A Problem with CAI/SRIs and an Alternative (yes, finally)

[williaty]

It has been brought to my attention that someone has begun selling an intake that looks identical to my hybrid intake design. The design was NOT licensed from me. I was not contacted about obtaining the rights to commercial production of the hybrid intake design. They are not acknowledging that I released the design 6-7 years before their product appeared on the market. Make of that what you will, but when you're considering making your own vs buying the one from the guys that didn't ask nicely, well, consider how much having people contribute to the community for free means to you.

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[Zac_Adam]

I did a intake install similar to ones on here with the metal pipe and the silicon connectors. After a short drive, I noticed the metal intake pipe was really hot. I know that the whole engine bay gets very hot but I decided to wrap the metal pipe in heat resistant tape. I might wrap my headers as well to try and keep it cooler in there.

[WCrispy]

Hey all. First time post here. I'm new to Subaru and this is a pretty interesting thread. My old Nissan pickup was sitting at 255,xxx miles and I really needed something that didn't instill the fear of being broken down on the side of the freeway for the commute to work. I bought myself a used 2006 2.5i Impreza from a Chevy dealership. It's really clean and the previous owner took amazing care of it.

I've had the car for a few days and I've been perusing the internet to learn all about the unique characteristics of the boxer engine because the last fun car I had was a manual Honda Fit Sport. Last weekend I watched some great YouTube videos of a Subaru master mechanic named Mike rebuilding a shortblock and explaining all the cool quirks these engines have. From the central split seam down the middle, installing the pistons last, and the awful stock head gasket issues, it's been a fun learning experience.

I used to drive an old crappy E30 and then eventually an old crappy E36, and both of these had the vane style MAFs with the flaps inside. These were notorious for going bad and sending the wrong voltage to the ECU and eventually putting the car into "limp" mode, so you could get to a mechanic. It was always a crapshoot because even the new MAF boxes were plagued with the same problem, so to save money you had to go down to the junkyard and pull a used MAF off a wreck and cross your fingers hoping it would last you a few months. I'm not sure what modern BMWs use these days because after that circus I told myself I'd never own a European "luxury" car again. Paying four times the cost for the same brittle plastic bits that fail the same as on any other car isn't very luxurious to me, heh.

Anyway, reading up on the hot wire MAF wiki vs the older vanes was pretty interesting. I keep seeing your forums here pop up in random searches I make on my "new" car and it seems like everyone is in unanimous agreement in that you pretty much do NOT touch the stock air intake due to resonance disrupting the ability of the MAF wire to function which ruins the ECUs ability to manage the fuel.

I'm not an electrical engineer so I may be completely out of left field here, but has anyone ever tried to build their own vane style MAF to combat this issue? It seems like a flappy vane wouldn't be prone to the disruption caused by resonance. Taking out the large black box sitting right at the back of the intake manifold seems like it would be a good spot to try to install a vane style MAF and then all the piping out to the filter (be it SRI or CAI in the fender) would be non problematic.

The Arduino scene allows the homebrew programmer to do a lot of powerful things. All you'd have to do (theoretically) is:

1. Get a flappy vane style MAF.
2. Examine the voltage ranges of the vane MAF.
3. Insert an Arduino into the circuit on the voltage output side of the vane MAF that translates the vane's output voltage into new voltage that won't confuse the engine's ECU (if needed).

ie. [voltage coming from ECU] ---> [vane MAF] ---> [Arduino] ---> [back to ECU]

Again, just spitballing here and even if it's a crappy idea I'd love to hear why because I like learning. The end game with this would be an easily sellable kit that allows drivers to do whatever they want on the intake side while allowing more tuning options. Vane style MAFs usually have a screw that controls an air bypass valve which allows you to run more rich or more lean depending on your application without needing to retune the electronics, just turning the screw.

What do you think? Any feedback would be greatly appreciated!

Cheers.

[rallyfan98]

First off. Mad props to williaty for all of his hard work and XanRules for his intake design. Thank you.

My 98 obs ej22e 5-speed is maf based. So, I'm going to build a hybrid intake to be on the safe side. I will post more as I build it.

