Building a short block; 2010 STi
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This is a discussion on Building a short block; 2010 STi within the Builds forums, part of the Tech & Modifying & General Repairs category; Hey everyone, recently my 2010 STi took a poop on me. Had some misfiring, put in new spark plugs, continued ...

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    Building a short block; 2010 STi

    Hey everyone, recently my 2010 STi took a poop on me. Had some misfiring, put in new spark plugs, continued misfiring. Did a leakdown test and got 80% leak on cyl. 2 and 40$ on cyl. 1. I was convinced it was ringlands, so I pulled out the engine in my driveway and brought it over to my friend's shop. We fully disassembled the engine, and behold, piston #2.



    Piston #1 had one chunk of ringland easily come out as well, and #3 had a few hairline cracks and a chunk missing, and #4 had just a small piece broken.

    I am now on the quest to rebuild the shortblock. I'm aiming for durability. I know everything will break at some point, especially with modified engines, but at this point I'd rather have more durability than power. I only had an intake, downpipe and exhaust and a dyno tune, with 330whp on the shop's Mustang dyno. I don't plan on making over 400whp anytime soon, but will eventually. I want my block to be as reliable as possible, while still making decent power.

    I've done a lot of research, and it seems rather expensive to buy a Cosworth short block, which was what I was considering. Does anyone know if you can send them your shortblock to avoid a core charge? My block is still in great shape (only 24k miles) and I don't need a brand new one. I've also read that it would seem to behoove me to have my block built by the same person that will be tuning it, that also provides a warranty, so their won't be any blame being passed around if and when it does break. So that brings me to another question, are there any reputable tuners/engine builders near the Philadelphia/Tri-State area? I'd rather not have my car need to go 5+ hours away to be tuned, unless this tuner/engine builder is godlike with Subaru motors.

    If I supply the parts and have someone build it or doing myself, I was thinking Cosworth pistons, and definitely Manley Turbotuff Rods. Probably Manley bearings as well. That's what I'm doing at the minimum, unless there are some other parts I can swap into the shortblock to increase durability. Also keep in mind this will be my dailydriver, however I don't mind if it's "not comfortable to DD" (I'm most likely doing a stage 4 six puck clutch).

    I'm not really looking for a specific power number; I was comfortable with the power it was making when it broke. I just want it to be more durable, and be able to handle the power when I do some more things to it down the road. Thoughts?

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    zax
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    Cosworth certainly produces quality product, but I'm not sure it's worth the price point. I'd suggest finding a reputable local builder to build your current block. For durability, use a 4032 alloy and not a 2618 which will make ends meat out of cylinder liners in about 50k miles. If there's nothing wrong with your bearings, this could be as easy as dropping in a set of 4032 pistons and calling it a day.
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    The rod bearings have some scoring so I'm going to replace those as well.

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    zax
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    Quote Originally Posted by AnthonyP View Post
    The rod bearings have some scoring so I'm going to replace those as well.
    Good idea... Subaru isn't known for choosing the best bearing materials.
    2015 CWP WRX STi ... But how did I get roped back into an EJ motor?!
    Zax's utterly unimaginably stock 2015 STi build thread
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    Since the engine is out, I'd recommend installing a KillerB oil pickup and windage tray as extra precaution. Wouldn't want to spend all that money and time to have a oiling problem cause more damage.

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