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Old 09-16-2014, 04:55 AM   #1
joejoe69
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Default DIY Cobb SF Intake Airbox 2015 WRX STI

Hey everyone,

I just wanted to share my custom made Cobb SF Intake airbox for my 2015 WRX STI that's constructed with 1/8" thick Kydex (http://en.m.wikipedia.org/wiki/Kydex), which is popularly used for knife sheaths and gun holsters. Cobb has not released an airbox for the 2015 WRX STI so I figure I make one myself.

Since Cobb's airbox is made of metal, heatsoak is inevitable no matter what type is used. The stock airbox is made of some sort of ABS plastic, so I went ahead and searched for something that was durable as well as easily manipulative. That's where I found Kydex.

My design of the airbox is similar to Cobb's but with less openings to help shield heat away completely. I also added some heat insulation and barriers to help cope with the extreme temps under the hood of the STI.

Here is some Kydex that I purchased from Amazon.com. (http://www.amazon.com/gp/aw/d/B00BR38ZS8?pc_redir=1410740076&robot_redir=1)
I bought 2 sheets of 12"24", 1/8" thick. As you can see, the texture is nearly the same as the OEM intake snorkus.




Here's my mockup, made of a USPS large flat rate box. Notice how the large openings and areas where heat can easily find its way inside the box is covered.






Now that it fits, time to make it reality.
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Last edited by joejoe69; 02-10-2015 at 03:42 PM.
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Old 09-16-2014, 04:56 AM   #2
joejoe69
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I used heat gun, wood, and some vise clamps as a break to help the Kydex bend to shape.





As tedious as it was, I can't remember how many times the filter and MAF housing came off and went on. It fit perfectly though...



Taken off one more time for heat insulation, courtesy of Heat Shield Products' Lava Mat, which is heat resistant up to 1200F, 2000F spontaneous. The interior of the airbox was also insulated with DEI heat barrier for extra heat deflection.

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Old 09-16-2014, 04:57 AM   #3
joejoe69
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Prior to building the airbox, I insulated the bottom of the intake snorkus, blocking radiator heat. Believe it or not, it actually works. http://www.iwsti.com/forums/4051343-post1.html



The box is finally installed and covered. The front lower section behind the passenger headlight still needs to be made and I'm also waiting on rubber trim to finish it off.






Be back when it's completely done...
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Old 09-16-2014, 09:41 AM   #4
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that looks killer! nice work. are you going to do some before and after IAT logging?
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Old 09-16-2014, 09:44 AM   #5
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^5 for a job well done
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Old 09-16-2014, 11:26 AM   #6
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Well done, and terrific write up.

Quote:
Originally Posted by joejoe69 View Post
so I went ahead and searched for something that was durable as well as manipulative. That's where I found Kydex.
Just remember to be your own man, you don't have to do everything that manipulative kydex tells you to.

Last edited by KrazyKarl; 09-16-2014 at 12:23 PM.
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Old 09-16-2014, 03:34 PM   #7
joejoe69
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Quote:
Originally Posted by isotopesope View Post
that looks killer! nice work. are you going to do some before and after IAT logging?
Thanks, yup.

Quote:
Originally Posted by Bad Noodle View Post
^5 for a job well done
Thanks.

Quote:
Originally Posted by KrazyKarl View Post
Well done, and terrific write up.



Just remember to be your own man, you don't have to do everything that manipulative kydex tells you to.
Thanks. And thanks for the advice.
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Old 09-16-2014, 03:37 PM   #8
Restomage
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This is pretty cool! Before reading I thought you were actually going to use the USPS box, I was like "um...what?" lol
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Old 09-16-2014, 09:33 PM   #9
joejoe69
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Finshed the front bottom section behind the passenger headlight. I bent another piece up and slapped some more heat barrier and lined a couple of the edges with rubber seal to prevent cutting/shorting wires. It's secured by a pop rivet and some industrial velcro.




Here is an IAT comparison. My daily commute consists of 70% highway, 30% stop 'n go during the hottest time of day. I let the engine warm up and then reset the AP before going out to drive. Don't mind the actual values, pay attention to the temp deltas.

Check here for other stock values: http://www.iwsti.com/forums/4051344-post2.html

Before (Stock airbox, non-insulated snorkus):

Ambient: 90F
Min: 99F (+9F)
Max: 133F (+43F)
Cruise: 104F (+14F)

After (Cobb SF Intake w/Kydex Box, insulated snorkus):

Ambient: 90F
Min: 91F (+1F)
Max: 100F (+10F)
Cruise: 97F (+8F)




Overall, I'm totally impressed. This costed me about half the price of the actual SF airbox, which still allows heat to to be drawn in.

Max values could be higher if I were to stay in traffic longer. But it takes way more time to get to 100+F like it used to without the airbox or with the stock airbox.

Last edited by joejoe69; 09-16-2014 at 09:39 PM.
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Old 09-16-2014, 09:49 PM   #10
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Airbox looks awesome. Nice craftsmanship.
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Old 09-16-2014, 09:52 PM   #11
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make me one lol
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Old 09-16-2014, 11:40 PM   #12
joejoe69
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Quote:
Originally Posted by Brandon2k13 View Post
Airbox looks awesome. Nice craftsmanship.
Thanks.

