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Old 10-20-2010, 11:21 PM   #1
AlaskanProtege
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Default 2.3 hybrid build

ok, i have a 02' ej2.5 sohc 90k miles..... and a 05' ej2.0 out of a wrx w/ 30k miles....... i wanna take the crank and bearings from the 2.0 and put them in the 2.5 block and use the 2.5 rods and pistons and stock 2.5 heads..... and run about 6-8 psi of boost. am i missing anything? i know its not the sti block or internals but it should be a large step up from this 1.8NA.....also when i split the case are the bolts reuseable? or torgue to yeld? also i plan on running head studs aswell hopefully prevent head gasket failure under load... besides new rod bearings piston rings and gaskets i should be set right? any in sight would be awesome!!
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Old 10-21-2010, 11:02 AM   #2
Homemade WRX
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um, if you are just running stock rods and pistons, you're CR will be dropped so much you can run a fairly healthy amount of boost...

I'd opt for EJ257 off the shelf piston; that matched with the 131.6mm rod from the NA EJ25 will put your quench height (excluding headgasket) around .9mm lower than stock. Either way, compression is going to be low, so run the numbers really quickly for both options. JE does have a slightly higher CR model piston available off the shelf too.
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Old 10-21-2010, 05:01 PM   #3
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Originally Posted by Homemade WRX View Post
um, if you are just running stock rods and pistons, you're CR will be dropped so much you can run a fairly healthy amount of boost...

I'd opt for EJ257 off the shelf piston; that matched with the 131.6mm rod from the NA EJ25 will put your quench height (excluding headgasket) around .9mm lower than stock. Either way, compression is going to be low, so run the numbers really quickly for both options. JE does have a slightly higher CR model piston available off the shelf too.
hmmmmmmm... i need to find a way to build this de-stoker w/o dropping CR below 9.0:1..... i guess i dont really need to destroke it but i love the uniqueness... if i run a stock gasket with no major machineing to the heads any ideas how to figure that CR out? stock is 10:1 right? can i run the 2.0 rods to keep the quench up?
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Old 10-22-2010, 09:18 AM   #4
Homemade WRX
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the NA EJ25 phase 2 rods you have are the longest OEM rods subaru has made. You'll have to crunch some simple numbers to see what your CR will be.

Any reason you can't go below 9.0:1? custom rods or custom pistons can help to correct everything (compression ratio and quench height).

I'd run the numbers but I don't have my massive subaru compression spreadsheet with me...so I don't recall the values of the cc's on your heads or the stock pistons (which IIRC are pretty much flat).
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Old 10-22-2010, 11:42 AM   #5
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Originally Posted by AlaskanProtege View Post
hmmmmmmm... i need to find a way to build this de-stoker w/o dropping CR below 9.0:1..... i guess i dont really need to destroke it but i love the uniqueness... if i run a stock gasket with no major machineing to the heads any ideas how to figure that CR out? stock is 10:1 right? can i run the 2.0 rods to keep the quench up?
I don't know the stats for your particular motor, but as an example an EJ257 block and heads, with std. compression pistons, and a 75mm crank will have a CR around 6.7:1.

You really need a set of +2mm rods and some higher CR pistons (higher than a stock STi set, again, I don't know your motor) if you want to be around 9.0:1.
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Old 10-22-2010, 02:36 PM   #6
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well shooting form the hip, I'll say with the higher cr JE ej257 pistons and his motor, he'll probably be a high 7:1 area...simply because he will have 1.1mm more rod length thus helping to greatly reduce final volume.

a 133.6mm rod would be what you need if wanting to keep your NA EJ257 style piston. 132.5mm if going to an EJ257 piston.
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