There is a trade off in that there is a similar drop at 5300 rpm, but that is likely inconsequential. There is, however, significantly less torque/hp with the CAI installed, from 2100 to 2700 rpm. There is more torque with the CAI installed, from idle to 2100 rpm. Is the gain below 2100 rpm worth the loss above 2100? The peaks are similar, but the CAI has a narrower band, which would seem to make the engine very responsive just off idle, trading off for the associated losses further up the rev range.

Is the auto trans not calibrated to the torque characteristics of the engine? Does this have any impact on drivability?

I don't see any warranty issues, unless it is with the check engine light that the web site mentions is sometimes a problem. The filter is mounted high up, so I don't think water is a problem. The filter looks very well made. There are no measures for how effective it is at filtering (in microns), but I presume that would vary with how much it is clogged, similar to other cloth filters with oil that get more effective once they are dirty. If I dusted the engine, I know that would be on my dime and not on BMW's, but that doesn't seem likely if it is properly installed.

Finally, I see lots of comments about the sound, and I understand the attraction of a moan of an intake system. Is that the primary reason for a CAI?

What am I missing? All thoughts welcome.

Nobody has an opinion?

Just looking at the chart, HP/TQ gain is so minimal and with the heavy weight of the X5 I just think paying $300+ for the CAI is not worth it.

I have noticed this with myself as well as other drivers: having something like a CAI allows you to only hear it with generous application of throtte. You are correct that the primary attration for most modders is the pleasant sound although the justification might be otherwise. The point is that I took off the intake on my Prelude because I wanted to hear it my right foot got heavier. If you want to hear the intake, you're gonna have to give it more gas (literally). I am with Eugene, just can't justify the sound with the cost of $300 and potential increase in fuel consumption.

I find it interesting that the CAI produced greater in lower rpm. With I4's, there is always a loss down low, which is made up in the upper midrange and primarily in the upper rpm. I4's: the CAI yields more power closer to the peak cylinder pressure, which seems logical. Here it is not so. Any thoughts.

My take...but no expert either.
 

JCL I understand your point. CAI, even when used in conjunction with a free-flowing exhaust, won't give you any noticeable performance gain on an X5 but it's one of the first mods that an enthusiast will do, to any car. First and foremost it looks a heck of a lot better than any stock airbox so it dresses up underneath the hood a bit. Second, yes you do hear the intake sound but is that the only reason? Probably not. Third, my fuel economy has improved a bit and I don't think my driving habit's changed. So IMHO there are some merits for having CAI. Now is the cost justified? That depends. There are some intakes that cost over $1000 and some people still buy them.