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Old 05-02-2021, 10:55 PM   #1
SLO RU
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Join Date: May 2018
Location: iLLinois
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Default Question about newer STi and power they can make/handle

I have a 2018 WRX, so not familiar with the STi. I wanted to wait for the new one to come out but I am running out of patience, my questions are...

1) How much power can these newer STis handle safely?
2) What mods does it take to get around 400 HP?

I am not trying to build a rocket ship, just something more than what I have now. I'd like to get one around 400 HP, if it can be done safely, more.

Thanks.
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Old 05-03-2021, 06:35 AM   #2
hotdog
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The STIs haven't really changed in... well, a long time. The newer ones have 'better' internals, a carry over from the RA, but really, there's not a whole lot different since.. oh, 2004?

The tuning and technology has gotten 'better', and more refined; E85 is super simple, parts are plentiful and well researched, and there's not much 'new'; the platform is super old.

You're going to get 15 different answers, but ~360ish/400ish on E85 on stock turbo is 'realistic', with outliers from high reading dynos and kill-mode tunes being somewhere north of that.

This blog is fairly 'honest':

https://www.flatironstuning.com/blog...-a-stock-ej257

And this series has nice photos, anyways, and the summary is basically the truth.

https://dsportmag.com/the-tech/test-...ej257s-limits/

I personally am running E85, and am sitting at ~350/380, and the car is super fun and drivable. E85 really makes the whole car different, so if you're in a location that can get it, 100% look into that.
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Old 05-03-2021, 06:42 AM   #3
murrdogg24
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Actually the current EJ257 hasn't changed much since dual AVCS was introduced in 2008. Most people overlook that when they say it's the same engine from 2004. Yeah you can make easy power on E85 but be prepared to fill up the gas tank about twice as often, you'll be getting like 8-10 MPG. So what you'll need is a flex fuel kit, fuel stumble fix, injectors and fuel pump, aftermarket boost control(maybe) and tune and you can get close to 400.
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Old 05-03-2021, 06:57 AM   #4
hotdog
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True. Changes have been made over the years, but by and large the 'max power output' is fairly static; the tech and the tuning has just gotten 'better'.

https://www.igotasti.com/threads/ej2...present.13132/

And yes, E85 is hilariously inefficient, but if the stars align and you can make it 'work', both financially and 'how often I visit the gas station', it's well worth it.
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Old 05-03-2021, 10:46 AM   #5
pigboat_2
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8-10 mpg? I'm running ID2k's and like 600+ hp and I still get 15+ mpg on E85-E90. Get your foot off the floor every once in awhile geez lol

But yeah the info is accurate. Go FBO and E85 on the stock turbo and your result will be decently reliable and will make good power for the money.

In my experience of low-reading dynos you won't really be that close to 400, more like 330 on the stock turbo, but it's all relative.
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Old 05-03-2021, 11:48 AM   #6
undyjr
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Sorry, wrong thread.

Last edited by undyjr; 05-03-2021 at 11:51 AM. Reason: wrong thread
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Old 05-03-2021, 04:26 PM   #7
hotdog
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Quote:
Originally Posted by pigboat_2 View Post
8-10 mpg? I'm running ID2k's and like 600+ hp and I still get 15+ mpg on E85-E90. Get your foot off the floor every once in awhile geez lol

But yeah the info is accurate. Go FBO and E85 on the stock turbo and your result will be decently reliable and will make good power for the money.

In my experience of low-reading dynos you won't really be that close to 400, more like 330 on the stock turbo, but it's all relative.
Around town my MPG is... bad. Like hilariously bad. Highway might be 15ish, but most long trips I'm back on 93 anyways.

I'd say stock turbo + E85 is worst case scenario for fuel efficiency; if you're running 600HP+, you're on a bigger turbo = more RPM for spool, etc. I can spool damn low on stock turbo = more fuel = bad MPG :P
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