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Old 12-03-2007, 10:06 PM   #1
1GR8WRX
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Member#: 18792
Join Date: May 2002
Chapter/Region: MWSOC
Location: Chicago
Question Need Piston Advice for Hybrid

I have too much conflicting information right now from NASIOC and from various other Subaru sites in regards to piston selection. I read Una's FAQ at least 5 times over the past 13 months that I've been staring at my dead '02 WRX, but I'm still looking for a level of "confidence" in regards to using the stock STi pistons for my hybrid 205/257 build.

My power goal was (still is?) 350whp. Here are my relevant supporting mods:
  • OEM STi EJ257 shortblock
  • OEM EJ205 heads
  • Supertech valves (stock diameter)
  • Brian Crower valve springs & retainers
  • Crower 264/264 cams
  • OEM STi headgaskets
  • Perrin Fuel Rails
  • Helix 660cc injectors
  • Walbro 255lph fuel pump
  • Forced Performance Evo III 16g ported turbo
  • Perrin turbo inlet hose
  • STi timing belt
  • ACT Streetlite Flywheel
  • Spearco top mount intercooler
  • Silicone turbo to intercooler hose
  • Custom intercooler water mist system
  • Gruppe-S catless uppipe
  • Stromung catless short 3" downpipe (ceramic coated) w/divorced wastegate
  • Thermal R&D catback
  • EGT sensor (tapped in #4 exhaust)
  • LC-1 wideband O2 sensor (installed in downpipe right after turbo)
  • GM Boost solenoid
  • UTEC
  • OpenECU (Tactrix cable)

So the two questions that I have are:

1. Is my power goal of 350whp attainable (I thought it was as I was going forward with all of those purchases...)? I figure that's around 450hp at the crank.

2. Will I need forged pistons to avoid having to break open this engine again anytime soon? I am a bit fearful of the hypereutectic pistons.

For those who are interested, I think it's basically ready for the power:
  • ACT Street Clutch
  • PPG 1-4 gears

Thanks for any advice!

-1GR8WRX
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Old 12-03-2007, 11:25 PM   #2
Eskram
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Chapter/Region: South East
Vehicle:
2004 2.5 Hybrid 18g
Wagon + LGT 1-4 g00dness!

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To avoid later headaches, put a set of forged slugs in it - Do it right, once.

Eskram - who wishes he heeded his own advice.
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Old 12-04-2007, 12:02 AM   #3
bad mutha
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Location: Hotashell,Fl
Vehicle:
04 forester xt
crp

Cool

cp pistons are really good, so are a bunch of other ones...
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Old 12-04-2007, 12:17 PM   #4
TypeC
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02 2.5LWRX-Retired
335i w/twins

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I would skip the following parts:

Quote:
Originally Posted by 1GR8WRX View Post
  • Supertech valves (stock diameter)
  • Perrin Fuel Rails
  • Forced Performance Evo III 16g ported turbo
  • STi timing belt
  • ACT Streetlite Flywheel
You don't need any of that, and I'd get a different, proven turbo that isn't screaming just to get those numbers. I'd suggest a FP green/SZ49. 350whp easily, more on race gas. You'll want the room to grow. You also might go FMIC at this point. It was better in every way (temp consistency, power, etc) on my Hybrid.

$.02
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Old 12-04-2007, 01:10 PM   #5
AWDWRXLOVER
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Vehicle:
02 built hybrid
sr55/meth/sick speed

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does anyone know what pistons are available for hybrids? as in lower compresion than stock sti so we dont have to use cometic or rs hg.
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Old 12-04-2007, 03:36 PM   #6
kwlsti
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Location: Toronto, Canada
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2004 STI
BLACK

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i'd go with CP pistons too

have fun
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Old 12-04-2007, 06:52 PM   #7
Devan M
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Crawford stocks custom forged pistons with offset wristpins for the STI shortblock / WRX head hybrid that lower the compression ratio to a useable 8.2 to 1

Ask for S2 WRX pistons

Last edited by Devan M; 12-05-2007 at 01:38 PM.
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Old 12-04-2007, 11:04 PM   #8
brcewane
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Location: Ontario
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2002 WRX
Flat Grey

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Quote:
Originally Posted by TypeC View Post
I would skip the following parts:



You don't need any of that, and I'd get a different, proven turbo that isn't screaming just to get those numbers. I'd suggest a FP green/SZ49. 350whp easily, more on race gas. You'll want the room to grow. You also might go FMIC at this point. It was better in every way (temp consistency, power, etc) on my Hybrid.

