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#1 |
Scooby Guru
Member#: 456
Join Date: Oct 1999
Chapter/Region:
NWIC
Location: Redmond, WA, USA
Vehicle:2008 Forester XT Steel Gray Metallic |
![]() The intent of this thread is to collate information about the STi pistons.
If you want to whine and complain about wanting to start a class action suit because you were sure the car had forged pistons and you wanted to run it at 500HP then please go to SOA Issues forum. I will leave this thread open and sticky under the rules that it strictly stay on the topic of the technical information about the pistons, and published descriptions.
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#2 | |||||
Scooby Guru
Member#: 456
Join Date: Oct 1999
Chapter/Region:
NWIC
Location: Redmond, WA, USA
Vehicle:2008 Forester XT Steel Gray Metallic |
![]() Subaru Australia Forester XT description: http://subaru.com.au/downloads/929305.pdf
Quote:
Subaru Media info for STi: http://vocuspr.vocus.com/VocusPR30/D...0-65d2b0f27407 In the section "300 Horsepower and ..." it says the STi has forged aluminum alloy pistons. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ SOA STi News Release on subaru.com: http://www.subaru.com/content/newscm...ry=2&article=8 Quote:
Car and Driver Forester XT review: http://www.caranddriver.com/article....rticle_id=6854 Quote:
Most of these from Jon in CT. ![]() ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ From Specul8r: Quote:
Info posted by APS Australia: http://forums.nasioc.com/forums/show...hreadid=456606 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Other random stuff: From subaru.com STi specs: http://www.subaru.com/shop/specifica...I_SEDAN#engine (it is silent on pistons) Quote:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Part numbers for USDM STi: 12006AC390 (std grade A) 12006AC400 (std grade B) 12006AC410 (OS 0.25mm) 12006AC420 (OS 0.5mm) Last edited by ANZAC_1915; 12-07-2003 at 11:51 AM. |
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#3 |
Scooby Newbie
Member#: 45702
Join Date: Oct 2003
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![]() Since RalliSpec was the original source of information that led to the mayhem in the original thread (which I just now read for the first time since I rarely have the opportunity to visti NASIOC), I felt compelled to say a few things.
First off, the information posted on the website regarding the Ver.8 piston (which was uploaded around a year or so) was based on the marketing brochure for the 2002 STi model in Japan. In this brochure they clearly described a change from the forged pistons used previously to a new type of cast piston which they claimed resulted in a 20% improvement in strength. This applied to all Japanese STi models. They did not specify what this new casting method was. In reviewing various technical resources on piston technology I took an educated guess and said that perhaps it was a hypereutectic design. But I have no information from Subaru one way or another on this. Hypereutectic pistons are cast with increased silicon content. Basically so much silicon is added to the aluminum that not all of it will be absorbed by the aluminum and therefore silicon particles are suspended in the aluminum forming a matrix. This improves the temperature limit of the piston, helps control the expansion characteristics of the piston, and has other benefits. To be honest I do not know all of the details. There are some downsides to hypereutectic pistons as well. Forged pistons also have their strengths and weaknesses. Forged pistons have a high temperature limit and improved toughness over cast pistons....and therefore will withstand detonation better. Forged pistons, however, expand at a higher rate then cast pistons. This requires increased piston to wall clearances in order that the pistons do not seize in the bore once up to operating temperature. Therefore forged pistons are noisier when not up to operating temperature and this can also lead to increased waar rates on road cars where the engine spends a good deal of time under idle and light cruise conditions. Some types of forged pistons are worse in this regard then others as it has a lot to do with the alloy used. I believe STi will have used a forged piston with a lower expansion rate. I do not have any information on the EJ257 piston outside of what is publicly available. I can say with some certainty, however, that these pistons are not forged. It is easy to tell a cast piston from a forged one by looking at the backside of the piston. Forged pistons have a smooth appearance to the grain of the metal and usually you will see a wide parting line somewhere (usually one the pin bosses if it has not been ground away). Cast pistons have a rougher finish (where they have not been machined) and usually there will be evidence of casting flash. As for cost....forged pistons are almost always more expensive simply because forging is a more expensive process. The forging dies are very expensive to manufacture and they require some serious equipment to provide the thousands of tons of pressure typically used. However, economy of scale also comes into play. Only STi models had forged pistons and previous to the release in Europe, North America, and elsewhere these models were produced in small quantities. Therefore the cost of buying replacement pistons from Subaru is quite high. The price of one single STi 2.0L piston is 23,000yen retail cost in Japan. With the release of the new cast 2.0L piston for the STi, this price still has not changed. Perhaps it will in the future as more and more STi models are produced. As for the EJ257 & EJ255 (which are identical in almost every way except turbo & intercooler), I do not know why SOA chose to price the pistons (or shortblocks for that matter) at such low cost. I can easily find a thousand part numbers that are rediculously expensive from SOA when compared to buying from Japan...and then I can find a thousand part numbers where the opposite is true. As for STi 2.0L engines being hand built and 2.5L engines being mass produced. This is a fallacy....they are both essentially mass produced. I don't think you will find some old Japanese dude hunched over a cylinder head somewhere porting away to his heart's content. Some special models like the 22B, S201, S202 and perhaps even the Spec C's probably recieve a little bit of extra attention. But all in all, these motors are built with the same precision as the ones we are getting. This is production line manufacturing. Well I hope I cleared up a little bit of confusion. Dave RalliSpec, Ltd. www.rallispec.com |
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#4 |
Scooby Newbie
Member#: 45702
Join Date: Oct 2003
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![]() Oops...sorry, the information came from the 2003 model STi brochure (Ver.8....aka revision "C").
