Back when I first graduated from college, I bought a 2001 MX-5 to celebrate my leaving of classrooms behind forever. It was a wonderful car and lived up to every bit of hype that has since made the Miata the so-called “answer to everything”. But just like every other Miata that came before it, the power of the car left quite a lot to be desired.
So off to the forums I went to find the best recommendations for easy mods to give my car that extra bit of oomph I so desperately wanted.* One of the first and most repeated recommendations was a cold air intake (CAI) to replace the stock air box and filter. CAIs are of course available from almost every aftermarket parts manufacturer, some reasonably priced and some that would break the bank.
The concept is simple: taking your stock airbox and traditional air filter out of the car and replacing it with a higher flow cone (or pod) filter that is positioned every so slightly closer to the outskirts of your engine bay will promote a more consistent draw of colder air into the engine. Cold air of course is more dense than warmer air, bringing in more oxygen molecules to the combustion process in the engine and resulting in a more powerful explosion of compressed fuel and air.
Sounds great, right? After all, handfuls of forum dwellers claimed that CAIs added 15+ hp to their Miatas. But 15 more ponies was nearly a 10% increase power… I was skeptical. If this easy upgrade to the car had such a positive impact, why didn’t the manufacturer do it in the first place? Was the power gain actually real or just a desired mental outcome? Where was the proof?
To me, it seemed that moving an air intake a few inches to the side and taking it out of a sectioned off airbox would only give it access to warmer ambient air in the engine bay, which would have the opposite effect of cold air.
Apparently I wasn’t alone. Lots of debate surrounded the claims as to the effectiveness of the CAI, and despite some modders showing their before and after dyno results, I still wanted more proof. Luckily the veteran modders and pro mechanics behind the “Mighty Car Mods” YouTube channel had the same question on their minds and decided to settle things once and for all with several dyno runs of an R34 Skyline featuring different airbox setups. The video is below, which is very well done, but if you don’t want to watch the whole thing, scroll down to see the results.
In the end, each set up of a CAI resulted in less power than the simple stock airbox with the stock filter. Only when the CAI was literally placed outside of the engine was there a very small gain in power. It’s hard to argue with the dyno numbers, which offer definitive proof that the perceived power gains and my 15 extra horsepower for my Miata were too good to be true.
In short, if you want a better noise when you put your foot down and a better looking engine bay, get a CAI. But if you want phenomenal power gains with a bolt-on mod, however, it’s best to leave the CAI option out of the picture.
*Years later, my opinion is that no bolt-on mod is really that effective. There is no replacement for displacement or adding a forced induction.