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$Cost to make reliable 400 whp 2017 STI?

109385 Views 53 Replies 14 Participants Last post by  XJman
I'm thinking about buying a new 2017 STI. I'd really like it to make more power but would not want to have to worry about something going wrong since the warranty will obviously be compromised. So if I wanted 400 wheel horsepower or more what's the best safest route and how much would it cost?

I know all the basic parts evolved when tuning these cars for more power. But I want reliable power. So aside from all the bolt-ons like downpipe, upgraded fuel pump, exhaust, injectors, blah blah blah etc etc.

For reliability would it be necessary for forged pistons and a closed deck block? Or would the pistons be good enough? And what would the typical cost be for 400hp? I know for 300hp to the wheels stage 2 it's about $2900..
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If you don't mind me asking, why not buy an Evo X?

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Well i never liked the style of the Evo and there being discontinued. Plus the last year one the interior is horrible. Even tho the engine stock pistons are a weak link in the Subaru the drive train is way better then the Evo.
You will spend far less money making the Evo fast. End of story.

I don't understand you.

First you want a car that is fast enough to run mid 12s in the quarter. When I explain to you that there are far better cars than the STI for drag racing, you get defensive. Now you're asking about 400whp which will put you into the 11s if tuned on some dynos. If you like the STI, why not just buy it instead of asking all these damn questions?

If you truly are torn, please consider listening to the logic here.

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If you want 400whp, here:

  • ID1000 Injectors
  • Walbro 255lph pump
  • GTX3572R rotated manifold turbo
  • EWG
  • Killer-B ELH + rotated EWG UP (does this exist yet?)
  • E85 flex-fuel kit
  • Tuning solution (obviously)
  • TGV deletes
  • Parallel fuel rail mod
  • IAG fuel damper kit
  • Snow performance Water/Meth injection (you'll need all the det-resistance you can get)
  • Catless DP
  • Speed-density conversion
  • Killer-B Oil pan, baffles, and pickup (you'll need the extra oil capacity for cooler oil temps)

That should make 400whp on most dynos. The motor may last 100,000 miles or 1,000 miles. At these BMEPs, the motor could go at any minute.

Sure, you could build the motor for another $8,000-10,000 and it MIGHT last another 50k miles, but built motors rarely last as long as stock OEM motors.

At the end of the day, you might have an Impreza that cost you $65,000 and resells for $25,000. Or you could have a $40,000 Camaro SS (with 400+whp mind you) that resells for $38,000.
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Some reputable builders like IAG offer what they call a "drop-in piston" program that strengthens the primary failure point of the EJ257.

They take a brand new OEM engine and replace the OEM pistons with a set of forged aluminum pistons leaving the rest of the rotating assembly alone. The crankshaft and rods are quite strong from the factory, so this setup MIGHT make a reliable 400whp motor feasible. Or it may not. The benefit to this program is that block does not need to be split open. A program like this requires an almost new motor with factory cross-hatching since a bore-hone isn't practical with the rotating assembly in place.

This program typically costs between $2500-3000 so it is much cheaper than a full rebuild. If you want to do this properly, look for shops that will do a "Hot torque plate" piston installation whereby a plate is torqued to the block and the block is heated before the piston is installed. This process significantly reduces clearance-related failures.

If you value the life of your block, stay away from 2618 alloy pistons. These slugs will make short work of your OEM ductile iron sleeves. For a light build, 4032 pistons are far more practical. Good luck.
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Regardless, the 4B11T is a much better platform for reliable power compared to the EJ257.

Both motors can support similar torque in OEM form, but the 4B11T will produce approx. 15-20% more power for a give torque output.
Well its sounding like its not a good idea to try and increase the power in the STI. I love the car and the idea of having performance and AWD. But it may be sounding like it wont be enough performance. I get mixed signals because theres so many different opinions on this subject. Even when you look up opinions from tuners and builders advice like Crawford out in California and other reputable places they talk like the weakest link and problem really isn't the EJ motor at all. They say the real issue and cause of failer in these engines is people buying online tunes or taking it to a tuner that really isn't good at tuning these cars. And when that happens the EJ motor does not run right because it either runs lean or has knock and other issues which cause the rings to fail. According to them if its done right and the ECU is tuned right it will last as long as a stock engine!
I 100% agree with your assessment.

The biggest challenge is indeed improper modifications and bad tuning practices... particularly by tuners that are unfamiliar with the EJ platform.

That being said, your post is asking what it will take to maintain reliability while increasing the power output by 75%. That's a tall order. I truly believe that the issues with the EJ257 are generally over-hyped... a product of a very vocal community and the prevalence of a metric crapton of performance parts (having a platform around for 25 years tends to do that). Even still, there are limits and increasing the output 75% will most certainly reduce reliability.

If you want power and AWD, the Evo platform really is the superior choice.
With that said from what ive heard the Evo has the stronger engine to mod but the Subaru STI has the stonger trans and drivetrain. So if thats the case its kinda like pick your poison. Do you want to have to build the engine more on the STI and have a strong drivetrain or have weak drive drivetrain on the Evo but it has a strong engine!?!? Either car you would have to build something up.
Yes, I agree. It is a "Pick your poison" situation if you are shooting for more than 1000whp.

For "medium builds," the Evo is far cheaper to modify. The transmission itself is not the weakpoint, but the transfer case and AYC will need reinforcement over ~600wtq. The boxer motor will always be more expensive to build up compared to an inline-4.

Theres an article in Super Street Magazine online called The truth behind the Subaru EJ series engines- Tech Knowledge. Its a good read. Very reputable Subaru builders weight in on the EJ engine! Its a good read. Look it up..
I know, I've read it. I've been an active community member for roughly a decade.
I know you are very focused on power. May I ask why?

Weight is just as important and the Challenger you currently own is roughly 25% heavier.
You should consider a B8 Audi S4

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Plus it's available in 6MT or DSG

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Just an FYR.

The STI is nowhere close to a rally car. The "heritage" to which you speak is nothing more than a superficial resemblance to the body shape. This is simple marketing at best.

If you really wanted to throw "Rally heritage" into the mix, Audi has had a far more effective rally campaign over the years compared to Subaru.

Not to sound brash, but I've said it before... if you like the STI, by all means: buy one! I've been very happy with mine. But you are asking for a lot of mutually exclusive things here...

"I want 400whp, can the STI take it?" - The Evo or S4 are better platforms
"I don't like those other cars because [insert superficial reason]"

You have to let go of something here.... either that the STI is an effective drag platform or that somehow Subaru's campaign in Rally (which ended over a decade ago) is meaningful in any way other than as a marketing tool.

ADDENDUM: I'd also be much more pleased with my STI if Subaru offered the EJ207 here in the states. The EJ257 is just so.... meh.
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Have you ever wondered where all the Lancers went? Where are they lately?
I always assumed "into concrete retaining walls" -- the same fate as all of the SRT-4s.
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The Evo never sold in great numbers compared to contemporaries. Evo X numbers were just as low as previous generations, just the production run was much longer.

And it makes sense. The STI has always made a passable DD, but the Evo just sacrificed too much. When you live in that territory, there are more suitable options for a dedicated "fun car."
Pick whether you want to be Ridetillidie or Cole F. and let me know. I'll close the other account.
Too late. I made the decision for the poster.
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