--Dave RalliSpec |
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#5 |
Scooby Specialist
Member#: 13095
Join Date: Dec 2001
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![]() Thanks Dave.
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#6 |
Scooby Newbie
Member#: 50098
Join Date: Dec 2003
Location: Nipomo CA
Vehicle:1993 Mazda RX7 Red R1 |
![]() (edited by GW - info already contained in links on 1st post)
Last edited by ANZAC_1915; 12-11-2003 at 03:08 PM. |
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#7 |
Scooby Specialist
Member#: 37101
Join Date: May 2003
Chapter/Region:
MWSOC
Location: B-N
Vehicle:2008 WRX |
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Last edited by ANZAC_1915; 12-11-2003 at 03:09 PM. |
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#8 | |
*** Banned ***
Member#: 2992
Join Date: Nov 2000
Chapter/Region:
NESIC
Location: Connecticut, USA
Vehicle:02 WRX Sedan Silver |
![]() Does SOA's 2004 New Model Update technical reference booklet shed any light on this issue? The description for that document says:
Quote:
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#9 | |
Scooby Guru
Member#: 456
Join Date: Oct 1999
Chapter/Region:
NWIC
Location: Redmond, WA, USA
Vehicle:2008 Forester XT Steel Gray Metallic |
![]() Quote:
A good book to get, glad SOA is finally selling them direct. Pity the poor people who paid big bucks on ebay to get one... Glenn |
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#10 | |
![]() Moderator Member#: 922
Join Date: Feb 2000
Chapter/Region:
MWSOC
Location: Schaumburg, IL
Vehicle:16 WRX (white) 04 FXT (red) |
![]() From this post:
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#11 |
Scooby Newbie
Member#: 49540
Join Date: Nov 2003
Location: Eugene, OR
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![]() I'll just say that cast does not mean crap. My last car came with a 1.6L turbo motor using cast pistons that routinely handled 400 HP without problems. If we can expect anywhere near that kind of realiability, these motors should be able to put out over 600 HP with proper tuning.
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#12 | |
Scooby Newbie
Member#: 50398
Join Date: Dec 2003
Location: Cincinnati-Dayton
Vehicle:2003 WRX Wagon Silver |
![]() Quote:
I'm not sure how they work in a non-nitrous engine. |
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#13 |
Scooby Newbie
Member#: 49936
Join Date: Dec 2003
Location: Spokane WA
Vehicle:2004 STi WRB |
![]() Spoke with SOA this morning regarding the cast/forged debate. I asked the rep on the phone for clarification. After being on hold for about ten minutes while she checked, she responded that they were indeed forged aluminum. I told her that a well-known performance company disputes their claim. She stood by her statement, and said that she'd talked to a Subaru technician at her location, and had found it in an STi reference guide that she had access to. Either the pistons are forged, or every Subaru rep that I've been in contact with via phone and email has lied.
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#14 |
![]() Moderator Member#: 922
Join Date: Feb 2000
Chapter/Region:
MWSOC
Location: Schaumburg, IL
Vehicle:16 WRX (white) 04 FXT (red) |
![]() Not lied, been misinformed. They just have access to the same marketing documents that we've all been fed since the beginning of time.
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#15 |
Scooby Specialist
Member#: 6162
Join Date: Apr 2001
Chapter/Region:
South East
Location: Orlando, FL. USA
Vehicle:2002 WRX MBP, 1st WRX Ever in FL. |
![]() Just to add more fire to this debate, SOA said they have been asked this question so many times that it has now gone back to SOJ for discussion. The conclusive response was that the STI pistons were INDEED forged. This is as of today.
We are going to have to do something about this. They are not selling what they are...selling. The sad thing is, they don't even know. Is there actually any desire to do something about this? Or should we just be refered to the implied whineyness of the SOA issues forum. |
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#16 |
![]() Moderator Member#: 922
Join Date: Feb 2000
Chapter/Region:
MWSOC
Location: Schaumburg, IL
Vehicle:16 WRX (white) 04 FXT (red) |
![]() Do something about what? What do you care about the construction techniques, as long as it can put up to a stock 100k miles, it is perfectly fine for them to be selling.
And perhaps adding some actual information to your post up there to bump it out of the 'rumors' catagory would be a decent idea. |
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#17 |
Scooby Specialist
Member#: 14364
Join Date: Jan 2002
Chapter/Region:
MWSOC
Location: Saint Louis, MO
Vehicle:2003 WRX, '06 Armada 05 Vette & 05 STi (sold) |
![]() Yeah for sure, anyone can look at any new age STi piston and tell its cast. Version 8 JDM STi and USDM 2.5 STi both have similar casting marks. Version 7 were obviously forged.
