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Old 10-23-2007, 12:11 AM   #1
morrocco88
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Default EJ257 BUILD ADVISE - Piston Question

I need some advice on my build.

EJ257 short block - MY98 Legacy 2.5 NA DOHC Heads (46cc Combustion Chamber) Using stock sti headgaskets.

I've been searching and reading every thread I could about forged pistons. I bought a used short block with about 24K miles on it with low compression on #4. The bore looks perfect and just like the other three.

My plan is to buy custom forged pistons to handle the little bit of extra power and to get the compression ratio down to about 8.2:1. My power goal is not that crazy, 300 ft. lbs. of torque to the wheels would be nice. I want the motor to be as quiet as possible and to live as long as possible since it is mainly a street car.

I'm just confused as to what pistons to get. From my searching I've concluded I would probably want the 4032 forged, as tight of piston to sidewall clearance I can get away with, and offset pin location like the stock piston design.

What company would fit the bill here? Can you get the 4032 forgings with custom specs? Would I just ask for the stock spec pistons and just have more dish to lower the compression?

Any thoughts or advice would be nice. Thanks!
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Old 10-23-2007, 12:20 AM   #2
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I've got a set of NIB Arias forged pistons in 4032 alloy, 8.3:1 CR that are 99.5mm (standard bore) if you're interested. PM me if interested.

Jay Storm
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Old 10-23-2007, 12:26 AM   #3
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Just be sure to get them coated, whatever brand you choose.
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Old 10-23-2007, 12:32 AM   #4
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JE's off the shelf pistons for the phase 1 ej25 are 8.2:1 of course pending your deck height, like all pistons.
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Old 10-23-2007, 12:33 AM   #5
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^^ Are you talking about skirt coating, or crown coating or what?
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Old 10-23-2007, 12:47 AM   #6
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Quote:
Originally Posted by morrocco88 View Post
^^ Are you talking about skirt coating, or crown coating or what?
Coated skirts will help reduce noise like you want.
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Old 10-23-2007, 12:52 AM   #7
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Quote:
Originally Posted by Homemade WRX View Post
JE's off the shelf pistons for the phase 1 ej25 are 8.2:1 of course pending your deck height, like all pistons.
Are the JE's the 4032 alloy? And is the EJ25 deck height the same as the EJ257?
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Old 10-23-2007, 01:07 AM   #8
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I am using the Mahle PowerPak piston set currently. They are silent at start up.
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Old 10-23-2007, 01:18 AM   #9
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Quote:
Originally Posted by morrocco88 View Post
Are the JE's the 4032 alloy? And is the EJ25 deck height the same as the EJ257?
yes, but what I was getting at is if you deck your block or run a different thickness head gasket...

as for the alloy, I'm not sure...where's Nick when you need him
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Old 10-23-2007, 01:49 AM   #10
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I am using the Mahle PowerPak piston set currently. They are silent at start up.
Are these "off the shelf", or were these custom made? I know you have an sti crank and rods in the NA 2.5 block right?
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Old 10-23-2007, 01:56 AM   #11
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Quote:
Originally Posted by morrocco88 View Post
Are the JE's the 4032 alloy? And is the EJ25 deck height the same as the EJ257?
Mine are the 2618's. I know that JE makes both; I don't know if they do 4032's on a "shelf" basis, but I'd think they would for a custom order. Call 'em, they're not that much more.
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Old 10-23-2007, 02:18 AM   #12
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Thanks - I think I will have to start calling some manufacturers. I was just trying to get some feedback from people here that have maybe built some motors like mine. I've already figured these would have to be custom to get my lower CR with the 46cc heads. So far I've got a quote from crawford (cp pistons) via email and it was like $670, and Techworks shows a price of like $750 on their web site, but haven't replied to my email yet.

