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Old 07-19-2005, 10:41 PM   #1
TexRex2002
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Default Boring the 257

Given the difference in opinion over the strength of the 257's stock sleeves, what are some of your thoughts on boring it oversize to accept forged pistons?

I'm thinking the 100mm pistons, so I guess that would be a .020" overbore or so...

Is the cylinder liner already to thin, or is a mild overbore ok?

Anyone have experience with a bored block?
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Old 07-20-2005, 02:04 AM   #2
Javier
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I'm not really sure of this answer, but I've heard that the sleeves aren't as thing as originally thought... However, I have heard of some ovaling to them. I'm in the middle of doing a 2.5L buildup and opted to use crawfords long pauter rods to reduce the stress on the cylinder walls...
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Old 07-20-2005, 02:10 AM   #3
02Toyowrx
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100mm is the limit. another option would be to go to darton dry sleeves, so you would just about retain the same OEM cooling properties and have the strength.
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Old 07-20-2005, 01:22 PM   #4
TexRex2002
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hmmm... I wonder if I could just hone the walls out and then order custom pistons from Axis or Crawford. Maybe that would be a better option? I wonder if the pistons would be more expensive...
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Old 04-02-2006, 03:08 AM   #5
Boostup!
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Quote:
Originally Posted by TexRex2002
Given the difference in opinion over the strength of the 257's stock sleeves, what are some of your thoughts on boring it oversize to accept forged pistons?
Does the STi EJ257 actually have sleeves in them? Are they iron sleeves? I thought it was all aluminum with some kind of coating. Can someone confirm this? I am wanting to replace my pistons with 100mm ones but I am not sure what the cylinder wall material is. I was told you cannot overbore the coated walls (all aluminum bore) as simply as you can cast iron sleeves.
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Old 04-02-2006, 10:00 AM   #6
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I am pretty sure they are iron sleeves in the ej257
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Old 04-02-2006, 10:11 AM   #7
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ha...
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Old 04-02-2006, 11:12 AM   #8
Starkiller
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I've confirmed iron sleeves in bores. Aluminum doesn't rust.
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Old 04-02-2006, 11:39 AM   #9
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100mm is the max that you can bore the stock block with even a close idea of being able to handle power. You can get 100mm sleeves from darton that are very strong. They say you can bore those out to 102mm but if your motor goes boom so does your sleeves and everything. And at 102 it will still be much weaker.
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Old 04-02-2006, 12:45 PM   #10
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Aluminum doesn't rust is a good observation. I feel stupid now because I DO remember seeing some light rust in my bores after they were washed and I even put some WD-40 in there to stop any further rust.

So the Darton sleeves require the stock sleeves to be completely machined out, I assume? Any precautions needed to prevent the new sleeves from settling more after engine start up and losing compression load on the head gasket? I remember that being a problem for some people here.
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Old 04-02-2006, 01:16 PM   #11
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Steel liners on all Suby blocks that I know of. The 2004 manual states that 0.020 overbore is the limit. I overbored to fit Mahle 100 mm pistons, can't say what the effect is long term, but short term it's fine.
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Old 04-02-2006, 01:44 PM   #12
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Well, I'll let you know how my 100.5mm pistons work out then...
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Old 04-03-2006, 10:49 PM   #13
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Quote:
Originally Posted by Javier
Well, I'll let you know how my 100.5mm pistons work out then...
^^ +2

100.5mm here as well. For you guys making guesses on the max bore size, just take a look in the iron liner where the wrist pin hole is and you can clearly see the thickness (or lack there of). After inspecting the block liners, my machinist said it had enough wall thickness so that's what we went with. Although, he mentioned the iron liners weren't perfectly uniform in the cast outter sleeve portion so each block may be a different case. 100.5 is the absolute max though!
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Old 04-03-2006, 11:00 PM   #14
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Well, that's good to know. Maybe this block will see even more miles if I can bore to 100.5. Where are you getting those pistons?
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Old 04-03-2006, 11:11 PM   #15
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Custom through Wiseco. Next step for me is sleeved though, which I don't plan on doing for a LONG time (knock on wood).
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Old 04-04-2006, 12:03 AM   #16
Javier
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^^ Same. I don't plan on needing to sleeve this thing, but it's the next and only viable option if something should ever happen to the motor as it sits...
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Old 04-04-2006, 02:31 PM   #17
TypeC
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The thing to ask is, have you ever seen someone crack a 257 sleeve?
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Old 04-04-2006, 03:59 PM   #18
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Quote:
Originally Posted by TypeC
The thing to ask is, have you ever seen someone crack a 257 sleeve?
I have not but anything is possible I guess. Aside from the iron liner, the aluminum casting that encases it is pretty hefty looking. I think it would take some extreme pressure to split it. And as far as ovalling, it has the aditional semi closed support at the top.
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