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Old 02-21-2013, 01:58 PM   #1
Scooby Specialist
Member#: 316928
Join Date: Apr 2012
Location: TX
2012 STI limited

Question Drop in pistons for 2012 STI

Hello fellow nasiocers!

First off, please forgive my noobishness. I have read the piston FAQ's and most of the manifesto threads on here. I have learned a great deal about these cars but my knowledge of built motors is, admittedly, pretty low.

I am currently stage1 with sf intake, but I have quite a few boltons sitting in my living room ready to be installed. I am getting ready to take the plunge to stage 2+ and REALLY forgo my power train warranty.

My goals are for a 350 whp RELIABLE STI. As such, I am considering doing forged pistons before I do this. It seems that stage 2 on these cars really stretches the limits of reliability on the pistons. I want a fairly quick car that will last for many years and miles to come.

The rods and crank seem to be ok at the power levels I desire, but there is no denying cast pistons are the weak link. I am consdidering purchasing a nice set of standard size "drop in" pistons. ( cosworth , weisco, or CP). I would rather spend 1500 now, than 5k later , if you get me.

According to the piston FAQ, forged pistons require a bit more clearance, so I am assuming I will need to hone the cylinders accordingly? AM I correct in this? Please chime in here. Will the amount of required clearance vary from piston to piston? IE clearance for the cossies may be different from clearance requirements for weisco's?

Also, do I need to worry about having everything rebalanced and possibly blueprinted? I love my car, and am willing to spare no expense to do it right. I just would like to know what you guys suggest for this?

Is just boring the cylinders and dropping in new pistons sufficient, or do I need to go the extra mile to ensure great reliability?

Thanks in advance for your insights.


Well I just called then one local shop that does STI motor builds. The quoted me 2500 in labor for dropping in the pistons and the honing. Is this reasonable? I feel like I could spend that much ( maybe a bit more) and get and get a new shortblock with the pistons already in and pay my subaru tech buddy a few hundred just to install the block.
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Last edited by StackSmasher; 02-21-2013 at 02:13 PM.
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Old 02-21-2013, 08:23 PM   #2
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Member#: 327538
Join Date: Jul 2012
Chapter/Region: MAIC
Location: La Plata MD
2012 WRX (307/344)


Thats an appropriate price with engine removal and teardown. There is no guarantee in reliability, but forged pistons would theoretically make your car much safer and reliable at 350whp, and likely a little more. Yes, you are correct, you can find assembled shortblocks with pistons, rods, etc, in that price range - but still need someone to install it for you.

Best lf luck
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Old 02-21-2013, 08:38 PM   #3
Papi Chulo
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Chapter/Region: SCIC
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Why not run the motor until it pops? No sense in dumping tons of money into a motor when you could probably enjoy a safe 350whp sti for a year to several years?
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Old 02-21-2013, 09:14 PM   #4
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Location: TX
2012 STI limited


Originally Posted by godfather2112 View Post
Why not run the motor until it pops? No sense in dumping tons of money into a motor when you could probably enjoy a safe 350whp sti for a year to several years?
agreed. I spoke with another tuner who suggested exactly this. he said if I crack a ringland I have to go through the same process to fix it anyways so I may as well wait and do the build afterwards.

thanks for the feedback guys.
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Old 02-21-2013, 09:30 PM   #5
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Location: south nj
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+2 for rocking the stocker if you only plan to go STG2. Once you get the money, buy a new forged short block and sell your stock short block while its in good condition to offset the cost.

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Old 02-21-2013, 10:38 PM   #6
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2004 Forester XT


+3 on keeping it stock for now. My car made it to 225k miles before I cracked a ring land. I was pushing an APS SR50 which is 30r territory with other mods. Fix it when it breaks. Which it will. A good tune will buy you more insurance than forged pistons IMO
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Old 02-21-2013, 11:26 PM   #7
Irv Weissmanhowerton
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Location: Phatbotti
30r E85 sti 450+whp


your "built" motor might not be as reliable as your stock, 350whp isnt asking much of it, many have done 450-600whp on it for quiet some time

make sure you pick someone who is great on clearances, balancing, using torque plate honing
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Old 02-22-2013, 12:08 AM   #8
Flat 4 Motorsport
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The only thing to take into consideration is that if you run it till it blows up, what else are you taking out in the process?

Cylinder heads are expensive!

Head work is expensive, so crack a ringland and catch it quick enough and no real issues to be had hopefully. You should be able to hone the block out.

But bearings are not so forgiving so just keep that in your mind.
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Old 02-23-2013, 01:57 PM   #9
Scooby Newbie
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Join Date: Aug 2011
Location: Seattle, WA
2007 STi


Somewhat related question: how exactly would you catch a broken ringland? Is it just the normal symptoms (smoke and/or oil consumption)?
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