Does this mod ever give a measurable increase in power?
tl;dr: yes, sometimes it works well. But...
Your picture is a good illustration of some of the problems with just saying "cold air intake" and expecting that to mean the same thing to all people. Let's break down the pieces of the puzzle and talk about how those might help or hurt:
- Filter: notice that the filter in the picture is not a panel filter as many of us have in the airbox. If that filter is less restrictive than stock, that will certainly impede the intake's job of getting air molecules into the system less. However, is it still filtering out hazards to the motor? Is it an oiled filter? Will that oil get onto the mass airflow sensor?
- Piping: the actual path that the air takes is definitely important. Is this piping better at thermal isolation? The engine bay is hot and hot intake air means less performance. Is the piping less restrictive? Does the air flow better? Does it flow too well (causing a lean condition)?
- Location: the intake in the picture appears to be a short ram intake. That means that it only reaches to the standard location of the airbox. Will it be drawing air directly from the hot engine bay? Or is there another path for cooler air to reach the intake? Would it get cooler air sucking from directly in the wheel well? Of course, then you run the risk of sucking up water in a heavy rain....
In theory, the engine is an air pump. If the intake can reduce restrictions and pumping losses, it's all good, right? Unfortunately, even in the theoretical world, freeing the intake isn't going to solve a restrictive exhaust (can't get the air out as fast as we can get it in).
Let's talk two practical examples using my cars:
- 1997 Acura Integra NA 4 cylinder. I tried two different cold air intakes on that car. Both of them seemed to make the car happier (subjective assessment based on a nicer sound). However, the power increases weren't really significant until I had replaced the headers and the exhaust system with stainless steel. The car sounded great, revved well and had a lot more pickup. There was every reason to believe that I'd removed several restrictions on a car that had originally prioritized quiet over fun. However, I'd also removed a lot of weight of metal by switching to stainless (those iron headers were heavy). In this case, the CAI was part of the picture but not the biggest part.
- 2004 Subaru WRX Turbo 4 cylinder. This car has a reputation for ignoring CAI changes without a retune. The ECU simply recalibrates to match the increase in airflow, resulting in no increase in power. There's also a risk of damage to the MAF using oiled filters. There's also the reality that I don't need to worry about the same intake restrictions that I had on the Acura: I'm not just hoping air wanders into the engine with a turbo in the mix! With this car, the recommended change is a less restrictive panel filter that drops in place of the stock.
So, where does this leave us?
- A CAI has a good chance of sounding cooler than a stock intake. It will definitely be louder.
- A CAI will reduce restrictions in the intake path. That might lead to more power out of the box. It might not. It might lead to engine damage. Caveat emptor.
- A CAI may increase risk of water ingestion. This may lead to hydrolock (a broken engine and many tears).
In short, like all things car related, it depends. On an older car with a weedy intake and hot under hood temperatures, I would certainly try a CAI. On a modern car, I don't bother.