DIY 3.5” Air Intake

Hey guys so im new here but am thinking about putting a bnr s4 on my speed 6 this spring... I am a little cautious about relocating my ecu stuff and thought about making a custom 3.5” intake.. It would save me money (I work in a weld shop)
and could save me time if I was to clear the ecu without moving it right? Anyone ever tried this?

******** UPDATE WITH HOW TO *********

Ok so I created this thread in hopes of making my own air intake to save money and know it was made by me and not someone else. I want to give others the reassurance that it isn't very difficult and will cut your 3.5" - 4" air intake cost in half!

To start you will want some solid aluminum piping material. I went with some 6061 which welds nicely and is of high quality. I purchased a 2ft long 90 degree piece that was 3.5" diameter and a weld on MAF flange made for 3.5" pipe.







MRP performance seems to make very very nice quality weld on MAF flanges and that is who I chose for that. Then I cut the pipe at an angle best suited to aim the intake from the turbo outward from the block. I had no special tools for this but just simply tried to go for what I felt like was a cut to make one half have a 60* bend and the other half have a 30* bend. I used a little band saw I have and it ripped right through it but barely fit lol
(After having it mocked up it would be better to cut it at a sharper angle or make sure your 60 is 60 degrees as mine seemed shy and isn't quite as angled as I would like)



A belt sander would be my preferred method to make the cut nice and flat afterwards but I had to use a flap disc on a 4.5" grinder and use the ol' eyeball method haha After that I checked with a mazda homie on how far his MAF sensor was from the end of his intake and he said about 4" and has had no issue and doesn't have an air straightener, so I went with that or more. I pre-drilled a pilot hole for my hole saw and cut a hole that was the same inside diameter as the maf flange hole. The hole size should be one and a quarter inches so 1.25".
https://performancemrp.com/images/F198642096





I cleaned up the burs that were around the inside with a inverted dremel bit on my drill since my pneumatic dremel is annoyingly loud. Once I had the pipe cut and the maf placement found and cut I mocked it up on the car how I wanted it all positioned. I will say I actually checked the MAF placement before cutting the hole for it on the car because I wanted my maf to be unseen and on the bottom of the air intake. After finding the correct orientation for it all I taped it all together and marked it with a sharpie across the joint onto each piece of pipe in case it came untaped.



I had to take off the stock bulky plastic piece on my wiring harness as it was kind of in the way for how I wanted the intake to be placed.



I rewrapped the wires in very good quality electrical tape nice and tight and with a double layer. I will also add here that I have an EGR delete and relocated my battery about a year ago to make sure that this would fit nicely without any hassle.

I found a friend in my union local to weld it up luckily but had a couple estimates to have it welded (before it was made to where they could look at it and really get an idea) and they said anywhere from $100-$150 (based on $100/hr shop time). All in all it turned out great and has had zero issues since the install and did not need an air straightener.


Good luck guys and hope this helps someone!!!

 

Do you have the ability to make the MAF flange? if so then it shouldnt be too bad. but that will be the only thing that might hang you up.

 

Oh ok well i have seen where they do sell them right? I was thinking of just welding all the piping and putting a purchase MAF housing in the intake close to the factory placement... They do sell them right?

 

Yes I think a couple people make them but I know they're not particularly cheap from what I remember.

You may want to try fitting the tubes 1st because I don't know if you'll be able to not relocate the ECU. There isn't a lot of space in a speed 6

Sent from my SM-G950U using Tapatalk

 

MS6 MAF flange?
https://www.treadstoneperformance.c...r+Flange,+Subaru,+Scion,+Mazda,+Toyota,+Lexus

 

Thanks for the link and yeah that’s exactly what I would need.. Ill just have to see so much cheaper it would be and see if it would be worth it... I mean if I could build it for even $150 instead of a $300 JBR then I probably would go that route lol Thanks guys for all the help!!!!

 

You can also watch for a used one, they seem to usually go for $200-250 in the facebook sale groups.

 

Alright sounds good man thanks!
I am currently deciding between a street bike or my bnr s4 build on my ms6 but I have pretty high mileage so idk...

 

The ms6 ecu isn't in the engine bay. You won't have to relocate anything

 

The main issue with big intakes on the MS6 is the battery. I barely got a JBR 3 inch to fit with the stock size battery and tray. A 3.5 inch with an S4 will require a smaller battery and tray or a battery relocate.

 

Well I keep reading something about the ecu wiring harness or something to do with the wiring under the intake that has to be relocated... So how hard is a battery relocation to the trunk or where else is best? i dont really want to have to buy special smaller batteries and what not for it really
[doublepost=1520043021][/doublepost]

So I could fit a 3” intake without a battery relocation then though right!?

 

You can do a 3" with the stock size battery but you will have to cut the tray to make it fit, and the JBR at least just barely fits. That's what I did, but with an S3, which may not stick out as far as an S4. I think most people switch to a smaller 51r battery and tray, and then you can run a 3.5" no problem. Battery location isn't really required for either, just a smaller battery for the 3.5".

You could probably just cut the stock tray and figure out a solution for the battery strap, and then go get a 51r battery, and be able to fit the 3.5" no problem.

 

I would just go with the 3.5 seems like the intake can never be big enough on these cars

 

Oh alright guys sweet sounds like I'll be getting a 3.5” then most likely lol I just bought a new battery though so it sucks having to buy another one that’s just smaller...haha Oh well I guess it’s just more money right??hahaha
[doublepost=1520205056][/doublepost]Why did I keep hearing people say something about relocating the wiring to fit a bigger intake? Any of you guys know what msf guys were referring to?

 

There is a harness that runs near the turbo inlet pipe you might have to shift around depending on how you angle your piping, but it not a big issue.

 

Oh ok so its possible to run a 3.5” without moving it possibly? I am thinking about having someone TIG a custom one together here at work.. You think I would need an air straightener or do they not do that much really?

 

Unless you can get the maf in a straight section of piping you will need an air straightener..

 

So the stock location toward the front of the intake should be alright? Ill post a pic here in a bit..
[doublepost=1520348768][/doublepost]This is where mine is now is that where I should put it on the 3.5” intake too?

 

You need to try and get at least 3-4" of pipe before the maf.

 

You could do a blow thru setup since you wana fab stuff then just stick a mushroom filter right on the turbo itself!!!! No need to touch the ecu or battery. Then you can VTA the BOV. Once and a while i go half vta just to cheer my self up when im feeling blue.

You should get a air stratiner. I can't say its required since i ran a 4" intake without one but i had wonky idle readings until i put one in. There is a formula on msf for proper spacing from the maf. The thread is a great read i would check it out. I won't link it but its titled "MAF Airflow Straightener Testing" Here is where i got my maf honeycomb. http://www.saxonpc.com