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Old 10-24-2020, 12:45 AM   #1
19transam81
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Join Date: Nov 2014
Location: Howell, Mi
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2011 STi
Plasma Blue

Default Doing headgaskets, can I do pistons too?

Hi team,

So I知 doing head gaskets and a bit of performance parts on my sti 2011. I知 thinking about doing some Manley forged pistons But I知 not sure how to go about it. My engine has 82k on it, stock pistons look prettty good, but I知 going e85 flex kit, bigger TMIC, EWG, TGV delete, air pump delete, EBC,fuel injectors and pump. Currently have intake, ELH, catless downpipe, catback. Can I just gap the rings, check clearance and drop in the new pistons? Or do I need to take the block in and get it honed and cross hatch? Thanks in advance for all of the advise.
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Old 10-24-2020, 08:02 AM   #2
snow_bound26
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Chapter/Region: Tri-State
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2005 92x Aero
Blue(retired�ȸ

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You are asking questions that need to be answered by a machinist. What determines whether you need any additional work done has to do with the condition of the cylinders; are they out or round? Is there scarring on the walls? Things like that. Can you just slap some pistons in? Sure. Will it have reliability? Who knows.

Why are you doing the HG? HGs aren't typically an issue with these cars unless you've over heated the engine. And if you've done that, then I personally would just slap some pistons in. When you take the heads off, it's a good idea to make sure the mating surfaces are flat. You could have a machinist measure the cylinders at that time and make a decision.
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Old 10-24-2020, 11:33 AM   #3
Blackfin
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Location: Ontario
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2010 STi
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Quote:
Originally Posted by 19transam81 View Post
Hi team,

So I知 doing head gaskets and a bit of performance parts on my sti 2011. I知 thinking about doing some Manley forged pistons But I知 not sure how to go about it. My engine has 82k on it, stock pistons look prettty good, but I知 going e85 flex kit, bigger TMIC, EWG, TGV delete, air pump delete, EBC,fuel injectors and pump. Currently have intake, ELH, catless downpipe, catback. Can I just gap the rings, check clearance and drop in the new pistons? Or do I need to take the block in and get it honed and cross hatch? Thanks in advance for all of the advise.
You're definitely going to want to break the glaze on an engine with 82K. If you don't, the new rings would never seat properly.

I agree with snow_bound: Before removing the OE pistons I'd take a number of bore diameter readings (inline and perpendicular to the crank axis and at several depths) to get an idea of taper and out of round to see if it's worth thinking about new pistons and rings in old bores.

What are your boost and power goals? Something to think about is to remove the OE pistons and to carefully regap the compression rings to open up the endgaps a bit and then reinstall everything. I personally believe that one of the biggest weakness of the EJ257 and the thing that leads to the majority of ringland damage is that Subaru used a very tight ( < 0.010") gap on the top ring. When you turn the wick up, the ring gaps closes due to heat and then seizes to the cylinder wall momentarily which leads to damaged ringlands. I think you could open that gap to more like 0.018" to alleviate that risk without incurring too-high a blowby penalty.
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Old 10-24-2020, 12:33 PM   #4
19transam81
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Yes the reason for doing the head gaskets is they are blown. The car pukes coolant out of the over flow, will start to get hot on the daily with the thermostat in, currently running no thermostat and you can add coolant to it at the end of the day just fine, but takes a half gallon. white smoke out the exhaust... no visible leaks so, I***8217;m guessing it***8217;s head gaskets? But it***8217;s my summer car so this is my winter project, getting started now.
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Old 10-24-2020, 12:47 PM   #5
Markopolo400
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I wouldn't put new pistons in unless you hone the cylinders to break the glaze as stated above, if you don't theres a chance you run into burning oil issues.

The problem is you would need to split the case to properly hone/clean the cylinders. At that point you might as well rebuild the bottom end while you're in there too.
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Old 10-24-2020, 05:11 PM   #6
HunteX
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You can take this with a grain of salt, however I've been talking to some people about what is necessary for a reliable daily when you change out your rods and bearings or do an overhaul: get a machinist to do it. When you slap it all back together without taking into consideration what gaps/spacing at greater than thousands of an inch do at 4, 5, 6 and maybe even up to 7k rpm you'll have a bad day, sooner than intentioned.
If you're opening the bottom end, do it right.
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Old 10-24-2020, 05:59 PM   #7
19transam81
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Thanks for all of the advise guys. I***8217;ll get with a machinist and get all of the details worked out.
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