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Old 09-07-2021, 02:15 AM   #1
SLO RU
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Default What kind of power do the 2015+ STi make

Wondering what kind of power the 2015+ STi can put out (safely) with the basic modifications without going to a bigger turbo. Exhaust, intake, tune, etcÖ

Trying to decide if I want to trade in my WRX for a new STi now, or just wait for the new 2022-2023 WRX/STi. I donít want to dump money into my current WRX and Iím over this car.


Thanks.
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Old 09-07-2021, 09:34 AM   #2
ntg44
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I'm going through this process right now. Honestly, it's not cheap, but the simpler you keep the parts list, the cheaper and more sense it makes. In my opinion from the research I've done and my experiences so far:

- Cobb complete flex fuel package (~$2500)
- Downpipe (price varies if you choose catted or not)
- Cobb Accessport ($600)
- 3 port EBCS (~$100)
- Custom flex fuel tune (varies)

Simple, no nonsense parts list that gets you in the ~335 hp/365 tq range on E85. Everything else is diminishing returns, and return per dollar isn't really there in my opinion. This setup will land somewhere between 4 and 5k all in and is plenty of fun for a car like this.

The rest (intake, exhaust, etc.) is nice and fun, but it's fluff. The only reason I changed exhausts at all is because I couldn't tolerate the stock exhaust drone, so I had one fabricated that fixed it. And I'm sticking with stock intake because I'm not really into the noisemakers anymore, at least on turbocharged engines. But I understand the appeal, so it's really limited to your budget and how far you want to take it. Personally, I prefer the least amount of parts replaced as possible.
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Old 09-07-2021, 10:44 AM   #3
K3rm1tth3fr0g
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Stock turbo youll be around ~350WHP/375WTQ on full E85 conversion.

The FA20 WRX can make 400WHP on the stock block on Ethanol.
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Old 09-07-2021, 11:30 AM   #4
benflynn
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Or open source and tactrix 200$
Flex kit 100$
Cai 200$
Injectors 2-500
Pump 100
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Old 09-07-2021, 03:08 PM   #5
SLO RU
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Quote:
Originally Posted by K3rm1tth3fr0g View Post
Stock turbo youll be around ~350WHP/375WTQ on full E85 conversion.

The FA20 WRX can make 400WHP on the stock block on Ethanol.
How?

What modifications would need to be made and how safe would it be?

I daily drive my car when Iím not riding my bike, I donít drive hard but I donít drive like a grandma either.. Iíd want it to be able to handle 1-2 pulls a few times a month without blowing up.

I asked about making 400hp in my 2018 WRX and everyone was telling me itís going to be a pain in the ass and not safe at all. So I figured Iíd try to upgrade cars before spending money on this car.
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Old 09-07-2021, 05:44 PM   #6
K3rm1tth3fr0g
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Quote:
Originally Posted by SLO RU View Post
How?

What modifications would need to be made and how safe would it be?

I daily drive my car when I'm not riding my bike, I don't drive hard but I don't drive like a grandma either.. I'd want it to be able to handle 1-2 pulls a few times a month without blowing up.

I asked about making 400hp in my 2018 WRX and everyone was telling me it's going to be a pain in the ass and not safe at all. So I figured I'd try to upgrade cars before spending money on this car.
The stock turbo is really good. You just need the parts to run an ethanol blend:

https://phatbottituning.com/2015%2B-wrx-suggested-parts

Go into the FA section

The highest stock turbo ethanol 2015+ WRX I have seen was 427WHP on E66

If I were you I would stay on the FA platform and throw some parts + ethanol at the car if you want have a good time on the street - It will be much faster than even a lightly modified STi.

And you really don't need the STi 6mt and the Brembos if you are staying on the street.

Last edited by K3rm1tth3fr0g; 09-07-2021 at 05:51 PM.
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Old 09-07-2021, 06:17 PM   #7
WRXnick16
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I'd wait for the FA24 in the 2023+ STI. My bet is a simple downpipe (j-pipe), ethanol sensor & flex fuel tune will easily net ~375-400+ whp depending on the dyno. Then you'll still get the STI drivetrain, Brembos & hopefully Recaros. No need to upgrade the fuel system because the stock injectors have plenty of overhead.

The EJ just doesn't respond as well to ethanol and basic bolt-ons as the FA. The FA24 will produce more torque and be more responsive (longer 86mm stroke, higher compression ratio, low mount twin scroll turbo, etc.). Not to mention, it'll also get better fuel economy as an added bonus.

Here's a pretty fair-ish EJ257 vs FA24DIT dyno comparison (same turbo, similar mods, same dyno, same tuner). Keep in mind that this is the FA24DIT engine from the Ascent SUV.. not whatever special bits the STI-tuned version may receive.



