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Correct. I was aware of the what the letters meant. For some reason I was under the impression that the WRX case halves used different lettering. It is a single AVCS engine. Could that be what makes it a WRX engine and not a STI engine?
AFAIK, all EJ25 block use that lettering. Not sure about any other EJ-series though. I never bothered to look as I've never owned one. There are quite a few differences between EJ255 (WRX) and EJ257 (STi), S(ingle)-AVCS vs. D(ual)-AVCS are one of them. Internals were slightly different, STi ran slightly lower static compression, and then there's the external differences like turbo and intercooler.

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Correct. I was aware of the what the letters meant. For some reason I was under the impression that the WRX case halves used different lettering. It is a single AVCS engine. Could that be what makes it a WRX engine and not a STI engine?
Correct

the EJ255 and EJ257 are the same case halves. Just lower compression pistons in the STi.

the WRX use Single AVCS heads, B25 IIRC. The STi uses dual AVCS heads, W25 heads.
 

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Discussion Starter #44
Okay. So it is definitely a WRX Block. What distinguishes the lower compression pistons from the higher compression pistons?

Long-term. I will purchase W25 heads. There is also D25 head right?
 

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Discussion Starter #45
With all other engine specs kept OEM, what sorts of adjustments need to be factored for running 99.5mm, 8.5:1 CR piston in stead of 99.5mm, 8.2:1 CR pistons?
 

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Discussion Starter #47
WRX has smaller rods too... Although, they are forged as well.
Yes. I don't plan on reusing the rotating assembly. The Crank, Rods, & Pistons will all be new. Like going with an OEM 79mm CS, forged STI rods, and forged pistons. I'd prefer to go with forged pistons that won't expand as much.
 

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check out 4032 forged pistons then. they are a semi-forged piston. still stronger than hyperuetic but not as strong as 2618 forged.

CP, Manley, JE etc are all 2618 forged.

Arias, Supertech, Mahle and Cosworth are all 4032 forged type pistons.

My next build will be Cosworth,H-tuff and closed deck.
 
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