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Discussion Starter #1
I'm grabbing the parts and the new filter. Surprisingly the parts are more cheaper than the standard STI stuff.

It seems you need about 4-5 parts.

1. Top of air box
2. bottom of air box
3. The triangle funnel thing that goes to the front
4. Clamp
5. Filter

Not listing them here since you can find them on parts.subaru.com

My worry is if I need to tune the intake or not. I don't know if this gives some gains but it's cheap enough that I'll get it. I haven't protuned yet so I'll probably get this on while I get a tune sometime in June or so.
 

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If the MAF is a different diameter you will need a tune for sure. It seems like that is not the case, based on the parts you listed...
 

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Discussion Starter #3
If the MAF is a different diameter you will need a tune for sure. It seems like that is not the case, based on the parts you listed...
Is that why those AEM and Cobb Intakes need tunes because it's larger diameter as well as the filter cone?

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HKS and Injen are a couple of suppliers that make a complete kits that replace the filter box, the scoop to the front grill area and the MAF Tube, and have a factory appearance but are larger. I doubt you'll need a tune with the Subaru STI Type RA airbox on the a 2015-2018 base EJ, but you would probably benefit from one with respect to throttle response. The RA has a different ECU but it also has a lot more changes to it than the Base STI's that the ECU has been optimised for....its a lot more than just an air box change....so changing just the air box on the base 2015+ STI's to the RA parts shouldnt cause any driveability issues.
 

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What I can say is, if you do increase the airflow; the ECU may not allow you to reap the benefit of the higher flowing intake. Until you tune it.

I've been doing a test on my STI by replacing the stock OEM filter to BMC panel filter.

It answers a few things:

1. No it doesn't harm my engine. Not a knock retard or knock correction on log pulls (3rd gear, 2krpm to 7100rpm). Long term wise, no idea.

2. Boost earlier, and just a tiny bit more across the whole rpm range, resulting in stronger low to mid pull. Indicative of higher flowing BMC filter perhaps? Possible.

3. But ECU delays the timing advance post max boost, resulting in sluggish mid to top rpm. No good.

4. MAF g/s confirmed more air low to mid, but reduced air mid to high.


Not trying to start another debate of panel filter, just reporting my finding as I was curious about it. I did two pulls, and both pulls shows consistent reading. Then I just compare it with OEM panel filter log, and trace it from there.

Will I benefit if I tune for; possible.

So if I add this Type RA airbox, I am expecting it may be necessary to have the car to be tuned for it to reap the benefit of the higher flowing airbox (I assume it is). And may aswell throw in Sprint Filter along with it.
 

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Discussion Starter #9
What about when the OEM filter is very dirty, the flow is definitely alot less than a brand new filter, yet ECU can compensate.

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What about when the OEM filter is very dirty, the flow is definitely alot less than a brand new filter, yet ECU can compensate.

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Yes, you are right.

And that is why it is important to have the car tuned with brand new air filter. That's what I did prior to tuning, including new oil and spark plugs. Did a compression check too, as I do not want to ends in blaming game.

In this way, at least by my logic, the amount of flow the brand new oem panel can deliver is what the ecu recognized during tuning for max power.

That being said, a dirty air filter needs to be an awfully dirty to the point of filth to be less effective. But you know, to be safe, just use brand new air filter before tuning.

So yeah.
 

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Any performance gains?
I didn't take it to the dyno, but I do not think there is any gain happening in my car with BMC filter replacing the OEM filter. Loss of power is what I felt.

I don't say the BMC air filter is worse than OEM, on the contrary I think it flows so much better the ECU just does its thing to protect the engine. Not all car's ECU behaves this way though.

Oh, speaking about high flowing filter here is an independent test results done by Trinity University in Wales regarding high flow air filter:



But anyhow, it was a fun test for me.

And of course I could be wrong. So I encourage you to do your own testing too.
 

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My worry is if I need to tune the intake or not.
Monitor your AFR with a wideband and you'll have your answer. That's the only way to know for sure.

I don't say the BMC air filter is worse than OEM, on the contrary I think it flows so much better the ECU just does its thing to protect the engine. Not all car's ECU behaves this way though.
This ECU doesn't behave that way unless it senses knock.
 

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I just put mine in my 09, I cut the front portion of the airbox and shoved it back inside the box allowing it to fit, will see if it helps any! Only downside for these questions is when I'm o the dyno next will have 20g with larger fuel system
 

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I just put mine in my 09, I cut the front portion of the airbox and shoved it back inside the box allowing it to fit, will see if it helps any! Only downside for these questions is when I'm o the dyno next will have 20g with larger fuel system
Which front portion? Do you have pics? :D
 
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