Quote:
Originally Posted by whitefrs View Post
make me one lol
Lol. I got rid of my cardboard templates. I would've shipped them to you and you could've fabbed it yourself.
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Old 09-18-2014, 12:24 AM   #13
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Looks much better than the cobb box. Great work.
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Old 09-18-2014, 12:32 AM   #14
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Quote:
Originally Posted by mazdan View Post
Looks much better than the cobb box. Great work.
Thanks!!
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Old 09-18-2014, 10:47 AM   #15
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Awesome work! Did you also seal around the top? Will definitely be sending this over to our hard parts team to check out!

[email protected]
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Old 09-18-2014, 01:35 PM   #16
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Well DONE!!! Looks fantastic!

Bailey
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Old 09-18-2014, 05:36 PM   #17
joejoe69
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Quote:
Originally Posted by Cobb Tuning View Post
Awesome work! Did you also seal around the top? Will definitely be sending this over to our hard parts team to check out!

[email protected]
Hey Marshall,

Thanks. I haven't sealed the box with rubber so far because my order for them hasn't arrived yet. Looks like its coming today according to my tracking and I'll definitely try that out if it can work.

I have used 1/8" thick Kydex V for my box however I'm also thinking of making another box using 1/4" thick Kydex T which can probably withstand more heat and stress than the latter.

Another thing I noticed is that the engine undertray below exposes heat from the exhaust manifold and enters the wheel well. It's that heat that also causes IATs to increase while at a stop. Cold air intakes like AEM, Mishimoto, or Injen think they got it good by having the filter relocated down there but it's just as bad. If that section can be blocked somehow, it can effectively drop temps.

I am also adding an active cooling device with a thermal sensor and a fan when the car is at a stop and/or at a determined high temperature, when heatsoak is more prevalent. The fan will then turn off at a determined cooler temperature and/when the car gets moving.
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Old 09-18-2014, 05:36 PM   #18
joejoe69
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Quote:
Originally Posted by Bailey View Post
Well DONE!!! Looks fantastic!

Bailey
Thanks!!
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Old 09-18-2014, 08:04 PM   #19
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that dei heat barrier, you have a part # for it? the only thing i see on their site is $115 for a huge roll..excellent work though!
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Old 09-18-2014, 10:17 PM   #20
joejoe69
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Quote:
Originally Posted by BigRob74 View Post
that dei heat barrier, you have a part # for it? the only thing i see on their site is $115 for a huge roll..excellent work though!
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Old 09-19-2014, 05:07 PM   #21
joejoe69
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So here's the rubber seal I used that I bought it from Amazon. It's for 1/8" panels and has wires running through it to retain its shape. It fits so snug in and around the box that there is no way heat can make its way in from outside. The MAF housing and intake snorkus needs some good pushing in to get them mounted in the box. The lid also got some rubber to provide an extra seal from the top.





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Old 10-18-2014, 02:41 AM   #22
hangmanfsc
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I must say, your finished product looks like it came from a professional rather than a DIY. In theory, this should work great keeping out the hot air in the engine bay, and only allowing fresh cooler air in the box. BUT what about after it leaves the turbo?

I am doing some reasearch on a CAI for my '13 sti and the same delima I asked the local parts shop. He informed me with a shield or not; the air is going to get hot by heat soak through the hot side of the turbo (and the temp of the "cold" side of the turbo is always be well over 100F)

Hence it seems like no matter what your IAT's are, the main area to focus on is after the charged air leaves the turbo (intercooler).

Not ragging on your design/creation, just trying to get a better idea on the topic.

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Old 10-18-2014, 07:39 AM   #23
joejoe69
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You're local parts guy is right and wrong.

Yes everything will get hot post turbo, intercooler, as well as the intake manifold, and everything else the engine is connected to. But he's not realizing what the IAT sensor is for and why cooler air through the intake helps with power production.

The IAT sensor works in unison with the MAF sensor. While the MAF measures air density, the IAT sensor measures, well...air temperature to determine how much fuel can be delivered for optimum performance and fuel economy, at the same time, also determining how much timing advance can be applied at a given load prior to air/fuel entering each cylinder. High IATs or hot ambient air lowers performance by pulling timing to avoid knock or detonation. Without the importance of the IAT sensor, the turbo will just be forcing hot air into the cylinders, with the ECU and MAF not compensating enough for any changes to offset timing and fuel. The intercooler is the mechanical or static way of cooling the charge after it is compressed by the turbo, but is not enough to prevent knock or detonation on its own.

So TL/DR, the cooler the air passing through the IAT sensor, the more timing advance can be used, relative to fuel delivery for max power and efficiency before the charged mixture reaches all cylinders.

For example, on my dyno runs with this airbox and stage 1 tune, temps started off hot (91F ambients and 133F while off and sitting). But as the fans cooled the engine off between pulls, power gradually increased run after run, even after my tuner made final adjustments.



Here's my final result. The top pull is S#, the middle pull is S mode.



My mods are:
Cobb SF Intake w/kydex box
Cobb AP V3 Stage 1
Perrin AOS
Nameless Catback

Last edited by joejoe69; 10-18-2014 at 08:02 AM.
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Old 10-18-2014, 09:32 PM   #24
hangmanfsc
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Thanks for the info! This is very informative. What type of dyno were you tuned on?

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Old 10-18-2014, 09:47 PM   #25
joejoe69
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It was on a Dynojet at sea level.

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