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I been building and racing cars for 20+ years now, long before the internet bench racers came around. Since many fail to acknowledge even the basic principals of engine functions I'll spell it out:
Engine breathing 101
An engine is essentially a big air pump. The idea behind a CAI or any type of better breathing filter is to allow the engine to breath more deeply, removing restrictions allows a higher volume of air which in theory is cooler and more dense, this cooler denser air has more oxygen in it (especially when the vehicle is in motion and air gets rammed in at a higher rate), as we know the more oxygen you feed a fire the more potent the fire, the more potent the fire the higher the pressure is in the cylinders, the higher the pressure goes up the more power an engine makes. As you restrict the oxygen the fire becomes less potent, the pressure descreases and the power levels subside, restrict it entirely and the fire goes out (that's when your pushing).
Therefore if we control the amount of oxygen in the air coming into the cylinders we control how much power the engine makes, to a certain degree of course because we haven't even begun to talk about timing, fuel, etc. In addition to that a cooler, denser charge will also supress detonation which allows for more timing advance, more fuel delivery, more power.
Now at some point the fire will only be so strong regardless of the amount of oxygen but the principal of better output due to cooler, denser even faster moving air can make small improvements to power output, period. I'm not here to argue and say your going to get gobs of horsepower by changing the intake, I'm saying you'll see a modest increase over the factory design, which in itself is driven by cost and the need to cater to the masses. The baffels and restrictions and bends and filters are all picked to provide the necessary power levels to achieve the engineers goals, which are to run the engine safely, provide optimum fuel economy and make it quiet, sometimes they make it so quiet that they put "noise pipes" on to add to the "experience" (VW, Ford, they all do it, I've removed several).
It doesn't make the turbo make more boost, it makes the turbo more efficient, now here's where it starts to get a bit muddy:
Why do you think your car runs better when it's 50 degrees and cold outside vs when it's a 100 degrees and sweltering? thoughts?
Here is what Gale Banks says, "It's all about airflow. Airflow helps engines make power in many ways, but it is also true that the more air you can flow through an engine, the more oxygen that will be available for burning fuel. More oxygen means more fuel can be burned, and that means more power."
I'd say that guy really knows his 'ish. It's also about temperature and pressure, change those variables and even at the same boost levels the output you get will be drastically different.
So why does your car run better with a cooler intake charge vs a hotter intake charge (or a more restrictive one)?
Well here's why:
The general rule is that for every 10º of temperature drop, the density (and oxygen content) increases about 1 to 1.8 percent. Similarly, power increases by an equal amount. If you have a temperature drop of 50 degrees for example (100 vs 50, I live in FL I see both those temps) you can potentially effect power by somewhere around 5 to 9 percent to the positive as temps drop. Lets apply some simple math to that:
365hp x 1.8% = 6.57HP increase per 10 degrees of temperature drop, drop 50 degrees and your car will make approximately 32hp more (5 x 6.5) at 50 degrees then it will at 100 degrees, and that's leaving the boost levels exactly the same. Now if you really want it to get ugly start figuring in pressure levels at different atmospheres, thats why your car runs like crap at 5000 feet, there is less oxygen in the air, less pressure, less density it all equals less power.
So how does this come back to a Cold Air kit. Using our simple math from above many have seen around a 10 degree drop in IAT's using a well designed cold air intake system, as we have discoverd that is about a 6.5hp increase for our application. Now as the volume of air goes up (the ram effect and using more surface area on the filter) the IAT's can drop even further, lets say 15 degrees, now your making about 9.2hp more (again for our application) just by putting an effective intake system on that can both decrease temps and increase volume making the air more oxygen rich, which we now know effects performance (without effecting boost levels). Oddly enough that CAI we are all discussing makes about 9hp give or take temp, pressure, etc; and after doing the math, seems to be just about spot on. With an increase in volume, cooler charge, more oxygen, you get more power.
...I'll retire my soap box now
Wait what? ARE YOU GUYS SAYING I SHOULD HAVE LEFT MY STOCK INTAKE ON THIS WHOLE TIME?
Damn, I wish I had known this from the beginning, I could have moar powa.
Gosh, now I need to find a stock air box now.
And YES, that is a SHO oil cap I am currently using
According to the Caddy Forums (I've been looking to buy a V) they put down 34rwhp with CAI alone, and another 28 with the tune. I go by the results.
There are tons of threads out there with guys like us doing the testing, running there stuff at the track and tuning it with a dyno to see what does and doesn't work. I've had 25+ cars over the past 10 years (I go thru them about every 8-10 months, sometimes faster). I don't expect to have the SHO much more then a year or two. I'll tinker with it like I do everything else, squeeze what I can out of it, enjoy it for awhile and then I'll get bored and go get the next toy. The V and the M5 are very high on the list.
Here is the dyno chart from all 3 runs. Stock, CAI, CAI+Tune. Most of the gain was actually from the intake only without the tune. Notice the gains all across the RPM range not just peak, solid 20+HP EVERYWHERE, and not just HP Torque is up 20+ as well.
Now to be fair a supercharged application does benefit a bit more then a Turbo application. And I think we are all in agreement on the SHO your really not going to get a whole lot, I would guess 5-10hp. My 04 Cobra was S/C and it gained almost 30+hp with just a K&N CAI vs the stock box. All the Turbo cars I've had haven't shown near that improvement (SRT-4, Saab, SHO), all my S/C cars did very well (Roush S3, 04 Cobra). My NA cars have had mixed results (4 other NA Mustangs, GTO, R32, CC, misc Lincolns some sprayed to the hilt, etc).
It's my own personal preference, I try not to leave any power on the table, yes I'm the guy that will spend $400 to gain 10HP, again that's just me, not for everyone. But sometimes it's the little things that put you a fender in front of the next guy. I'm a pretty competitive person and have done a lot of racing, many times it was the little tweaks with a couple HP here and there that made the difference of winning or losing and I really hate to lose...
One fella found it for less than $250. I posted $400 cos of what they would want you to sell it for. No one is going to sell it for that much (I hope). At my shop, I'd sell it for $289.99 now. Same as my diesel ones I sell. I wouldn't rape anyone for $400, that's crazy. But like others have said, some will pay for it, some will not. I, too, welcome the aftermarket part world with open arms, not matter what it may be. As long as the don't make those damn Lambo doors, we'll be alright.