The FA24 dominates in area under the curve and makes more torque everywhere despite the old EJ having a slight displacement advantage. It has the potential to be a monster if Subaru doesn't ruin the rest of the car.

FA24DIT (from Ascent):
Power: 537 whp
Torque: 490 wtq (lb-ft)
Fuel: E56 blend
Boost: 22 psi
Displacement: 2387cc (2.4L)
Bore & Stroke: 94mm x 86mm
Bore/Stroke ratio: 1.09 (oversquare)
Rod/Stroke ratio: 1.5
Compression: 10.6:1
Effective compression: 26.5:1
Injection: Direct
Turbo: Low mount, twin scroll, ball bearing, 22 psi
Specific output: 225 WHP/L (~265 HP/L)
BMEP: ~41 bar (~242 lb-ft/L)

EJ257 ('19 STI Series.Gray):
Power: 463 whp
Torque: 448 wtq (lb-ft)
Fuel: E85
Boost: 26 psi
Displacement: 2457cc (2.5L)
Bore & Stroke: 99.5mm x 79mm
Bore/Stroke ratio: 1.26 (oversquare)
Rod/Stroke ratio: 1.65
Compression: 8.2:1
Effective compression: 22.7:1
Injection: Port
Turbo: Single scroll, ball bearing, 26 psi
Specific output: 188 WHP/L (~222 HP/L)
BMEP: ~36 bar (~215 lb-ft/L)

Turbo specs for both setups:
FP XR Blue 73HTZ ball bearing turbocharger
Flow rating: 57 lb/min
Compressor wheel: 52.6mm inducer/73mm exducer
Turbine wheel: 60.8mm inducer/54mm exducer
CHRA: Xona Rotor ball bearing
Turbine jousing: EJ is single scroll, FA is twin scroll

Last edited by WRXnick16; 09-07-2021 at 06:39 PM.
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Old 09-07-2021, 06:48 PM   #8
K3rm1tth3fr0g
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Quote:
Originally Posted by WRXnick16 View Post
I'd wait for the FA24 in the 2023+ STI. My bet is a simple downpipe (j-pipe), ethanol sensor & flex fuel tune will easily net ~375-400+ whp depending on the dyno. Then you'll still get the STI drivetrain, Brembos & hopefully Recaros. No need to upgrade the fuel system because the stock injectors have plenty of overhead.

The EJ just doesn't respond as well to ethanol and basic bolt-ons as the FA. The FA24 will produce more torque and be more responsive (longer 86mm stroke, higher compression ratio, low mount twin scroll turbo, etc.). Not to mention, it'll also get better fuel economy as an added bonus.

Here's a pretty fair-ish EJ257 vs FA24DIT dyno comparison (same turbo, similar mods, same dyno, same tuner). Keep in mind that this is the FA24DIT engine from the Ascent SUV.. not whatever special bits the STI-tuned version may receive.



The FA24 dominates in area under the curve and makes more torque everywhere despite the old EJ having a slight displacement advantage. It has the potential to be a monster if Subaru doesn't ruin the rest of the car.

FA24DIT (from Ascent):
Power: 537 whp
Torque: 490 wtq (lb-ft)
Fuel: E56 blend
Boost: 22 psi
Displacement: 2387cc (2.4L)
Bore & Stroke: 94mm x 86mm
Bore/Stroke ratio: 1.09 (oversquare)
Rod/Stroke ratio: 1.5
Compression: 10.6:1
Effective compression: 26.5:1
Injection: Direct
Turbo: Low mount, twin scroll, ball bearing, 22 psi
Specific output: 225 WHP/L (~265 HP/L)
BMEP: ~41 bar (~242 lb-ft/L)

EJ257 ('19 STI Series.Gray):
Power: 463 whp
Torque: 448 wtq (lb-ft)
Fuel: E85
Boost: 26 psi
Displacement: 2457cc (2.5L)
Bore & Stroke: 99.5mm x 79mm
Bore/Stroke ratio: 1.26 (oversquare)
Rod/Stroke ratio: 1.65
Compression: 8.2:1
Effective compression: 22.7:1
Injection: Port
Turbo: Single scroll, ball bearing, 26 psi
Specific output: 188 WHP/L (~222 HP/L)
BMEP: ~36 bar (~215 lb-ft/L)

Turbo specs for both setups:
FP XR Blue 73HTZ ball bearing turbocharger
Flow rating: 57 lb/min
Compressor wheel: 52.6mm inducer/73mm exducer
Turbine wheel: 60.8mm inducer/54mm exducer
CHRA: Xona Rotor ball bearing
Turbine jousing: EJ is single scroll, FA is twin scroll

Fair point but the FA20 is pretty capable as it is and he currently owns a car with one.
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Old 09-07-2021, 07:22 PM   #9
WRXnick16
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Quote:
Originally Posted by K3rm1tth3fr0g View Post
Fair point but the FA20 is pretty capable as it is and he currently owns a car with one.
True, but having owned a '16 WRX (flex fuel tuned) & '19 STI, the WRX's FA20 is easier to make power with, but the WRX lacks the driver engagement that the STI has (steering feel, rod-actuated shifter, brembo brakes, less understeer, etc.). Everything just feels tighter and sharper in the STI. It feels less mushy and more like a drivers car's (or as much as it can for a "compact" sports/performance sedan.

