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Stock Air Box mod questions

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#1
So can any of you guys who have done the mod where you drill holes in the box tell me how loud it actually makes it? I know its supposed to enhance the "psssssh" turbo noise. But can you actually hear it in the car with windows up is what i really want to know. Any info or tips on the best way to do it would be appreciated!
 


MKVIIST

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#2
It does but not by much. You can hear it better on the highway at higher RPMS.
 


Hijinx

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#4
^^^ Same here. A FoST owner asked me if I have a VTA, if that's of any help. I was skeptical at first, but in combination with Mountunes drop-in and silicone pipe, it's a cheap CAI that's worth the money/time...as long as you're not fording rivers (pun totally unintended, but dealwithitdog.gif). I put some screen door mesh in the bottom of mine to help ward away bugs, litter, etc.
 


iso100

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^^^ Same here. A FoST owner asked me if I have a VTA, if that's of any help. I was skeptical at first, but in combination with Mountunes drop-in and silicone pipe, it's a cheap CAI that's worth the money/time...as long as you're not fording rivers (pun totally unintended, but dealwithitdog.gif). I put some screen door mesh in the bottom of mine to help ward away bugs, litter, etc.
I'm thinking of doing the same as you. Get a silicone pipe and then cut off the bottom of the stock airbox with a large bandsaw.

I need to go look up your build thread to see what you did with your box porting.
 


Hijinx

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#6
I'm thinking of doing the same as you. Get a silicone pipe and then cut off the bottom of the stock airbox with a large bandsaw.

I need to go look up your build thread to see what you did with your box porting.
Unfortunately, I didn't start a build thread... For my box, imagine if the air box is upside down. Instead of chopping it off horizontally, I followed the pattern and cut out the bottom vertically. A band saw would have been easier though. For the screen door mesh, I folded it over the bottom of the box and inserted it inside. I plan to go back in with some plastic weld to make sure it stays in place. I also might look into some kind of fabric that I can soak in water repellent.
 


iso100

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#7
Got it. Thanks for the update. Do you have any logs before and after related to intake temps?

I'm also wondering if you have more intake noise.
 


BlueBomber

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for those interested in datalogs etc see the "UNLIMITED PLENUM INTAKE" thread.

Personally, i used a 2" round holesaw on the bottom and then mated a 2" ducting coupler and plumbed the ducting into the fender. This looks close to OEM. I then ported out a small 2x3" or so area on the side of the lower airbox that faces the backside of the headlight for more noise than OEM and better flow but without looking hacked up or janky.

Should work GREAT with Cobb unit.
If you're considering the Cobb airbox later hacking off the entire bottom is not a good idea as you'll ruin the entire advantage of the "sealed airbox" type design and drawing from where you are straight down in the engine bay it will be drawing hotter air temps, hence why I ducted.

Just a suggestion and I advise a little bit of caution before you cut the entire bottom half off.
 


Hijinx

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Got it. Thanks for the update. Do you have any logs before and after related to intake temps?

I'm also wondering if you have more intake noise.
As Blue said, I'm guessing you could check that thread. I have datalogs out the wazoo, but none right after I did the mod. I will say this though; it actually does make a difference. And I agree with Blue, chopping half of it off is not a great idea; just the tip is all you need. However, in retrospect, a nice hole in the side with a duct is a pretty good idea.

And yes, there's plenty of intake noise. Love the turbo sound.
 


BlueBomber

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As Blue said, I'm guessing you could check that thread. I have datalogs out the wazoo, but none right after I did the mod. I will say this though; it actually does make a difference. And I agree with Blue, chopping half of it off is not a great idea; just the tip is all you need. However, in retrospect, a nice hole in the side with a duct is a pretty good idea.

And yes, there's plenty of intake noise. Love the turbo sound.
Right. Opening up the bottom a LITTLE is OK but like cutting the entire lower half off is not smart.

You'll get more noise if you open up the side of it - also see SEKRED's "SEKTUNE" intake for some ideas to get more whooshy-whoosh using the OE airbox and a couple cleverly inserted bits of PVC.
 


iso100

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And yes, there's plenty of intake noise. Love the turbo sound.
Right. Opening up the bottom a LITTLE is OK but like cutting the entire lower half off is not smart.
Thanks guys. I wasn't talking about literally cutting it in half but rather opening the bottom. Guess I should refer to some images of the thing since I haven't even removed it from the car yet.

I have a friend with a 3D printer so it might be nice to make a proper ducting hose connector with velocity stack inside, etc.

I'll go check out the suggested threads for details.
 


BlueBomber

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Thanks guys. I wasn't talking about literally cutting it in half but rather opening the bottom. Guess I should refer to some images of the thing since I haven't even removed it from the car yet.

I have a friend with a 3D printer so it might be nice to make a proper ducting hose connector with velocity stack inside, etc.

I'll go check out the suggested threads for details.
SEK has done a great job with creating a kind of velocity stack thing. I am only adamant cos a local FiST owner cut the entire bottom half off his... then needed a replacement unit STAT to get another type of intake... Be cautious and don't overdo it is all the advice I have, and be sure to keep your cuts clean for a better look. :)
 


iso100

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I am only adamant cos a local FiST owner cut the entire bottom half off his... then needed a replacement unit STAT to get another type of intake... Be cautious and don't overdo it is all the advice I have, and be sure to keep your cuts clean for a better look. :)
Hmm... what was the issue that caused the panic? Was he trying to get a new intake that required a functional bottom box?

I guess it's time I go look at my car and see what the box and stock air snorkel looks like. Seems that no matter what, adding the BPV noise will require cutting holes that open into the engine compartment instead of into sealed ducting which means hot air when not moving... there's no getting around that...
 


Hijinx

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#17
If I'm correct in my thinking the ECU is expecting a certain fixed tolerance of an amount of air. It's not metered as a MAF equipped vehicle would be. So if that volume of air is exceeded on an untuned vehicle I imagine it would go into limp mode.

However, that's all speculation and I could be wrong.
 


re-rx7

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I cut the very bottom 1/2' off and a slit in the driver side. No problems,.
 


iso100

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I cut the very bottom 1/2' off and a slit in the driver side. No problems,.
Is that ? foot or ? inch? Did you happen to take any photos?

How about performance (any?) and/or intake BPV noise?

I'm considering doing the airbox mod combined with a Mountune hose...
 


BlueBomber

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I'm guessing he couldn't get on the gas without going in to limp mode.
Nope.

Car ran fine and all he just freaked out, as he needed it to shoot a video... and the airbox needed to be stock to demonstrate removal of OEM and install of aftermarket intake for a certain TV show
and tracking down an unmodified lower airbox proved to be quite the challenge.

Cutting the box does not appear to cause any sort of running issues.

I cut out the side facing the back of the headlight, at least that way no openings face directly into the engine bay.

charge air temps remain within 5-10 of ambient unless I'm parked running my AC on a 100* day, then i'll get 120 charge temps til I move again
 


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