Im sure they switched for a certain reason. US STi piston: ![]() Pictures: 1st pic is Ver 7 STi piston from APS website ![]() 2nd Picture is Ver 8 STi vs. ROSS forged piston. 3rd picture is of the underside of both... NOTE the similarities to the USDM STi piston with the JDM 2.0 ver 8 STi piston. 4th picture is of JDM ver 7 STi piston from APS. ![]() |
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#18 | |
Scooby Specialist
Member#: 6162
Join Date: Apr 2001
Chapter/Region:
South East
Location: Orlando, FL. USA
Vehicle:2002 WRX MBP, 1st WRX Ever in FL. |
![]() Quote:
How about do something about the fact that they are not selling what they claim to be selling? If I purchase a vehicle that is advertised to have 18" wheels, and it comes with 17"s, I'm not just going to say "oh well, it's ok, they think it's just as good". If they are not forged, then they should not be advertising, telling people and "verifying" that they are forged when they obviously are not. How much clearer can this be? I am frankly surprised to see someone as experienced as yourself taking this position. I apologize, I should have clarified that I called for myself to find out the answer. That is simply what I was told when they called me back with the answer. I called on 2/23/04 at about 2:00pm. I didn't record it, if that's what you are wanting. I can do so next time, if you like. |
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#19 |
![]() Moderator Member#: 922
Join Date: Feb 2000
Chapter/Region:
MWSOC
Location: Schaumburg, IL
Vehicle:16 WRX (white) 04 FXT (red) |
![]() I'm not arguing a point like 17 or 18" wheels, I am arguing a point like if the block was high pressure cast or just low pressure cast. It does not matter to any normal driver and it is not in their paperwork for the vehicle. Everything anyone has ever quoted was stated that it was "based on" a forged internal motor, not that it was one.
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#20 |
Scooby Specialist
Member#: 6162
Join Date: Apr 2001
Chapter/Region:
South East
Location: Orlando, FL. USA
Vehicle:2002 WRX MBP, 1st WRX Ever in FL. |
![]() You are correct, in fact. I just noticed that the original information regarding their being forged on the main website has changed.
I am still volunteering to have these analysed to put this to an end. Anyone care to donate a broken (or whole) ej257 piston? I have already contacted a consulting materials engineer in the area who is willing to provide an affadavit regarding their construction process for a relatively modest fee. www.materialsengineer.com |
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#21 |
Scooby Newbie
Member#: 49936
Join Date: Dec 2003
Location: Spokane WA
Vehicle:2004 STi WRB |
![]() I'm with you Conduit. When I purchased my car, the Subaru website stated that the pistons were forged. That said, I don't mind necessarily if they're not forged, as long as there is a good reason that they went to cast. All I'm really looking for is some factual information from Subaru about their decision to abandon their forged pistons. I'd like to see some specs, and technical data on the pistons that reside in my engine. Tell me they're not the same type of design that is in an engine that was designed with 165 horsepower in mind. Tell me that they're constructed in a way that leads me to believe that they'll live up to the reputation for quality, and durability that previous STis are known for. I'll tell you this: If I ever have any piston related problems, with my stock motor, I'll be visting my attorney--I don't care if the warranty is up, or not.
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#22 |
Scooby Newbie
Member#: 51138
Join Date: Dec 2003
Chapter/Region:
NESIC
Location: CT
Vehicle:2015 LE STI WRB |
![]() I think we're all in agreement now that these ARE in fact cast, but to put the last nail in this issue I asked an STi design engineer about this (automotive industry contact in Japan) and he also confirmed they are a new high strength cast alloy. To go much further, we are treading on Subaru's core technical secrets - do we really think they OWE it to us to offer all technical details which the Mistubishi engineers would just love to get their hands on?? Sure it'd be nice, but don't hold your breath for their forged vs. new cast dyno fatigue life data...Bottom line, as we upgrade just avoid detonation and we should be ok for fatigue life. Like specul8r said, if a stock setup blows a piston, there's a problem...
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#23 |
![]() Moderator Member#: 922
Join Date: Feb 2000
Chapter/Region:
MWSOC
Location: Schaumburg, IL
Vehicle:16 WRX (white) 04 FXT (red) |
![]() Axis Power Racing has already taken one of the pistons to be analized at CP. See my post halfway up the page.
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#24 | |
Scooby Specialist
Member#: 14364
Join Date: Jan 2002
Chapter/Region:
MWSOC
Location: Saint Louis, MO
Vehicle:2003 WRX, '06 Armada 05 Vette & 05 STi (sold) |
![]() Quote:
-Mike ![]() |
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#25 |
Scooby Guru
Member#: 456
Join Date: Oct 1999
Chapter/Region:
NWIC
Location: Redmond, WA, USA
Vehicle:2008 Forester XT Steel Gray Metallic |
![]() The pistons are cast - no need to do an analysis.
Any pointers to current advertising material that says they are forged? If not, back to our usual programming. |
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