[UPDATE] Per a recent video that I’ve found, apparently this mod will give up to 10 horsepower on these cars. I’ve embedded the video below and you can view his dyno results for yourself. Even better, and still $Free.99.
Do you love free shit? I love free shit. And I’ve got some free shit for you. Specifically, up to 10 free horsepower (dynoed, see video below), plus a side helping of torque. “How can this be?!” you ask. Simple, you remove the charcoal filter that’s in your airbox, which eliminates some airflow restriction, and you get free power and torque. Even better, it only takes about 15 minutes to do; maybe less if you work fast.
Of course, you’re probably wondering if there’s any downside to this modification. As far as I can tell, nope, not a one. In fact, from what I understand, JDM BRZ/86 airboxes don’t have a charcoal filter at all; it’s a USDM thing (and maybe some other countries as well) that’s included for eco reasons to filter out fuel vapor that may get back to the airbox from the intake side of the engine. With that said, I should probably give the typical disclaimer that since you’re tampering with emissions equipment technically you’re making the car illegal to drive on public roads (depends on your state), so it’s up to you to decide if it’s something you want to pursue. For the purpose of this post, however, I’m going to assume you’re primarily tracking your car and thus want to extract every ounce of performance out of it that you can. Right? Right. Also, understand that you, and only you, are responsible for any damage that might occur while performing this mod, as well as any damage that may occur later as a result of performing this mod on your car. It’s pretty harmless, but still, you assume all risk if you decide to proceed. Now that that’s out of the way, let’s begin.
The first thing you need to do is to unclip the the lead that connects the MAF (Mass Air Flow) sensor to the car’s electrical system. You’ll find that at number 1 in the photo above, and all you do is press the tab on the plug down enough to free it while you gently pull it away from the sensor (DON’T PULL BY THE WIRES!!). Once you do that you’ll notice that the lead is attached to the intake box via a small clip. To free the lead you simply have to press in the two tabs that keep it secured in the hole and it should come out without any fuss. I find a small pair of needle-nose pliers helps, but you can use your fingers as well. Whatever you do though, DON’T try to force it out of the hole as you run the risk of damaging the lead and well, that’d be very bad because then your car won’t work anymore and will cost money to fix. Be gentle.
Next thing to do is to loosen up the clamp that tightens the intake hose onto the air box and keeps it in place. You’ll find this at number 2 on the photo above and all you need is a Phillips head screwdriver. As with anything, make sure you use a properly sized screwdriver so as not to strip out the hole on the head of the bolt. You also don’t need to remove the bolt, only loosen it enough to allow the box to slip out easily when you remove it.
Lastly, you need to pop open the two silver clips holding the airbox together. Once that’s done, you’ll be able to wiggle it open enough to pull it back and kind of twist it a bit in order to free it from the hose you just loosened. Be careful not to damage the air filter still mounted in the remaining half of the airbox, as well as any of the surrounding pipes, hoses, and so on. By the way, this is also how you change the air filter on your car, so if you were to go no further, replace the filter with a new one, and put everything back the way it was, you just learned how to save yourself some money from not having to have the dealer or a repair shop do it for you.
Anyway, once you have the airbox half removed, it should look like the photo below.
Now we’re getting to the meat of the modification. That white mesh thing is the charcoal filter that you want to remove. As you’ll notice, it’s sort of spot-welded into place and doesn’t just fall out. Basically, to remove it you just need to get something under one of the edges and lift it enough to be able to get a decent grip on it. At that point then, you only need to rip the filter out by pulling on it enough to free it from the welds. It’s not hard to do and it comes out pretty easily. You also don’t have to worry about it getting damaged since it’s going to get tossed away anyways. Once it’s out, you’re going to notice that there’s likely some loose fibers remaining that are attached to the welds still, so I suggest getting a pair of scissors and a small knife out to trim those off. You want to get them all because naturally you don’t want them getting sucked into the engine while it’s running, so take your time and be thorough. When you’re finished, you should have no loose fibers anymore on the airbox and it should look like the photo below. It’s OK if there’s still some filter material solidly attached to the welds, but what you don’t want is loose strings and fibers hanging around.
At this point, you are technically done with the mod, so congratulations! The filter has been removed from the airbox and now all you have to do is to put everything back together in the reverse order and you’re good to go. Before re-assembling everything, I would also suggest to wipe out any dust or debris that the airbox half might have in it with a clean lint-free towel so as not to have it get ingested into the engine when you next use the car again. Also be careful not to touch or damage the MAF sensor either, or again, you could end up with a car that doesn’t work and money out of pocket to have it repaired.
And that’s that. When everything is back together it should look like the photo below, with the hose clamp tightened enough to seal it and hold it into place securely, the MAF sensor plug attached and the lead snapped back into place securely, and the airbox halves should match up together tightly and cleanly.
[EDIT] As mentioned earlier, I’ve found a video that shows a 10 horsepower gain on these cars, and it’s a dynoed result, so that is the potential increase that I am advising you can get. That said, I will leave my following comments in their original form as my driving observations haven’t changed and I still think there is value in the discussion about the ROI of performing the mod.
Now the big question – what are the results of this mod and is it worth it? What you get for doing all this is a small increase in overall HP and torque. How much is up for grabs, and without running a before/after dyno test you can’t know for certain. That said, if you watch the video I’ve included below about this mod that does just that and also performs some real-world performance tests, it’s probably safe to assume you’ll see similar results with the BRZ/86, which amount to about 4 HP and 4 ft/lbs of torque more than stock. Since this is a different engine altogether, it may vary somewhat in either direction from the results in the video, but I would think it’s pretty similar. And as for if it’s worth it or not, the video addresses that as well and in real-world testing there is a measurable increase, so in that sense it’s not ineffective. Whether it amounts to anything noticeable using your butt-dyno is another thing. For me, the car feels pretty much the same as it did before the mod, and I don’t notice any real change in performance or sound after having done this and driven around town at normal city speeds. I may feel something when I push it harder at higher speeds like on a track, but for normal everyday driving it’s a wash I’d say. Still, if you compare this against some of the fancy and costly intake kits that are on the market that net similar gains, and this is free, well, that’s of value right there I’d say. Plus, add a performance filter to the mix and you will gain even a slight bit more from all indications, so there’s that too. Ultimately, it’s your choice if you want to give it a shot. Just remember it’s not reversible unless you buy a new airbox half, though I wouldn’t worry as again, it seems JDM cars don’t have these filters and they’re getting along fine without them every day.