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Old 06-02-2021, 08:03 PM   #1
anotherfrostback
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Member#: 524583
Join Date: May 2021
Default Fuel system upgrades 2018 STI

Well I have spent quite a bit of time reading other threads and don't feel like I am any further ahead. I am new to Subaru but have experience with building other brands.

I have come to a cross roads on upgrading the fuel system so I am hoping for a bit of advice from people more familiar with EJ's. I have assembled most of the parts and am getting ready to install and tune soon and trying to decide if any fuel system upgrades are required/recommended. I do not have plans to upgrade the turbo.

Mods:
Cobb Accessport
Cobb catted downpipe
Nameless UEL Headers and up pipe
Tomei 3" ti Catback
Grimspeed CAI
Cobb boost controller.
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Old 06-02-2021, 08:10 PM   #2
heiche
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Member#: 400179
Join Date: Aug 2014
Vehicle:
2009 wrx

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if it were me i would only consider upgrading the fuel system if going e85 and/or doing a turbo upgrade. at that point bigger fuel pump and injectors would be part of the plan.
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Old 06-02-2021, 08:12 PM   #3
K3rm1tth3fr0g
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Member#: 508105
Join Date: Nov 2019
Chapter/Region: NWIC
Location: Greater Seattle Area
Vehicle:
Link G4X flex tuned
02' EJ205 20G 6MT wagon

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Quote:
Originally Posted by anotherfrostback View Post
Well I have spent quite a bit of time reading other threads and don't feel like I am any further ahead. I am new to Subaru but have experience with building other brands.

I have come to a cross roads on upgrading the fuel system so I am hoping for a bit of advice from people more familiar with EJ's. I have assembled most of the parts and am getting ready to install and tune soon and trying to decide if any fuel system upgrades are required/recommended. I do not have plans to upgrade the turbo.

Mods:
Cobb Accessport
Cobb catted downpipe
Nameless UEL Headers and up pipe
Tomei 3" ti Catback
Grimspeed CAI
Cobb boost controller.
You gain some headroom for knock and over boost by upgrading injectors but your tuner should be able to set you up on your current config.

But always try and listen to your tuner.

Edit: I assumed you already had a pump, you'll def need a pump.

Last edited by K3rm1tth3fr0g; 06-02-2021 at 09:49 PM.
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Old 06-02-2021, 09:17 PM   #4
Haevn
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Member#: 495950
Join Date: Jan 2019
Chapter/Region: South East
Location: Augusta, GA
Vehicle:
2011 WRX
WRB

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fuel pump is a must, not so much for injectors
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Old 06-09-2021, 08:20 PM   #5
Holly18Sti
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Join Date: Jun 2021
Location: Pittsburgh
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2018 STI
Black

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What tune do you plan on using pro or e?

I’m finally starting to modify my 18 and looking forward to what numbers you make with these parts.
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Old 06-09-2021, 08:36 PM   #6
KillerBMotorsport
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Member#: 198281
Join Date: Dec 2008
Chapter/Region: MAIC
Location: Virginia
Vehicle:
2005 WRX/STi
WRB of course

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I would add a fuel pump to the list for sure.
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Old 06-15-2021, 02:00 PM   #7
ntg44
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Member#: 510765
Join Date: Jan 2020
Vehicle:
2020 WRX STI

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Related question...

I recently got my 2020 STI custom dyno tuned, made 290/306 wheel with the following mods:

Cobb AP
Cobb catted DP
custom 3 inch exhaust
3 port EBCS
Grimmspeed top mount intercooler

I told the tuner to cap the mid range because I don't like mountain shaped torque curves, and also told him to take it easy on fuel system. Ended up with a nice flat torque curve from 3500-5700 RPM before tapering. But If I'm being completely honest, I was a bit underwhelmed with the end result. It's "okay", but leaves me wanting about 20% more after driving on it for a few weeks.

My question is, how much is there to gain at "stage 2" by adding the pump and injectors? Is it even worth the trouble, or does it really only make sense at flexfuel/e85/larger turbo?

Thanks in advance.
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Old 06-15-2021, 02:46 PM   #8
K3rm1tth3fr0g
Scooby Specialist
 
Member#: 508105
Join Date: Nov 2019
Chapter/Region: NWIC
Location: Greater Seattle Area
Vehicle:
Link G4X flex tuned
02' EJ205 20G 6MT wagon

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Quote:
Originally Posted by ntg44 View Post
Related question...

I recently got my 2020 STI custom dyno tuned, made 290/306 wheel with the following mods:

Cobb AP
Cobb catted DP
custom 3 inch exhaust
3 port EBCS
Grimmspeed top mount intercooler

I told the tuner to cap the mid range because I don't like mountain shaped torque curves, and also told him to take it easy on fuel system. Ended up with a nice flat torque curve from 3500-5700 RPM before tapering. But If I'm being completely honest, I was a bit underwhelmed with the end result. It's "okay", but leaves me wanting about 20% more after driving on it for a few weeks.

My question is, how much is there to gain at "stage 2" by adding the pump and injectors? Is it even worth the trouble, or does it really only make sense at flexfuel/e85/larger turbo?

Thanks in advance.

You will gain mostly safety when upgrading fueling but the gains from E85 are BIG.


I would look into ethanol, pump and injectors.
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Old 06-15-2021, 03:09 PM   #9
ntg44
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Member#: 510765
Join Date: Jan 2020
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2020 WRX STI

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Quote:
Originally Posted by K3rm1tth3fr0g View Post
You will gain mostly safety when upgrading fueling but the gains from E85 are BIG.


I would look into ethanol, pump and injectors.
Okay, thanks for the feedback. Time for some research
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