$.02
Ditto on this one.. go with FPGreen or at least a 20G to get the numbers you are looking for.. 16G isn't going to get you there without pushing that biotch to the point of no return. You will also likely want 740 cc injectors to fuel that kind of HP as well.
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Old 12-05-2007, 11:33 AM   #9
R & H Garage
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Default

EVOIII 16G is only rated for 395hp anyway. If you raise the compression ratio over 8.5:1 you can get more out of it. Regardless, the turbo is working hard and you probably won't get to the 350whp mark. Plus without an external wastegate the pressures in the exhaust from the small turbine will be way too high and will limit your power.

Your current combo isn't too hot, as you know, or you wouldn't have made the thread.
COBB will make you custom pistons. They have a piston order sheet that has all the parameters you want. They use very nice JE forgings.

Crawford has them as well, but they use CP forgings. The CPs don't have an offset wrist pin and are a bit noisier. If piston slap isn't something you are worried about, then the CPs are nice. They are rumored to have the truest ( most square) ring lands out there.

Wiseco will make you custom pistons as well, if you want to wait.

What year EJ257 block are you using? If it is 2007, then the pistons are already set up for a 46cc combustion chamber and will match the WRX heads nicely with an 8.2:1 compression ratio. All previous years are set for the 51cc chambers and will yield a much higher and undesirable compression ratio.

I would also not use Helix injectors or PE injectors on the factory ecu. They are a nightmare to tune.

For 1,500 bucks, Ron at Axis Power Racing will port your heads to help compliment your setup. That's a steal of a deal and anything that helps to increase flow out of that engine should be done.

Hope that helps a little.

-Dominic
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Old 12-05-2007, 01:45 PM   #10
TypeC
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335i w/twins

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Quote:
Originally Posted by KitoAutoSport View Post
All previous years are set for the 51cc chambers and will yield a much higher and undesirable compression ratio.
There are many other threads calculating true CR with the 257 shorty. Mid 8's:1 isn't highly undesirable IMO.
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Old 12-05-2007, 11:09 PM   #11
1GR8WRX
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Smile Thanks for all the input!

I wanted to thank everyone for the input so far. I know I don't have the ideal setup, but that's mostly because I've been tacking on mods one by one since I purchased the car in March 2001. I'm pretty sure that I'm not alone in having a power goal that seems to increase over time

TypeC, I already have everything on the list. The car has 80k on it, so I thought the timing belt made sense. The turbo only has maybe 2k on it - I didn't expect my transmission and then a piston ring to go within 2 months of installing the turbo. It probably wasn't the turbo that did it, but the 4 launches every day driving to and from work on my own (probably poor) UTEC street tune...

Since I have the heads off, I figured a pressure test and a valve job at 80k seemed to make sense as well. Especially since I was doing cams and higher-rate springs. Basically, I'm trying to make sure that I don't have to pull the engine again. If I have to upgrade the turbo, injectors, etc. at a later date to reach my power goals, at least it's more bolt-on. The Perrin fuel rails are hopefully an insurance policy - I know there are multiple theories out there about why cylinder 4 gets killed, but I don't want the fuel system to be a potential culprit.

KitoAutoSport, I just bought the block from Royal Performance (Fred Beans Subaru), so I'm guessing it was made in 2007. It's still sealed in the box on a skid in my garage. That is good info to know about the combustion chambers being different depending on the year...probably should have known that with all the lurking I do on this site. Can you elaborate on why the Helix injectors are tough to tune on the factory ECU?

What I'm hearing so far is that my supporting mods are limiting me (not totally suprising), a few people recommended certain piston brands over others, and Eskram said definitely do the pistons. I might take those suggestions on piston brands as an endorsement for upgrading. It sounds like I probably can't go wrong with CP or Cobb, given my goals.

Thanks again, everyone! And yell at me later if I ever drive this thing without a pro-tune.

-1GR8WRX
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