Power aside, I have no regrets upgrading from my '16 WRX to '19 STI. Even if the STI is slower and gets worse fuel economy.. it's more enjoyable and engaging to drive. I hope the next gen STI doesn't lose that. I wouldn't mind having a FA24DIT swap in my STI

The leaks of the next gen WRX aren't that appealing to me as it's looking more like a wilderness model with all of the black plastic cladding everywhere. Hopefully the STI is different.

Now days, it's so easy to get caught up in the horsepower wars and focus on power numbers and performance metrics. If you're a true car/driving enthusiast, you'll likely care more about the sensation that you get from driving the car as you won't always be doing 1/4 mile runs, 0-60mph launches or dyno runs. Those are mostly bragging rights. Back when I owned my AP2 S2000, I test drove a GTR on the road and around a track. I instantly knew it wasn't the car for me. It was ridiculously fast, but lacked the engagement and feedback of my very slow S2000. But this is what I personally enjoy about driving. If I didn't need a backseat then I'd buy a ND2 Miata because they're a blast to drive (the 2nd gen BRZ tS may be in my future). If I was in the search of power on a budget, I'd buy a Mustang GT (or Mach 1) and install a CARB legal supercharger for 700+ HP. Basically, decide what you're looking for in a car (and what you don't like about your WRX since you said you're "over it"), then go test drive and spend as much time in cars that you're interested in. Renting a car on Turo and spending a weekend with it is another great option so you can get some more seat time to see how you feel about the car.

Basically, don't trade in your WRX for a current gen STI if you're just looking for more power. The WRX wins in terms of power per $.

Last edited by WRXnick16; 09-07-2021 at 07:43 PM.
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Old 09-07-2021, 11:10 PM   #10
benflynn
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Is there now a FA pump that dosnt degrade with E85? Also, an ej with higher CR would compare better.
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Old 09-07-2021, 11:14 PM   #11
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I wonder how many 8sec or 1200hp FA there are out there
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Old 09-08-2021, 10:47 AM   #12
WRXnick16
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Quote:
Originally Posted by benflynn View Post
An EJ with higher CR would compare better.

I wonder how many 8sec or 1200hp FA there are out there
Sure, you could build an EJ with higher CR pistons but then it would also be more susceptible to knock at high boost levels without the aid of direct injection. You could also add a stroker crank to the build. And a bottom mounted, twin scroll turbo setup would also compare & perform better.. but Subaru didn't build that modern EJ for us. The EJ's basic design hasn't changed and is 20+ years old at this point. Technology & engine design have advanced a lot.

I agree, if you want a dyno queen or the faster drag car, the EJ is "easier" to get there at this point since it's been around for so long and has huge aftermarket support. But expect to spend at least $30k+ on the engine to reach those goals and have a shop/race team to perform routine engine rebuilds/refreshes. If those are your goals, a Subaru isn't the best car for you anyways. If you want an AWD monster, a GTR is a much better platform to start with.

The average Subaru enthusiast wants a practical, fast-ish, fun street car that's still reliable.. not a full blown drag car. The OP doesn't even want to upgrade the turbo.. so the FA engine is the better choice for simple bolt-ons. Show me a STI with the stock turbo and injectors that can push ~400whp.. it just can't happen. However, IMO the STI is the better all around package from a driving dynamics standpoint (I've owned both).

I'm not hating on the EJ.. in fact I'd choose the S-series EJ207 over the FA20 & EJ257. If Subaru & STI can mix & match parts from the BRZ to build an STI-tuned FA24DIT then I think we would have a winner. Ideally, it would come from the factory with dual injection, a higher flowing intake manifold & heads like the BRZ.. and of course a properly sized turbo & cams that could operate at higher RPMs like the BRZ. But I don't think that'll happen

Now that aftermarket ancillary port injection is available for the FA20DIT, there are more WRXs in the 600-800whp range pushing 9s in the 1/4. I look forward to seeing the potential of the STI's FA24DIT. Keep in mind, the EJ257's 2.5L has nearly a 25% displacement advantage over the FA20's 2.0L.

Last edited by WRXnick16; 09-08-2021 at 11:41 AM.
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Old 09-08-2021, 08:22 PM   #13
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Thanks for all the info. I def. have some thinking to do now, not sure what direction to go now..
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