[rallyfan98]

[williaty]

Originally Posted by rallyfan98

That's a HORRIBLE idea. The corrugations will absolutely destroy airflow. That will perform far, far worse than stock.

[rallyfan98]

I did so it would flex with the motor, but, I guess I didn't think about the air flow. I will take it back and get one on eBay.
Thanks

[rallyfan98]

Just bought this one. Came out to be way cheaper too.

[williaty]

Originally Posted by rallyfan98

I did so it would flex with the motor, but, I guess I didn't think about the air flow. I will take it back and get one on eBay.
Thanks

Use a high quality silicone hump connector on both ends and you'll have a LOT of flex to allow for engine movement even if you use a rigid metal pipe.

[rallyfan98]

Will do. Thanks.

[rallyfan98]

My intake tube came in to today. I will take some pictures on Friday.

[fallrisk]

Got the same setup as Roke without cutting the pipe, only thing I've noticed is sometimes (1/20 times if that) my ECU has trouble keeping up with quick rev drops, even after an ECU relearn.. Anyone else have this issue? Maybe it's my little rigged up tape job, waiting on one last silicone coupler.. ;__:

[williaty]

What are your AF Learning #1 A through D values?

[rallyfan98]

[ssssssantimonio]

Originally Posted by rallyfan98

so how did your intake go?

i used that pipe and a 45 degree bend + a straight coupler.

works like magic.

[hunterdms]

Originally Posted by formula91

Ah you finally compile it. =)



I can't wait to do this.



Might as well post what you need and how to do this, although almost everyone with some mechanical knowledge can hack one together, I can always assume there are people that don't know. I was one of them.



Parts:

Ebay Intake for 2.5RS 99-01.





Looks something like this. Anything with this design will do just fine.

I believe these usually come with a 3" to 2.75" reducer, so that the pipe will fit onto the Throttle body... unless the GC body Subarus have different sized throttle bodies...



3"->2.75" Reducer (may be included with package)



3" Coupler x 2



Metal Hacksaw (nom nom nom)



Vacuum tubes if the pipe doesn't come with it.



And some hose clamps.



---



Before we put the parts together we need to prepare the SRI metal piping to be able to fit (in this case) an 05 RS.



We need to hack off the end of the intake a little bit. (The long straight before it bends 45 degrees again at the end needs to be cut off)



And the center weld after the 90 degree turn and before the 45 that's before the long straight section should be hacked in half as well.



That's it for preparing the intake.



Here's the order in which we put it together.



From the throttle body, we put on the 3" to 2.75" reducer.

-> 90 degree section of the intake.

-> 3" coupler

-> 45 degree bend to straight section

-> 3" coupler

-> MAF Housing to Airbox



Remember to measure everything out before cutting it, but the lengths of the silicone tubing should cover any small inaccuracies.

Get flexible couplers if possible as well.



Tighten everything down and you're done.



Reset the ECU. =)



And go rescale your MAF up at the top range.

Will this work for an 03 2.5 na?

[williaty]

Originally Posted by hunterdms

Will this work for an 03 2.5 na?

03 is MAP based and none of this is necessary.

[ssssssantimonio]

Originally Posted by williaty

03 is MAP based and none of this is necessary.

I did it on my 2011.is that ok?

Well my car runs better all the way to redline now.

[fallrisk]

Originally Posted by williaty

What are your AF Learning #1 A through D values?

Hey williaty, not sure. Haven't invested in a tactrix cable yet but I've since fixed the issue and have pulled apart/reinstalled the airbox and intake multiple times and no longer have the issue!

I'm assuming there was a slight leak that I've since fixed.
(pls excuse the lack of cleaning and my car's true age showing LOL)


I've also since done a snorkus delete to see what would happen, and all I've noticed is increased noise above 3.5k/4k. What have been your findings on the snorkus delete, williaty?

EDIT: I've also finally removed the torque box mounts.. They were a ***** to loosen but came off so easily afterward. Sketchy times underneath my car with all that force I was pushing upward.

[williaty]

Originally Posted by fallrisk

I've also since done a snorkus delete to see what would happen, and all I've noticed is increased noise above 3.5k/4k. What have been your findings on the snorkus delete, williaty?

