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Old 01-25-2022, 08:45 PM   #1
Scooby Newbie
Member#: 528542
Join Date: Jan 2022
2015 STI

Default Full exhaust system/Intake/Fuel injecters? (NEWBIE)

Hi all, I have recently become the owner of a 2015 sti. The car is basically brand new and is fully stock with 27xxxkms.

Little disclaimer I am very new to car modifications and have little next to no experience so I am looking to learn along the way. Any info or experience you guys can pass on is appreciated. So here are some questions.

I want to know if it's possible to install a full exhaust system and an intake without diving into upgrading fuel injecters etc or if I can only install or an exhaust system or intake before upgrading anything fuel related.

Giving reasons to why I should or should not would be very helpful also
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Old 01-26-2022, 08:51 AM   #2
Add Lightness
Member#: 13699
Join Date: Dec 2001
Chapter/Region: NESIC
Location: Hopkinton, MA
2021 Building
It Better


You can add a cat back, which will increase noise and add 0 hp, but it can be done with nothing else.

If you add an intake, it will add 0 hp but increase noise and you WILL have to tune for that. This can either be done by buying a Cobb intake and a Cobb Access Port and choosing the appropriate off the shelf tune that comes with the AP.

If you plan to add either a high flow cat with your exhaust or a catless downpipe, then again, you will need a tune. For the high flow cat, if you buy a Cobb, you can buy a Cobb Access Port and choose the appropriate tune that covers this. For a catless downpipe, you would have to get either an off the shelf or dyno tune from one of the independent tuners. I know for example, Bren Tuning offers both and has quality products. There are others, of course, but I'm in Bren's area and have known him since the Fred Flintstone days when he just balanced boulder wheels on cars. *I just remembered....because the EPA is cracking down on tune providers and tune shops, it's possible that nobody will tune anymore for catless down pipes. They are illegal to remove and the EPA has an old $10k fine for doing this. Shops have been hit with fines well over 10 times that and have had to cease tunes that would not pass state emissions requirements.*

If you choose either an intake or catless exhaust with no tune, price out a new engine because Subarus do not do well with these and you will lunch your engine. Also, look into the state requirements. California won't allow either of these without a CARB sticker and I hear that they have portable truck shredders and will shred your car on the spot. (I just made that up). If you remove the cat or put in a high flow cat, you could generate a P0420 code without a tune to avoid it (cat converter efficiency below spec) and if you're in a state like mine (Massachusetts), you will fail inspection.

Intake and fuel system upgrades usually come after you up your turbo or if you go to E85 fuel.

Keep in mind that real cars are not Gran Turismo and you can't just add parts to Subarus without properly planning and addressing the tune level.
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Old 01-26-2022, 10:36 AM   #3
Scooby Specialist
Member#: 508105
Join Date: Nov 2019
Chapter/Region: NWIC
Location: Greater Seattle Area
Link tuned 02 WRX
EJ205 20G-XTR JDM 6MT E85


After my experience with them, I would avoid off the shelf tunes.

If you want a turboback exhaust and an intake, you need tuning. And a protune is better in practically every way than a canned tune (unless your tuner is an idiot).

But good luck getting a protuner to touch your car in 2022 with a catless downpipe.
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