I like the idea of the crawford pistons because he has built this motor before and has a piston designed for it, but I don't think they have an offset pin, and are the 2618 alloy and have a .0035 recommended clearance.
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Old 10-23-2007, 04:03 AM   #13
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Quote:
Originally Posted by morrocco88 View Post
Are these "off the shelf", or were these custom made? I know you have an sti crank and rods in the NA 2.5 block right?
100mm off the shelf EBAY purchase. Took a piston and the block down to my machine shop and they charged me $40 to bore the block.
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Old 10-23-2007, 05:07 PM   #14
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Quote:
Originally Posted by morrocco88 View Post
Thanks - I think I will have to start calling some manufacturers. I was just trying to get some feedback from people here that have maybe built some motors like mine. I've already figured these would have to be custom to get my lower CR with the 46cc heads. So far I've got a quote from crawford (cp pistons) via email and it was like $670, and Techworks shows a price of like $750 on their web site, but haven't replied to my email yet.

I like the idea of the crawford pistons because he has built this motor before and has a piston designed for it, but I don't think they have an offset pin, and are the 2618 alloy and have a .0035 recommended clearance.
I think Crawford has been using offset wrist pins for over two years now

You might want to call them to confirm though.
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Old 10-24-2007, 11:22 AM   #15
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cp pistons are 4032
but are not coated.
you could just replace with stock sti pistons
to achieve your power goals and call it a day.
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Old 10-24-2007, 12:11 PM   #16
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What would that make the compression ratio? The stock sti heads have 50 or 57cc? I've found conflicting info on different threads here. My heads have 46cc. So your saying just use the stock design pistons and then tune for the higher compression?

I'm looking into some Cobb pistons that are designed for the heads i'm using, and they are pretty reasonable in price. I can also specify which CR I want since they are custom made to order. Cobb's are JE's made to their specifications I believe. Anybody running them?
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Old 10-24-2007, 01:11 PM   #17
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Me. So far, they go up and down like they should.
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Old 10-24-2007, 05:17 PM   #18
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CP's are suppose to be drop ins.
the cr is also suppose to be stock.
you could also use a thicker head gasket..
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Old 10-24-2007, 06:48 PM   #19
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compression is stock if your running stock sti heads, and I don't want to use a thicker head gasket because I want to keep a good quench or squish.

I thought cp's were the 2618 alloy. I think I have it narrowed down to either Cobb or Crawford, but I'm waiting for an email back from Cobb. I think using a custom piston designed for use with the combustion chamber on my heads will be best.
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Old 10-24-2007, 08:07 PM   #20
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Quote:
Originally Posted by morrocco88 View Post
I thought cp's were the 2618 alloy...
I thought so too, maybe he mistook one for the other? Up until not so long ago, Mahle was the only option in the 4032 alloy.
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Old 10-24-2007, 11:39 PM   #21
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[quote=morrocco88;19805412]The stock sti heads have 50 or 57cc? I've found conflicting info on different threads here. My heads have 46cc.QUOTE]

Has anybody cc'ed the stock sti heads and knows for sure?
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Old 10-25-2007, 02:10 AM   #22
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Old 10-25-2007, 02:17 AM   #23
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Why don't you want to run a 2618 piston?? They are a bit noiser as they expand more but it is a stronger alloy. I thought mahle was the only off the shelf 4032 option. The new mahle is a different alloy from 2618 and 4032. It is called MSP25. Mahle says they are holding 30+psi without issue so so far.
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Old 10-25-2007, 01:09 PM   #24
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^^^ Because for the power levels I'm going to be at, I don't need the stronger alloy, and this is a DD, so I'm trying to make it as quiet as I can.

Maybe I should just use the 2618 and run tighter than recommended clearances. Plus I know that the Cobb pistons are 2618 and I'm pretty sure the crawford's are too. I'm going to call today to find out for sure. I'm also going to ask if they have the offset pin design.
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Old 10-25-2007, 01:54 PM   #25
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You don't even need to do that really. We have done several sti shortblocks with just a set of je's. They are a bit noisy on start up but quiet down considerably. I have just seen a few 4032 failures it doesn't make sense to run them.
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