Jesus christ

This whole thread has been about why you CAN'T delete the Helmholtz resonator (snorkus).

[fallrisk]

Originally Posted by williaty

Jesus christ

This whole thread has been about why you CAN'T delete the Helmholtz resonator (snorkus).

Yeeeep, that's entirely my fault. Not too sure how I missed that part of your post/the thread. From a physics point, I find it hard to grasp that the resonator creates the effect as shown in your graphs (not doubting you, can't really understand how/why it occurs). I suppose that disallowing the resonation to occur increases the functional suction/vacuum and creates a stricter airflow in which the ECU isn't tuned for.

Out of all the posts I had read, I saw no one else really speculating this. Has anyone tried tuning against these MAFv spikes (except for TiC's fix for CAI/SRI)? In reality, at a physics standpoint the way I understand it, the resonator is simply acoustic with a slight disturbance in the effectivity of the intake vacuum which would explain the MAFv spike at lower RPMs. Through speculation, this is due to the fact that the air isn't sucked out of the resonator at lower rpms when installed, disturbing the flow of air until the vacuum hits a certain point (at the higher rpms) where the resonator is effectively turned into a part of the vacuum? This would explain the MAFv spike receding after the spike with the snorkus delete.. Guess I'll be throwing it back on.. That's probably also why cone filters create these issues with MAF intakes..'

I wonder what a cone filter -> straight tube + resonator -> MAF graph would look like in this case.. Could be an interesting thing. Sadly, these cars aren't really in the spotlight so it'd have to be on us old NA guys to try it. If I had more free time from classes/school, I'd love to be a guinea pig to try this out. Could be really interesting.

[williaty]

Originally Posted by fallrisk

From a physics point, I find it hard to grasp that the resonator creates the effect as shown in your graphs (not doubting you, can't really understand how/why it occurs). I suppose that disallowing the resonation to occur increases the functional suction/vacuum and creates a stricter airflow in which the ECU isn't tuned for.

No, it's nothing like you describe.

Without the Helmholtz resonator, the intake tract has a strong resonance at the valve opening/closing frequency of low RPM engine operation. This resonance causes the MAF sensor to record an erroneously high voltage. This voltage cannot be accounted for via MAF scaling (the table that shows the relationship between MAFv and grams of air passing the MAF sensor) because the erroneous MAFv reading during the resonance occurs legitimately at a higher RPM. If you alter the MAF scaling to correctly indicate the amount of air entering the engine during the resonance at low RPM, the scaling then badly under-represents the true amount of air entering the engine at non-resonant higher-RPM conditions. All the MAF scaling table can accomplish is to trade an extreme rich condition at low RPM for an extreme lean condition at higher RPM. This is why it is not simply tunable and the only software patch I'm aware of is the one I developed for TiC.

In reality, at a physics standpoint the way I understand it

No, you misunderstand Helmholtz resonators specifically and damped, driven harmonic oscillators in general.

[fallrisk]

Well, I've since finally got my milk jug back on, done some seafoam cleaning and did an ECU relearn for the first time since adding a WRX catback.. Seems just much smoother with the milkjug and there's definitely a noticeable bog from the richness spike running a milkjug delete.

Thanks to williaty for being tolerant of my stupidity and coming up with this sweet stuff.

[n00dl]

Is it possible to get a link to the intake pipe you all are using for the hybrid setup? I like the pipe Roke, rallyfan98, and fallrisk show in their pictures. I believe I'm a little too direct in my google searches

Thanks for the help guys! First time on the forum, it was a highly recommended search from a VW buddy of mine who even name dropped williaty. Your work is well known and the appreciation is real.

[fallrisk]

Originally Posted by n00dl

Is it possible to get a link to the intake pipe you all are using for the hybrid setup? I like the pipe Roke, rallyfan98, and fallrisk show in their pictures. I believe I'm a little too direct in my google searches

Thanks for the help guys! First time on the forum, it was a highly recommended search from a VW buddy of mine who even name dropped williaty. Your work is well known and the appreciation is real.

I got the "bolton premiere," carparts had it for cheapest during my searches. Their price beat out everyone on eBay and I can't complain.