I didn’t plan on doing this mod anytime soon, as I didn’t really want to spend $3XX on a “hot air intake” as some people like to call them; but one popped up locally for cheap so I grabbed it. I had originally planned to do an install write-up of this intake, but the install is pretty straightforward. Plus my part was used and preassembled. So instead of an install write-up, I thought I would just do a review for those considering an intake.
I also planned to do a bunch of logs and create some charts and make this super scientific-like. I was pretty stoked about it.
Now, I have run this intake before on my old 2005 STi, and I definitely noticed a drop in power after I removed it. I think the internet finally got to me about running a “hot air intake” on my Subaru, and I was tired of the noise it made, so I removed it.
So my expectations were pretty low for the champion of the mid-range powerband – the EJ207.
However, once installed, I noticed that I had improved turbo response. On the stock intake, the stock turbo felt pretty lazy under 4000RPM. I could reach full boost (15PSI ) at around 3600-3800RPM; with 3800RPM being more common. I dropped the boost down to preserve my clutch life. On the K/N, I was hitting 15PSI at around 3400-3600RPM; with 3400RPM being more common, and on occasion reaching 3200RPM.
This is under WOT conditions.
Since I don’t drive under WOT conditions everywhere I go (and hopefully you don’t either), and frankly, it is the least of my concerns on a daily driver, I decided to take note of partial throttle response. This doesn’t involve any datalog comparisons as I don’t even know how to make consistent part-throttle acceleration events to make an accurate comparison. Nor did I have the time to do so.
Tip-in throttle response is much better with the K/N intake; so much so that I can drive up a gear from the previous setup (third gear situations can now be handled by fourth gear). I rarely have to do the cringeworthy, very low-speed, but still moving first gear double clutch downshift anymore.
Rolling into boost is so much easier, requiring less throttle input and overall, less RPM per gear, that my exhaust became super quiet. So much so that I bought another axle back to wake it back up (install/review coming soon).
In the Subaru community, there is still an on-going debate over whether cold air or short ram intakes are “worth it”. Nevermind that worth in this context is pretty subjective. If your goal is to get to 200,000 miles with minimal issues, then your “worth” would be different from someone looking squeeze all the performance they can out of the stock turbo. Or as in my case, you are looking for better turbo response with reasonable trade-offs (e.i. higher IATs but with no knock) then it might be worth it to you.
Make no mistake, short ram intakes will increase your IATs. Some are worse than others. In my case, it was 10-20°F (in 90°F weather) higher than the stock intake. If this is a deal breaker for you then stick with the stock intake or try a true cold air intake.
I have some plans to try and bring those IATs down some more. I want to insulate the box and the portion of the hood where the box seals against (or build a cover for the box). I would love to make a carbon fiber version of the box as well. I also want to relocate a few warm items to the firewall like the coolant expansion tank. That tank actually gets pretty hot as I’ve burned my arm on it a couple times.
Getting back to the response of the intake, one of the best methods I’ve found for testing parts by feel is to drive around with them installed for a week or so, then switch back to the stock part. If you don’t notice anything different, leave the stock part on the car and sell the aftermarket part and move on.
After putting the stock intake back on (along with the appropriate tune) I regretted that decision almost immediately. First, the exhaust sounded different; it had a lot more drone to it. I have no idea why. Second, and more importantly, the throttle response was lazier than I recalled it being. On paper, 200-400RPM doesn’t seem like a lot, in fact, it almost seems downright negligible. However, when you lose that much spool when you previously relied on it, the increased turbo lag can feel like an eternity.
One potential reason for this change in turbo response is the long path of the stock intake. At nearly four feet in length, the stock path is quite a journey to get to the compressor, almost like drinking through a long krazy straw. The K/N intake effectively cuts this path in half, making the initial point of entry in the stock system a secondary source. Obviously, the K/N draws from a hotter primary source of air than the stock setup, but the tradeoff is slightly faster spool-up. This probably less of an issue on EJ255/EJ257s with their +0.5L of displacement or on UEL equipped EJ205/EJ207s.
After returning home from class, I put the K/N intake back on. Life was good once again.
Except for that MAF wire routing; I absolutely hate that MAF wire routing.