Installing a Mishimoto Performance Cold Air Intake
The Mishimoto Performance Cold Air Intake is officially the first performance install for my little-ole 2015 Subaru Impreza WRX STI. And, thus far, I’m quite happy with it. Like I said in my first build post, while I’ve done pretty much every repair you can imagine on a car, this is my first real performance wrenching. So, I decided to start with an easy upgrade that may actually deliver pretty decent gains in terms of power and aesthetics.
Before finally picking the Mishimoto Performance Cold Air Intake, I did quite a bit of homework, researching intakes from AEM Performance, Perrin Performance, Cobb Tuning and a host of others. While the expected benefits for each CAI were pretty much on par with the others, the Mishimoto system offered one serious plus… No tune.
Subaru’s manifold absolute pressure sensors (aka MAP sensors) are notoriously finicky. And, as the map sensor is mounted on a car’s intake, measuring airflow to optimize the fuel-air mixture, playing with it can result fuel-air issues. That’s why, instead of designing a cold air intake that works with factory fuel-air maps, most intake makers require a tune to the car’s ECU for the intake to work properly.
Not so with the Mishimoto Performance Cold Air Intake and the 2015 Subaru WRX STI. The Mishi CAI is plug-and-play, a direct fit for the 2015 STI requiring no tune to get a (Mishimoto claimed) max gain of at least 20 horsepower and 18 pound-feet of torque, both at the wheels. That’s pretty good power gains.
That’s the theory of it. So, what about the reality?
I pre-ordered the Mishi CAI a few months back for $265 and got it just last week. The price now, by the way, is $325. I was quite eager to install it, but hit a bit of a roadblock. No instructions. Mishimoto shipped the first orders of their 2015+ STI cold air intake before the written and video instructions were ready.
But, I wasn’t about to let a little thing like lack of instructions stop me. Thankfully, there are a number of videos on YouTube explaining how to remove the stock intake (the watching of which turned out to be not really necessary since the whole thing is held in with three screws, two clips and a worm-gear clamp).
The second half, being the actual installation of the new intake, was really, really simple. Once looking at a photo of how the thing is supposed to fit together, assembling it was a piece of cake. And, once the intake pipe, mounting bracket, rubber flex-point, heat shield and air-filter were assembled, it only fit into the car one way.
Since there was no tune to worry about, after everything was snugged down tight and the MAP sensor was back in place, I was off to road test my first performance modification after an install time of 37-minutes. Not bad. And, I only needed a 10 mm socket wrench with six-inch extension, a Phillips-head screwdriver and a flat-head screwdriver.
The first thing I noticed, before even pulling out of the driveway was the sound… or should I say sounds. With the much freer air flow resulting from the Mishimoto Performance Cold Air Intake, you can really hear the air being drawn in through the filter. The 36-ounce coffee-can sized Mishi filter has about 16-percent more surface area over the stock filter, and the resulting noise is pretty loud and not displeasing.
The second noise, which as also noticeable almost immediately, was actually the lack of noise in the cabin. Subaru jumped on the piping-engine-noise-into-the-cabin bandwagon with the 2015 STI. Unlike the Porsche and BMW systems that use the radio to “enhance” engine noise, Subaru used a sound symposer, which is basically a plastic sound-transfer tube leading from the stock intake into the cabin. New intake equals no plastic tube. In fact, Mishimoto includes a little rubber stopper to cover the old sound symposer connection. As a result, the interior of the car is much quieter and a much more pleasant place to be. (especially at high revs).
The best new noises come from the turbo and blow-off valve. The stock intake has a milk-gallon-like resonator at the bottom, which quiets most of the turbo and turbo-associated noises. The Mishimoto CAI allows the turbo to sing. The more you push the car, the more you hear a glorious turbo whine. Let off the throttle, and the pppptuuuush of the blow-off value is heard loud and clear. Admit it, everyone actually loves that sound, as d-baggy as it might be.
The myriad of pleasing melodies coming from my 2015 STI and its new cold air intake are nothing, and I mean NOTHING, compared to the immediate boost in power. While 20 whp or so may not seem like much, it is. The stock 2015 WRX STI bhp is 305 hp, meaning the stock wheel-horsepower is 247 hp or so. So 20+ more ponies is nearly a ten-percent gain. That gain is immediately apparent when you push the car. It accelerates faster, has a snappier throttle and happier-spooling turbo in all driving modes (Intelligent, Sport and Sport-Sharp). Pretty good for 37-minutes and $325 (or $265 if you bought early).
So far, I’ve driven about 250 miles with my new Mishimoto Performance Cold Air Intake on my 2015 Subaru WRX STI, and I’ve had no issues. I’m still averaging about 20 mpg in my daily commute. I have no evil lights popping up on my dash. And, I’m ready for my next performance install. I just need to figure out what it should be… Off to research Cobb, Perrin and Mishimoto’s sites some more.